1
PROFESSIONAL REFERENCE GUIDE updated 21dec07
INDEX
Pg.
contents
1.
Index
2.
How thermostats work
3.
Thermostat general wiring chart
4.
Heat pump operation
5.
2 Wire Heat, Gas millivolt system wiring
6.
2 Wire Heat, 24VAC wiring
7.
3 Wire Heat, and Fan wiring
8.
4 Wire Heat, Fan, and Cool
9.
5 Wire Heat, Fan and Cool (two power wires)
10.
5 Wire 2 heat, fan, and cool
11.
4 Wire Heat Pump
(without auxiliary heat)
12.
5 Wire Heat Pump
(with auxiliary heat)
13.
Zoned Forced Air Heating and Cooling 6 wire (main) 3 wire (remotes)
14.
Zoned hot water systems 3 wire
15.
RV, Swamp coolers, Mobile Home systems
16.
Line Voltage thermostats
(single pole and double pole)
17.
Line voltage cooling and Controlling humidity
18.
Humidifying
19.
De-humidifying using the A/C or using an external de-humidifier
20.
De-humidifying (using an External humidistat)
21.
Thermostat Power (and remote power)
22.
Fan control: Manual, heating, cooling
23.
General Information: swing, anticipator, accuracy, calibrate room temp
24.
General Info continued: Compressor delay, differential, reset
25.
Trouble shooting: fan, heat, compressor, 24VAC, Short cycle
26
Test long cycling, fan not running, random resets, B wire info.
27.
Safety
1
2
THERMOSTATS FOR HVAC (heat, ventilation, air conditioning)
A thermostat is an electronic switch much like a light switch, i.e., the switch is either ON
(contacts closed) or OFF (contacts open). In a thermostat this is done several ways.
1. The old mercury thermostats use a vile of mercury. When the vile is tipped one
way, the mercury closes two contacts at that end by touching them both. When the
vile is tipped the other way, it opens those two contacts. The vile of mercury is
connected to a bi metal spring that reacts to temperature tipping the vile back and
forth. The use of mercury is no longer acceptable, but there are many still in use.
Dispose of mercury very carefully as it is extremely dangerous. Call your local
recycler to find a disposal station.
2. Some mechanical thermostats use a bi metal device that causes the two contacts to
touch or open depending on temperature.
3. Modern electronic thermostats use what is called a magnetic latching relay. This
is a device that has two contacts that close when a coil on the relay is pulsed with
a voltage. To open it, a second coil is pulsed and the contacts open. The voltage
pulses are generated by the electronics inside the thermostat. The electronics is
what makes thermostats different from each other. The purpose of most
thermostats is to close two contacts to turn on an HVAC function and to open
them to turn off that function.
There are 3 main power sources used for switching HVAC functions on and off, Gas
Millivolt (750mv), 24VAC and line voltages of 115VAC or 230VAC.
1. The Gas millivolt system requires the thermostats to switch only about 750Mv
(3/4 volt) to turn on and off the gas heat. Any 24VAC thermostat can be used.
2. The 24VAC systems require the thermostat to switch 24VAC. All low voltage
thermostats will easily switch these two systems on and off. This is the most
popular. These cannot be use for line voltage heating or cooling.
3. The 115VAC or 230VAC is used for electric baseboard, wall heaters, or ceiling
heat; this takes a special “LINE VOLTAGE” Thermostat.
If the old thermostat has 2 or 4 large, stiff wires, coming out of a plastic or metal box in
the wall (J box), it is likely the system is 115/230VAC, and must use a line voltage
thermostat. Connecting line voltage to a 24VAC thermostat is dangerous and will
severely damage the thermostat. Always shut off power before replacing any thermostat.
Standards for identifying low voltage thermostat wiring are set by the National Electrical
Manufacturers Association (NEMA) Standards Publication DC 3-2003. These standards
set down what letters to be used for what function in thermostats. Though many
thermostats adhere to those standards, some thermostats do not. Below is a wiring chart
to help compare wiring letters in most systems. As we discuss various HVAC systems,
we will be using the NEMA standard letters for our thermostats. Refer to this chart when
replacing old thermostats that do not have the same letters as the Ritetemp thermostats.
There is no standard for wire colors.
2
3
VERY IMPORTANT NOTICE!!
BEFORE REMOVING WIRES FROM THE OLD THERMOSTAT, LOOK AT
THE LETTERS NEXT TO EACH WIRE AND MARK THE WIRES WITH THE
SUPPLIED LETTERS. USE THE CHART BELOW TO CROSS REFERENCE.
ANY WIRES THAT WERE NOT CONNECTED TO THE OLD THERMOSTAT
OR NOT USED ON THE NEW THERMOSTAT SHOULD BE TAPED OFF AND
PUSHED BACK INTO THE WALL.
THERE IS NO COLOR CODE FOR THERMOSTAT WIRES
THOUGH THE COLOR OF THE WIRE MAY MATCH THE LETTER OF THE
WIRE, THE COLORS THEMSELVES SHOULD NOT BE CONSIDERED.
OLD THERMOSTAT NEW THERMOSTAT (NEMA standard) DESCRIPTION
WIREING FOR NORMAL HEATING AND COOLING (gas/oil/elect)
(no heat pump)
R, or RH, or 4, or V
RC/RH (connected)
Single power wire
W or H
W
Heat return
W2 or H2
W2
2nd stage of heat
W3
W3
3rd stage of heat
Y or M
Y
Cool return (compressor)
Y2
Y2
2nd stage of cool
Y3
Y3
3rd stage of cool
G or F
G
Fan return
C or X
C
24VAC thermostat power
FOR SEPARATE HEAT AND COOL POWER, REMOVE THE RH/RC JUIMPER
AND WIRE AS SHOWN BELOW:
RH and R
RH to RH and R to RC
RH = Pwr heat and R= Pwr cool
4 and R
4 to RH and R to RC
4
= Pwr heat and R = pwr cool
RH and RC
RH to RH and RC to RC
RH = Pwr heat and RC = Pwr cool
WIRING FOR HEAT PUMP
R
RH/RC (connected) Power
Y
Y and W
Compressor (used for heat and cool)
W2
W2
Heat pump Aux heat
E
W2
Emergency heat
O
O
Changeover (Powered in COOL)
or
or
Do not connect both O and B!
