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Gas Heat
THERMOSTATS
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Thermostat
• A thermostat is a control
that is activated by
changes in the
surrounding air temp.
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Mercury thermostat
• Has mercury inside which is
considered a hazardous material
which.
• Mercury was used because it stays
liquid at room temperature.
• Not as sensitive as a programmable.
• Has a heat anticipator.
• Can only set 1 temperature at a
time.
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Mercury Bulb Thermostat
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Snap Action Thermostat
No mercury.
Inexpensive.
Accurate, but not as sensitive as a
digital thermostat.
Has a heat anticipator.
Can only set 1
temperature at a time.
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Snap Action Thermostat
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Digital Thermostats
• No mercury inside.
• Operated by a circuit board
and sensor.
• More sensitive to temperature
change- up to ½ a degree.
• Depending on the brand and
model of t-stat being
installed, you can set more
then 1 temperature.
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Common wiring terminals on all basic
thermostats
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RC = 24v power for cooling
RH = 24v power for heating
Y = cool
W= heat
G = blower
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Common wiring terminals on all
higher end thermostats
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RC/RH= power (24v)
Y1= stage 1 cool
Y2= stage 2 cool
W1= stage 1 heat
W2= stage 2 heat
G=fan
O= reversing valve ( found on heat pumps)
C= common
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Common wire colors used for wiring
components
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RC/RH = Power (24v) = red
G = Fan= green
Y1 = stage 1 cool= yellow
Y2= stage 2 cool= blue
W1= stage 1 heat= white
W2= stage 2 heat= brown
O- reversing valve= orange
C = Common= black
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Heat anticipator
• A device that will shut
down the heating circuit,
prematurely of the set
point, so the system does
not over shoot the setpoint temperature.
• The set-point is the
temperature the
thermostat is set too.
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Setting a heat anticipator
• Take your meter to the t-stat and set it to amps.
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Jump out your heating circuit (R and W)
Wrap your jumper around your amp probe 10 times
Read your meter and divide by 10
This is your heat anticipator set-point
• Sometimes this information can be written on unit
information sticker.
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Symbols
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