B
B
Changeover (Powered in HEAT)
Florida Heat Pump (4 wire aqua) may use W as changeover (connects to terminal O)
On a heat pump, if O and B are both present, connect O wire to O terminal and B
wire to C terminal (TRANE HEAT PUMP PRODUCTS). Do not connect B wire to
B terminal as it may damage the 24VAC power system.
3
4
ZONED HOT WATER MOTOR VALVES
5 or R
RH
Power wire
4 or W or NO
W
Turn Valve on
6 or Y or NC
A
Turn Valve off
ZONED HOT WATER SOLENOID VALVES
R
RH
power
Y or B or N/O
W
Turn Valve off
W or N/C
A
Turn Valve on
Heat Pump Operation
To better understand heat pumps, go to a drawing at: www.dhclimatecontrol.com/hp.htm
Heat pumps are a unique method of heating. Essentially it is a reversible air conditioner.
An A/C pumps heat out of the house into an outside air exchanger and into the outside
air. A heat pump uses very similar equipment and pumps heat from the outside air into
the inside air exchanger and into the house. The heat pump has a “reversing valve” to go
from COOL to HEAT. An AIR CONDITIONER gets less efficient in cooling a house as
the outside air gets hotter. Similarly, the HEAT PUMP gets less efficient as the outside
air gets colder.
AUXILIARY HEAT (for heat pumps)
In moderate to cold climates, the heat pump cannot keep the house warm if the outside
air gets too cold. Most air exchange heat pumps have an additional heat source called
AUXILIARY heat and is often electric heat strips but can be GAS or OIL. This auxiliary
heat comes on to help bring the house temperature up quicker and/or provide heat when
the heat pump can no longer keep up (outside temp. below 30F). Most heat pump
thermostats have an EMER (emergency) or AUX ONLY switch or button to allow the
auxiliary heat to be the only source of heat if the heat pump quits or can not keep up.
Some heat pumps do not need auxiliary heat if they are used in warm climates and/or if
instead of using air heat exchangers, they can use ground or water (wells) heat
exchanging. Ground and well temperatures stay very constant (typically 60F) so make
excellent heat exchanger medium for pulling out heat (for heating a house), or dumping
in heat (for cooling a house).
Some heat pumps may be 3 stages; 1 stage of compression and 2 stages of aux heat, or 2
stages of compression and 1 stage of aux heat.
4
5
The following drawings will help explain how the thermostats relay control and
operate the HVAC systems.
GAS MILLIVOLT HEAT ONLY 2 WIRE
Below is a typical Gas Millivolt system. When the thermostats relay (switch) connects
RH to W, the heat comes on. If the heating system already has a thermostat connected,
use the same two wires that were on the old thermostat. When there are just two wires,
there is no polarity, i.e., either wire can go to RH or W.
TYPICAL GAS MILLIVOLT HEATING SYSTEM
WHEN RH CONNECTS TO W, THE HEAT COMES ON
RH W
FOR MILLIVOLT GAS HEATERS WITH PILOT LIGHTS
GAS FURNACE, GAS FIREPLACE, SWIMMING POOL HEATER, ETC.
OVERHEAT SWITCH
ON
BURNER
TH TH/TP
MILLIVOLT GENERATOR
PILOT
TP
PILOT LIGHT GAS FLAME
GAS CONTROLLER
OFF
TYPICAL CONTROL
GAS INPUT
5
6
LOW VOLTAGE 24VAC HEAT ONLY 2 WIRE
The drawing below is a typical heating system using 24VAC. The heating system has a
transformer that generates 24VAC to operate the furnace low voltage thermostat
controlled system. The 24VAC is not an electrical hazard. It can use much smaller wire
than line voltage systems, and does not need an electrical box in the wall.
When terminals RH and W are connected together by the thermostats relay
(switch), the 24VAC (RH) connects to the furnace relay (W) and the heat comes on.
When the relay opens the contacts, the heat goes off. This relay is operated by the
thermostats computer which follows your programming commands. Some heating
systems immediately come on. Some take a few seconds. With just two wires, the
heating systems fan is controlled by the furnace, not by the thermostat. With only two
wires, there is no polarity, ie, either wire can go to RH or W.
If a C wire is available at the thermostat, it can be used to run the thermostat in
place of batteries or in addition to batteries for memory back up with longer battery life.
The “C” wire is always available in a 24VAC system as it is the side of the 24VAC heat
transformer that goes to all the HVAC relays. Most HVAC techs can find this point and
run a wire to the thermostat if there is not one. Do not touch RH and C together.
TYPICAL 24VAC, 2 WIRE HEATING ONLY SYSTEMS
IN THE THERMOSTAT, WHEN RH CONNECTS TO W, THE HEAT RELAY CLOSES.
RH W
C
RH
W
P
S
115VAC
24VAC
HEAT CONTROL
RELAY CLOSES FOR HEAT TO BE ON
24VAC TRANSFORMER
HEAT RELAY
FOR ANY TWO WIRE, 24VAC HEATING SYSTEM
GAS, OIL, ELECTRIC, HOT WATER
6
7
24VAC HEAT AND FAN 3 WIRE
The drawing below is a 24VAC, three wire heat control system controlling both HEAT
and FAN. The 24VAC provides power to the HEAT CONTROL relay and the FAN
CONTROL relay through the thermostat.
Most gas or oil heating systems control the fan so the air is not circulated until the air is
heated in the furnace and then left on after the heat is shut off to purge the heat out of the
system; they do not need the thermostat to control the fan.
The G wire allows the thermostat to control the fan when the fan switch is in the ON
position and/or when the GAS/ELEC jumper is in ELEC. Most electric furnaces do not
have a fan control and must have the thermostat turn on the fan whenever the electric
furnace is turned on. This is necessary to circulate the warmed air into the house and
keeps the electric elements from overheating. Some thermostats also leave the fan
running for 1 minute after the heat is shut off to purge the heat out of the system.
TYPICAL 24VAC, 3 WIRE HEATING ONLY SYSTEMS
CONNECTING RC TO G = FAN
CONNECTING RH TO W = HEAT
RC RH
W
G
RC/RH connected
C
RH or R
W
G
115VAC
P
S
24VAC
FAN CONTROL
24VAC TRANSFORMER
HEAT RELAY
FAN RELAY
RELAY CLOSES FOR HEAT
RELAY CLOSES FOR FAN
FOR THREE WIRE, FORCED AIR 24VAC HEATING SYSTEM
GAS, OIL, ELECTRIC
7
8
24VAC HEAT, FAN, AND COOL
4 WIRE
The drawing below is a standard 24VAC, 4 wire heating and cooling control system.
(Not a heat pump). With the thermostats mode switch in the HEAT position, the heating
functions are the same as in the 3 wire heating system.
When the thermostats mode switch is in the COOL position, the thermostat turns on the
air conditioner’s compressor and the air handler circulating fan at the same time.
Note the RC (power cool) and RH (power heat) terminals are connected together. This is
because in a 4 wire heating and cooling system, there is a single 24VAC power
transformer for both the heat and cool.
TYPICAL 24VAC, 4 WIRE HEATING & COOLING SYSTEM
TYPICAL THERMOSTAT
THERMOSTAT POWER
BATTERIES
THERMOSTAT CONTROLLER
THERMOSTAT MICROCONTROLLER
THERMOSTATS ISOLATION RELAYS
RC/
RH
W
Y
G
HEAT = R to W
COOL = R to Y
WIRES FROM HVAC TO THERMOSTAT
FAN = R to G
C
R
W
Y
G
HEAT RELAY
COOL RELAY
FAN RELAY
115VAC
P
S
24VAC
24VAC TRANSFORMER
TYPICAL HVAC SYSTEM
H
EATER
COMPRESSOR
FAN
8
9
24VAC HEAT, FAN and COOL 5 wires (with separate heat & cool power)
The drawing below is a standard 24VAC, 5 wire heat and cool controls system. Some
times, the heating and cooling systems have their own separate 24VAC power so there
are two power sources, RC (cool and fan) and RH (heat).
The 24VAC HEAT transformer provides power to just the HEAT relay. The 24VAC
COOL transformer provides power to the FAN relay and the COOL (compressor) relay.
When there are two power sources, the strap between RC and RH must be removed or
damage may occur! The RC wire and the RH wire must never touch each other.
It is important for the customer to turn off his power before he disconnects the old
thermostat!
The 5 wire heating and cooling functions are the same as the 3 and 4 wire drawings. Note
when there are two transformers, the C wire comes from the HEAT transformer.
TYPICAL 24VAC, 5 WIRE HEATING & COOLING SYSTEM
FAN = RC to G
COOL = RC to Y
HEAT = RH to W
RC
RH W
Y
G
THERMOSTAT
RC
C
RH
W
Y
G
HVAC
P
S
P
S
24VAC
24VAC
COOL 24VAC
HEAT 24VAC
HEAT RELAY
COOL RELAY
FAN RELAY
FOR FIVE WIRE, FORCED AIR, 24VAC HEATING AND COOLING SYSTEM
GAS, OIL, ELECTRIC
9
10
24VAC TWO STAGE HEAT AND SINGLE STAGE OF COOL 5 WIRES
The drawing below is the wiring of a typical two stage heating system and not a heat
pump. From a setback of over 2F, when heat is requested by our thermostat, the first
stage comes on and after 1 minute the thermostat turns on the 2nd stage of heat which also
increases the fan speed. Both stages stay on all the way to target and then both stages
shut off. This allows much faster recovery from a set back. After that the 1st stage
generally can maintain the room temperature which is more efficient and quieter.
However if the room temperature drops below the “differential” (typically -2F) below
the room temperature because the first stage cannot keep up, then the 2nd stage again
comes on with the 1st stage and both run all the way to target. Also, if the customer wants
to increase the room temperature faster, when he turns the target up over 2F above the
room temperature, he gets more heat faster as the 2nd stage comes on all the way to the
new target.
Some other thermostats do not turn on the 2nd stage for 15 minutes after the 1st stage
comes on which slows down recovery.
FIVE WIRE, FORCED AIR, 24VAC, 2 STAGE OF HEATING AND SINGLE STAGE OF COOLING
W2
RC RH W
Y
G
FAN = RC TO G
COOL = RC TO Y
1ST STAGE HEAT RH TO W
2nd STAGE HEAT RH TO W2
C
W2
R
W
Y
G
P
S 24VAC
2N
D STAGE HEAT
1ST STAGE HEAT
COMPRESSOR
FAN
RELAY
RELAY
RELAY
RELAY
SYSTEM COULD HAVE 6 WIRES IF THE HVAC SYSTEM HAS SEPERATE RH AND RC
10
11
24VAC HEAT PUMP WITHOUT AUXILIARY HEAT 4 WIRE
The drawing below is a heat pump without auxiliary heat. This is useful with an air heat
exchanger (outside unit) in mild climates like Florida and parts of Arizona. If the heat
exchanger is in the ground or in a well (hydro), it is very efficient and auxiliary heat is
not necessary.
Notice the thermostats W (heat) and Y (cool) are connected together. This is because the
compressor is used when the thermostat calls for heating (W) or cooling (Y). The
terminals O or B control the changeover relay which determines if it will be heating or
cooling.
Heat pumps do not control the fan; thermostats used for heat pumps must have the
GAS/ELECT jumper in the ELECT position.
In a heat pump, never connect both O and B or damage may result. See wiring pg 3.
NOTE: Some heat pumps use other letters for the changeover. Florida Heat Pump Co.
uses the letter W on the old thermostat instead of O. (Connect their W to the stats O)
For more information about heat pumps go to: www.dhclimatecontrol.com/hp.htm
TYPICAL 24VAC, HEAT PUMP WITHOUT AUXILIARY HEAT
FAN = RC TO G
COOL= RC TO Y
HEAT = RH TO W
CHANGE OVER RH/RC to O or B (not both)
RC O B RH W
Y
G
O or B
NOT BOTH
C
O
B
R
Y
G
O or B
P
S24VAC
REVERSING
CHANGEOVER
COMPRESSOR
FAN
VALVE
RELAY
RELAY
RELAY
FOUR WIRE, FORCED AIR, 24VAC, HEATING/COOLING HEAT PUMP WITHOUT AUXILIARY HEAT
11
12
24VAC HEAT PUMP WITH AUXILIARY HEAT 5 WIRE
The drawing below is a heat pump with auxiliary heat. The auxiliary heat is usually
electric heat strips mounted on the air output of the heat pump. This type of system is
typically used where there is no natural gas available in cool to cold climates.
From a set back of over -2F our thermostats turn on the heat pump and after 1 minute turn
on the aux electric heat. Both stay on all the way to target for fast recovery and then both
shut off. The heat pump will then attempt to maintain the target room temperature. If the
heat pump cannot keep up because the outside temperature is too cold, when the room
temperature drops below -2F, the electric aux heat comes on with the heat pump all the
way again to target. If the heat pump quits, the aux electric heat will still keep the room
temperature within 2F of room temperature.
However, the auxiliary heat can also used by itself if the heat pump quits or just can’t
keep up. When the thermostat is switched to AUX HEAT ONLY the heat pump is shut
off and only the AUX heat is used and will maintain the target temperature.
Heat pumps do not control the fan; thermostats used for heat pumps must have the
GAS/ELECT jumper in the ELECT position.
TYPICAL 24VAC, HEAT PUMP WITH AUXILIARY HEAT
W2
RC O B RH W
Y
G
FAN = RC TO G
COOL= RC/RH TO Y/W (Changeover in COOL)
O or B
HEAT = RC/RH TO Y/W (Changeover in HEAT)
NOT BOTH
AUX HEAT = RC/RH TO W2
CHANGEOVER = RC/RH to O or B (not both)
C
W2
O
B
R
Y
G
O or B
P
S24VAC
AUXILIARY
REVERSING
CHANGEOVER
COMPRESSOR
FAN
HEAT
VALVE
RELAY
RELAY
RELAY
If the heat pump AUX HEAT is gas or oil it is installed at the air input side of the heat
pump and cannot run when the heat pump is running or it would overheat the heat
exchanger. So if the thermostat is set for GAS/OIL AUX HEAT, the thermostat will shut
off the heat pump when the aux heat comes on. The heat pump is used for maintaining
room temperature and the gas or oil aux heat is used for recovery.
12
13
24VAC ZONED FORCED AIR HEATING AND COOLING 6 WIRE (main)
The drawing below is a forced air, zoned, heating and cooling system with remote
thermostats for different areas. The master control unit opens and closes baffles in the
forced air system to open an area or close an area for either heating or cooling. This
allows different areas of the house to be at different temperatures as a function of the
areas own thermostat using a single HVAC system.
The selection of HEATING or COOLING is made by the master controller. If the
customer wishes to use programmable thermostats at the remotes, they must remember to
switch the remotes from HEAT to COOL whenever they switch the main thermostat from
HEAT to COOL. This is because the heating and cooling programs are different.
Some forced air zoned systems master controllers use both B and O for changing from
HEAT to COOL and some use just one of the letters, B or O. Be sure it is a gas forced air
zoned system before connecting both O and B.
Some of the names of forced air zoned heating are Durazone, Trol-a-temp.
ZONE FORCED AIR HEATING AND COOLING (such as Trol-a-temp)
REMOTE THERMOSTAT
STRAP
MAIN THERMOSTAT
C RC O B RH W Y
G
A
RC
RH W Y
STRAP
O
B
R
W
Y
G
MASTER CONTROL UNIT
FOR SELECTION OF HEAT OR COOL
AND ZONE BAFFEL CONTROLS
STRAP
RC
RH W Y
REMOTE THERMOSTAT
NOTE: Be sure your system is not a heat pump before connecting O and B.
Connecting both O and B in a heat pump, can cause damage to the HVAC system.
13
14
ZONE HOT WATER HEATING SYSTEMS
(3 wires to thermostat)
The drawing below is a zoned hot water system that uses a 3 wire thermostat control
system to open and close a rotary valve or a solenoid valve.
NOTE: If a hot water system has just two wires, connect it as a standard 2 wire
heating system between RH and W.
ROTARY VALVE
When the thermostat requests heat, RH connects to W and the rotary motor controlled
valve opens. When the thermostat requests the heat go off, the RH to W connection opens
and the RH to A connects and the rotary motor controlled valve closes. Each valve has a
switch to turn the boiler on and off so the boiler can be turned on by any zones rotary
switch.
SOLENOID VALVES (note reverse wiring from rotary connections)
When heat is not requested, RH is connected to A and holds the solenoid valve in the
OFF position (powered off). When heat is requested, RH disconnects from A which lets
the solenoid go and its spring opens the valve. At the same time, RH connects to W and
turns on the boiler. Any zone’s thermostat can turn on the boiler. If the valve or its power
fails, the valve springs open and allows some heating by convection.
Rotary
Solenoid
CONNECTION FOR MOTOR CONTROLLED VALVES
CONNECTION FOR SINGLE SOLENOID VALVE
N
/C
N/C
REMOTE THERMOSTAT
REMOTE THERMOSTAT
HEAT RELAY
N
/O
HEAT RELAY
N/O
RH
W
A
RH
W
A
C
C
R or 5
W or 4
Y or B or 6
R
Y or B
W
BOILER CONTROL
SPRING
VALVE OPEN
VALVE SHUT
SOLENOID
P
S24VAC
24VAC
P
S
VALVE OPEN
VALVE SHUT
MOTOR CONTROLLED VALVE WITH SWITCH
NOTE VALVE IS POWER OFF SO TERMINAL "A "
14
15
RV’s, 2 speed fan’s, and Swamp Coolers
24VAC CONTROL RV A/C
12VDC CONTROL RV A/C
12VDC CONTROL RV PROPANE HEATER
12VDC CONTROL RV PROPANE HEATER
ALTERNATE
RH
W
RC Y G
RC RH W
Y
G
FAN
THERMOSTAT
CONNECT
THERMOSTAT
R or PWR
or GND
Y or A/C
G2, F2, H
R or GROUND
CAP OFF
Y or A/C
G2, F2, H
W or FURN
RC
G, G1, F1
W or FURN
7.5V
G, G1, F1
PROPANE FURNACE
AIR CONDX
BATTERY - (gnd)
BATTERY - (gnd)
PROPANE FURNACE
AIR CONDX
CONNECT G2 TO G FOR HIGH FAN
REMOVE THE THERMOSTATS GAS/ELEC
JUMPER AND USE AUTO/ON FOR FAN SPEED
All RV air conditioners run on 115VAC and the RV must be connected to AC power for
the air conditioner to operate. No Air Conditioning test can be done with out AC power.
SWAMP COOLERS
Swamp coolers connect like any A/C system (RC, Y, and G). If there is a two speed fan,
connect just the G fan wire to the thermostats G terminal for low, or both fan wires (G
and G2) for high. The alternate fan connection above right allows the use of the
thermostats fan AUTO/ON switch to be a LOW (auto) and HIGH ( on) manual switch.
Do not use a 24VAC thermostat for a line voltage swamp cooler.
MOBILE HOME
Some mobile homes have a 2 wire thermostat for heating and cooling. The
HEAT/OFF/COOL switch is on the side of the HVAC system. Typically in this case,
connect the two wires going to the thermostat to RH and W.
Leave the thermostat always in HEAT; do not switch the thermostat to cool.
C RC O B RH W
Y
G
THERMOSTAT
MODE SWITCH ON UNIT
H
C
OFF
115VAC
P
S
24VAC
HEAT RELAY COOL RELAY
MOBILE HOME WITH MODE SWITCH ON SIDE OF HVAC UNIT
15
16
LINE VOLTAGE THERMOSTATS
NOTE: Line voltages are very dangerous and the power to the heating system
should be shut off before changing the thermostat! These are typically used for
baseboard, wall, ceiling and floor heating systems.
LINE VOLTAGE DOUBLE POLE (4 large wires)
The DOUBLE POLE type will have 4 large wires coming out of the thermostat. To
connect to 4 large wires coming out of an electrical box in the wall. Do not connect a
24VAC thermostat to line voltage or severe damage will occur to the thermostat.
DOUBLE POLE: BOTH SIDES OF POWER GO THROUGH THE THERMOSTAT
LINE VOLTAGE THERMOSTAT
THERMOSTAT
WIRE
NUTS
BLACK
BLACK L1
RED
T1
FROM BREAKER BOX
LINE IN
LOAD TO HEATER
HEATING ELEMENT
WHITE
BLACK
L2
RED
T2
POWER ON/OFF SWITCH IN THERMOSTAT
MAX RATING AT 230VAC AT 16 AMPS (about 3680 Watts)
MAX RATING AT 115VAC AT 16 AMPS (about 1840 Watts)
LINE VOLTAGE SINGLE POLE HEATING (2 large wires)
The SINGLE POLE type will only have two large wires coming out of the thermostat.
SINGLE POLE: JUST ONE SIDE OF THE POWER GOES THROUGH THE THERMOSTAT
THE OTHER SIDE OF THE POWER GOES DIRECTLY TO THE HEATING ELEMENT
THERMOSTAT IN HEAT
THERMOSTAT
WIRE
NUTS
RED TO LOAD
WHITE
BLACK TO LINE
BLACK
BLACK
FROM BREAKER BOX
LINE IN
HEATING ELEMENT
WHITE
MAX RATING AT 230VAC AT 16 AMPS (about 3680 Watts)
MAX RATING AT 115VAC AT 16 AMPS (about 1840 Watts)
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LINE VOLTAGE SINGLE POLE COOLING (2 large wires)
Some line voltage thermostats can be used for heating OR cooling as below. They will
have a switch to select HEAT OR COOL (not both).
CONNECTION FOR LINE VOLTAGE COOLING THERMOSTAT (SWAMP COOLER ETC)
THERMOSTAT IN COOL
THERMOSTAT
WIRE
NUTS
RED TO LOAD
WHITE
BLACK TO LINE
BLACK
BLACK
FROM BREAKER BOX
LINE IN
COOLING DEVICE
WHITE
MAX RATING AT 230VAC AT 16 AMPS (about 3680 Watts)
MAX RATING AT 115VAC AT 16 AMPS (about 1840 Watts)
CONTROLLING HUMIDITY (Thermostat equipped with a built humidistat)
HUMIDIFIER
If you have a humidifier and wish your thermostat with a built in humidistat to control it,
connect the humidifier as shown below. The MIN (minimum) humidity setting on the
thermostat will now turn the humidifier on and off as a function of the humidity level in
your home.
If the humidistat is set for ALWAYS, when humidity is requested by the humidistat, the
humidifier and the fan will be turned on until the humidity is at the target (about +/- 5%).
If the humidistat is set for WITH HEAT ONLY, the humidifier will not come on until
there is both a request for heat and a request for humidity at the same time. When either
heat or the humidistat is satisfied and shuts off, the humidifier will shut off.
NOTE: If your thermostat has a built in humidistat (with an H terminal), and your heating
system has a built in humidifier, connect it as below using the HVAC 24VAC power.
RH
H
R
P
S
115VAC
HEAT 24VAC
HUMIDIFIER RELAY
C
FURNACE TRANSFORMER
HUMIDFIER CONNECTION USING THE HEATING SYSTEM 24VAC
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NOTE: If your heating system has an added humidifier with its own separate 24VAC
connect it as below.
RH
H
R
OPTIONAL " FAN RUNNING" SWITCH
115VAC
P
S
HEAT 24VAC
C
HUMIDIFIER RELAY
FURNACE TRANSFORMER
24VAC
EXTERNAL 24VAC WALL ADAPTER
HUMIDIFIER WITH EXTERNAL 24VAC ADAPTER
CONNECTING AN EXTERNAL HUMIDISTAT FOR HUMIDIFING
If you have an existing humidifier, with an external humidistat, and wish it to be active
only when the thermostat is switched to HEAT, connect the power wire (R) from your
humidistat to the B terminal of your thermostat (if it has one).
When the mode switch is put in HEAT, the B terminal is powered from the RH terminal,
which will power the external humidistat. The humidistat will then operate independent
of the thermostat settings. When the thermostat is switched to OFF or COOL, the external
humidistat will be off.
HUMIDIFIER CONNECTION WITH AN EXISTING EXTERNAL HUMIDISTAT
B
RH
W
THERMOSTAT
POWERED IN HEAT ONLY
EXTERNAL
HUMIDSTAT
H
C
RH
W
HVAC
P
S 24VAC
HUMIDIFIER RELAY
H
EAT 24VAC
HEAT RELAY
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DE-HUMIDIFYING (humidistat using the air conditioner)
Some thermostats internal de-humidifier can use an air conditioner for de-humidifying or
can use an external dehumidifier (DH terminal). The A/C can be used for de-humidifying
or cooling, or can be set up to dehumidify only when also cooling is also required.
DE-HUMIDIFYING USING AN EXTERNAL DE-HUMIDIFIER
If a system has an external de-humidifier unit, it de-humidifies but is temperature neutral
so does not add cooling to the house. If your thermostat as a humidistat that can use an
external de-humidifier (DH terminal) then it can be connected as below using the cool
24VAC power source.
CONNECTION WITH AN EXTERNAL DE-HUMIDIFIER
USING HVAC 24VAC POWER
DH
THERMOSTAT
RC
Y
EXTERNAL
DE-HUMIDIFIER
RC
Y
HVAC
COOL
P
S
115VAC
POWER
COOL RELAY
If a system has an external de-humidifier unit, it de-humidifies but is temperature neutral
so does not add cooling to the house. If your thermostat as a humidistat that can use an
external de-humidifier (DH terminal) then it can be connected as below using a separate
24VAC power source.
CONNECTION WITH AN EXTERNAL DE-HUMIDIFIER
USING SEPERATE 24VAC POWER
DH
THERMOSTAT
RC
Y
EXTERNAL
DE-HUMIDIFIER
RC
Y
HVAC
115VAC
P
S
24VAC
COOL RELAY
24VAC ADAPTER
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CONNECTING AN EXISTING HUMIDISTAT FOR DE-HUMIDIFING
NOTE: The power to the external humidifier should come from the thermostats O
terminal which is powered only in the cool mode so the HEAT and the A/C cannot be on
at the same time.
PARALLEL: The air conditioning can be turned on by either the humidistat with high
humidity over its target or by the thermostat because of high temperature over its target.
DE-HUMIDIFIER CONNECTION WITH AN EXISTING EXTERNAL HUMIDISTAT
PARALLEL: EITHER HIGH TEMPERATURE OR HUMIDITY WILL TURN ON THE AIR CONDITIONER
RC
O
Y
EXTERNAL
HUMIDISTAT
RC
115VAC
P
S
24VAC
COOL RELAY
SERIES: The air conditioning will come on only with high humidity over its target and
high temperature over its target.
DE-HUMIDIFIER CONNECTION WITH AN EXISTING EXTERNAL HUMIDISTAT
BOTH TEMP AND HUMIDITY MUST BE ABOVE TARGET TO TURN ON A/C
RC
THERMOSTAT
Y
EXTERNAL
HUMIDISTAT
RC
Y
115VAC
P
S
24VAC
COOL RELAY
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THERMOSTAT POWER
BATTERIES
Some thermostats are powered from batteries. The life of the batteries is typically
between 1 and 2 years depending on how often the backlight is used.
DO NOT USE RECHARAGLE BATTERIES (voltage to low to run)
If the batteries die, the thermostat will quit operating with the HVAC off. The LOW
BATTERY icon will come on for several weeks before this happens. When changing
batteries do it quickly (30 seconds) or you may lose your time and custom program
settings. The thermostat will still function and default to the built in Energy Star
program, but would still need to have the day and time re-set. All manual functions will
continue to work.
24VAC POWER
Some thermostats can also use the 24VAC heat power if available. One side of the
24VAC is the power wire at the thermostat going to the RH terminals. The other side of
the 24VAC is called the “C” wire and if available at the thermostat, can be connected to
the thermostats C terminal. This will allow the thermostat to get its power from the
furnace so the battery life will about double. Thermostats with a backlight will have the
backlight also be powered from the 24VAC power. If you have a wire you think is the C
wire, a test is to measure the AC voltage as follows:
1. Connect the RH and W terminals with a piece of wire or a paper clip. Doing this turns
on the heat.
2. Between the proposed C wire and the RH wire terminal should be about 24VAC to
28VAC with the heat on.
The batteries are still necessary to retain the thermostats custom programs and other
settings if the AC power to the furnace is interrupted. Using the 24VAC (C wire), the
thermostat will continue to run if the batteries die. The C wire is shown in all of the heat
connection drawings. If there is an unused wire in the wall, an HVAC tech can connect it
for you or run another wire.
THERMOSTATS WITH RADIOS AND/OR REMOTE CONTROL (require C
wire)
Thermostats with remote control must have the 24VAC for the remote’s receiver inside
the thermostat to work. The remote receiver in the thermostat requires power and would
substantially reduce battery life so cannot run on the batteries.
If the C wire is not readily available, a 24VAC plug-in power adapter may be used by
connecting its wires to the thermostats terminals RH and C. There is no polarity of the
two wires so either wire can go to either terminal. The Radio Shack Cat No. 273-1690
adapter can be used. Cut off its connector and connect the two wires to RH and C; put its
switch on 24VAC.
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FAN CONTROL
MANUAL (auto/on)
The normal position for the fan switch is AUTO which allows the fan to be
controlled by the furnace or by the thermostat as explained below. In the ON
position, the fan will run continuously. This can keep your house at a more even
temperature and if you have a good clean air filter system can reduce dust and smells.
HEATING (gas/electric selection)
Most forced air heating systems that use gas or oil has their own fan control. When the
heating system is hot enough its “stack” upper limit temperature switch turns on the fan.
When the house is up to temperature, the thermostat shuts off the burner, the stack cools
down, and the furnace’s lower limit temperature switch shuts off the fan. These limits
switches control the fan when the thermostats gas/elect jumper selector is in GAS.
Electric heating systems can also have fan control as above but most do not and rely on
the thermostat to turn the fan on and off with the electric heat. Electric heat should not be
turned on without air circulating over the heater elements. For electric furnaces and heat
pumps, the thermostats fan control jumper selector (gas/elect) should be set in the
ELECT position. When the thermostat is controlling the fan, it may have additional
capabilities such as leaving the fan run 1 min after the heat goes off (purging) or the
option of having the fan run a minimum of 5 minutes per hour for better air circulation.
COOLING
Air conditioners (AC) do not have internal fan control and require the thermostat to turn
the fan on and off with the compressor. Your thermostat does this as long as the
GAS/ELECT jumper is in either GAS or ELECT. Some AC systems control the fan
separate from the thermostat. These newer units turn the fan on with the compressor, and
then leave the fan running for a while after the compressor has shut off. This is more
efficient by clearing out the residual cool air after the compressor has shut off.
When the thermostat is controlling the fan, it may have additional capabilities such as
leaving the fan run 1 min after the cool goes off (purging) or the option of having the fan
run a minimum of 5 minutes per hour for better air circulation.
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GENERAL INFORMATION
SWING
Swing is the temperature difference between where a system comes on and then goes off.
Most programmable thermostats have the ability to set the swing.
EXAMPLE: The thermostat is set at HEAT, a target temperature set at 70F, and the
swing is set at 1F. The heat would typically come on at 71 and go off at 69.
The lower number gives a higher comfort level as the room temperature is more constant
and the HVAC system will cycle more often. The higher number is more efficient and the
HVAC system will cycle less often.
ANTICPATORS
Mechanical thermostats use anticipators. This is a resistive device that heats up when the
thermostat has turned on the heat. The anticipator gets warm; heating the thermostat so
that it will shut off the heating system earlier than it would have without the anticipator.
This is done because there is a delay in the reaction of the thermostats temperature sensor
spring due to the thermal mass of the mechanism. The typical swing in a mechanical
thermostat can be wide and get wider with age. Anticipators are not necessary in
electronic thermostats because the mass of the temperature sensor is very small.
ELECTRONIC THERMOSTATS ACCURACY
Most thermostats are specified and checked at +/- 1F. The room temperature measured
by the thermostat is a function of the room, wall, and radiant temperatures near the
thermostat. For better accuracy, fill the hole in the wall with insulation so the thermostats
room temperature will not be affected by air flow in the wall. When you are installing a
thermostat, the room temperature will initially read high because the case has been
warmed by your hands. It may take several hours for the thermostat to stabilize to room
temperature. If your new thermostat does not match you old thermostat, the error is
probably a combination of the two thermostats accuracy. Some thermostats allow you to
change or “calibrate” the room temperature to match another device, or to set it for a
comfort level in a different room.
CALIBRATION (if the thermostat has room temp set)
If you wish to have the room temperature reading on your thermostat match some other
device, use the units calibration function.
The (delta sign) T-FACTOR means the change in room temperature setting when you
“calibrate” the room temperature to your liking. When you change the room temperature
with the “calibration” function, the display shows you both the new room temperature
and the T-FACTOR which is how much you changed the room temperature display.
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COMPRESSOR DELAY
Most electronic thermostats with cool or heat pump capability have a build in approx 4
minute delay from the time a compressor turns off until the thermostat can turn it back
on. This is allows the unit to de-compress which prevents compressor stall.
1. If a customer has his compressor running (heat or cool) and changes his target
to shut it off, then within 4 min decides to turn it back on, it will not come on until
the end of the delay.
2. The delay can be terminated by switching to OFF and back on. Do not do this if
the compressor has been running; wait 4 minutes before turning it back on.
3. Always reset with mode switch in OFF.
4. If connected to a C wire, the delay occurs if AC power is lost and then restored.
5. There is no delay in NORMAL HEAT.
DIFFERENTIAL (2 or more stages of heat and/or cool)
When the room temperature is below the target temperature by more than the differential,
the next stage will come on with the 1st stage all the way to room temperature. Then the
1st stage will attempt to maintain the room temperature by itself. If the room temperature
goes below the differential again the next stage will come on. A typical differential may
be over -2F for heat and over +2F for cool.
RESET
The thermostats reset button should be pushed after initially putting in the batteries. It
should also be pushed if any set up is changed using the little jumper. Reset restores
factory settings including the program which goes back to the EPA Energy Star.
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TROUBLE SHOOTING
The thermostat simply connects the wires coming to the thermostat together as needed to
control a given function. The thermostat uses an isolated relay that makes these
connections. The thermostat does not have, or generate any power, it simply switches the
power (RC and RH) coming to the thermostat to the appropriate control wires for heat
(W), compressor (Y), fan (G) etc.
FAN CHECK
RC is used as power for the fan and G is the fan return wire. Connecting RC to G should
turn the fan on. If it does not the problem is in the fan system. This may indicate the low
of the 24VAC power.
HEAT CHECK
RH is power for the heat and W is the heat return wire. Connecting RH to W with a wire
or paper clip (used as a wire) should turn the heat on in either 24VAC or GAS millivolt
systems. If the heat does not come on, the problem is in the heating system.
COMPRESSOR CHECK
RC is used as power for the cooling compressor and Y is the compressors return wire.
Connecting RC to Y should turn on the cooling compressor (outside unit).
WARNING: When checking the compressor, DO NOT shut if off and right back on.
After it has been on and then off, wait for 4 minutes before turning it on again to prevent
compressor stall.
24VAC POWER CHECK
In a 24VAC system, if nothing works, the 24VAC power may be off. This can be
because of lack of main power to the heating system (check breakers), or a blown fuse on
the 24VAC line. To check for the 24VAC power, use an AC voltmeter and measure
between the RH and the W terminals with the heat off; there should be 24 to 28VAC.
TESTING FOR SHORT CYCLING (heat cycling on and off)
If you’re heating system sounds like it is cycling on and off too often, try increasing your
SWING setting on your thermostat. Another check is to connect the RH terminal to the
W terminal with a wire. This will turn on and hold on your heat as long as RH is
connected to W. If the furnace still short cycles the problem is in the furnace. The
problem could be your heating system’s stack switch settings that control the fan or a
clogged air filter.
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TESTING FOR LONG CYCLING (Furnace or AC runs almost continuously)
If your HVAC system is running continuously and the room temperature is not changing,
the problem may be the HVAC system cannot keep up with the heating or cooling
settings because of outside temperature extremes. If the room temperature never gets to
or crosses the target temperature setting the thermostat is not going to shut the HVAC off.
Again, check your air handler filters.
HEAT: Lower your target temperature 5F below your room temperature, the furnace
should shut off in a few minutes which indicates the thermostat is working.
COOL: Raise your target temperature 5F above your room temperature, the cool should
shut off in a few minutes which indicate the thermostat is working.
FAN NOT RUNNING IN COOL
In cool if the fan comes when the thermostat fan switch is moved to ON, but the fan does
not come on when the compressor starts, check to see if the GAS/ELEC selection is on
gas or elect. It must be in gas or elect for the thermostat to control the fan in cool.
THERMOSTAT RANDOMLY RESETS
If your electronic thermostat randomly resets back to its original settings and time, it may
be caused by radio frequency interference (RFI) or RF noise. This is more prevalent in
gas furnaces with spark igniters that are close to a digital thermostat. If this occurs, the
RFI can be reduced and/or eliminated by adding an RF chock on the leads going from the
furnace to the thermostat. This is very easy to do.
The Radio Shack ferrite data line filter cat # 273-105 is a clip on device the goes around
all the wires going to the thermostat. It is best to put it at the furnace end if easy to get to,
but may also be used on the wires at the thermostat end. In some cases, one at each end
is even better. If the wires are too large for that filter, the Radio Shack snap on RF chock
cat #273-104 may be used.
TRANE HEAT PUMP B WIRE
Some systems built by Trane do not use the NEMA standard for the “C” (power
common) wire. They use a wire labeled “B” for the common power wire. If both the O
wire and the B wire are present on a Trane product heat pump, connect the O to O but do
not connect the B wire to the B terminal or damage to the 24VAC power will occur.
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SAFETY
LINE VOLTAGE THERMOSTATS
Always shut off the power at the breaker box before wiring any thermostat. If you have
line voltage heating or cooling, be sure to use a line voltage thermostat. Connecting a line
voltage thermostat to a low voltage 24VAC thermostat is dangerous and will damage the
thermostat. All line voltage thermostats have large wires coming out of the thermostat
and connect to large wires in an AC box with large wire nuts.
24VAC
If the power wire (R, or RH or RC) touch the power common wire (C or X) damage to
the 24VAC power will occur. Never connect the C wire to any other wire.
If you have separate heat (RH) and cool (RC) power wires do not let these wires touch
each other. Also, if you have both RC and RH wires, be sure to remove the jumper wire
between RC and RH before connecting any wires.
If you have a heat pump with both O and B wires, it is probably a Trane product and the
O should be connected to O but the B should not be used until you are sure it is the power
common wire. Then it can be connected to the thermostats C terminal.
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