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Old 05-20-2013, 06:45 PM   #1
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thermostat wiring


hi! new to forum. hope i'm not breaking any rules!

i'd like to hook my thermostat up to the internet (i know about the NEST but i'm going the diy route). i'm going to be using a raspberry pi and a relay bank to replace the stock thermostat. i've been googling around and doing research about the wiring to the stock thermostat. but i haven't been able to quite figure out what each terminal, that actually has a wire going into the wall, does and which ones get "activated" when i tell the thermostat, stock one, to heat or cool or auto or w/e.

here's a picture of the thermostat:



i've looked for a manual online but i can't find anything. specifically i don't know what happens with the O and B and W2 terminals. i know that O and B are for energizing the 4 way valve for cooling or heating or vice/versa but i don't know when in the cooling or heating cycle that happens? does that happen as soon as the system wants to cool/heat my home? also i don't know when W2, the second stage heating, is activated.

any help anyone can give me would be much appreciated

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Old 05-20-2013, 06:52 PM   #2
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thermostat wiring


o and/or b depend on what type/brand of heat pump you have. i think Rheem/Ruud are the only ones that energize the reversing valve during heat. all else energize the valve during cool, but don't quote me on that.

r-24 volts
y-cool (1st stage, if there's two stage cooling then y2 would be second)
G-fan
w-heat
o/b-reversing valve
com- common

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Old 05-20-2013, 06:52 PM   #3
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thermostat wiring


turn the BREAKER to the furnace off before doing any stat work, always.
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Old 05-20-2013, 06:54 PM   #4
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Originally Posted by Doc Holliday View Post
o and/or b depend on what type/brand of heat pump you have. i think Rheem/Ruud are the only ones that energize the reversing valve during heat. all else energize the valve during cool, but don't quote me on that.

r-24 volts
y-cool (1st stage, if there's two stage cooling then y2 would be it.
G-fan
w-heat
o/b-reversing valve
com- common
man that was fast. so when the system goes into cooling mode both the Y terminal and O/B (whichever is for cooling) get 24V simultaneously? and what about W2?

and oh yea i know all about getting zapped and hence flipping the breaker.
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Old 05-20-2013, 07:01 PM   #5
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thermostat wiring


w2 is for second stage heat. heat pump in heating mode is first stage. if the system can not hold up on just first stage or runs too long before satisfying desired set point of the stat then second stage heat chimes in to assist. what's your second stage, gas furnace or electric air handler? or something else such as oil...???

weird thing is I'm not seeing a terminal/wire for w which would bring on the heat pump as first stage heat. not sure what's going on there.
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Old 05-20-2013, 07:21 PM   #6
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Originally Posted by Doc Holliday View Post
w2 is for second stage heat. heat pump in heating mode is first stage. if the system can not hold up on just first stage or runs too long before satisfying desired set point of the stat then second stage heat chimes in to assist. what's your second stage, gas furnace or electric air handler? or something else such as oil...???

weird thing is I'm not seeing a terminal/wire for w which would bring on the heat pump as first stage heat. not sure what's going on there.
i'm pretty sure it's an electric air handler because i'm in florida and we don't have a gas hook up. maybe W2 is just the first stage?

so i'm sorry but i'm not clear on O/B. does that kick on at the same time as the cooling unit?
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Old 05-20-2013, 07:42 PM   #7
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Originally Posted by ice109 View Post
i'm pretty sure it's an electric air handler because i'm in florida and we don't have a gas hook up. maybe W2 is just the first stage?

so i'm sorry but i'm not clear on O/B. does that kick on at the same time as the cooling unit?
if your condenser is not Rheem/Ruud then yes, the reversing valve engages during the same call for cool.

when you turn the heat on at the stat is the outdoor heat pump running, both the fan and the compressor?

also, second stage heat on a heat pump comes on during a defrost cycle that occurs on heat pumps. literally those things will become a block of ice and not be able to heat so defrost cycle kicks in, bringing on second stage and allowing the heat pump to defrost itself.
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Old 05-20-2013, 08:08 PM   #8
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if your condenser is not Rheem/Ruud then yes, the reversing valve engages during the same call for cool.

when you turn the heat on at the stat is the outdoor heat pump running, both the fan and the compressor?

also, second stage heat on a heat pump comes on during a defrost cycle that occurs on heat pumps. literally those things will become a block of ice and not be able to heat so defrost cycle kicks in, bringing on second stage and allowing the heat pump to defrost itself.
here is the diagram on the ac unit. im having difficulty reading it but i think the lower right is where it routes to the thermostat. does that help? also it's not a rheem or ruud it's the same brand is the thermostat goodman

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Old 05-20-2013, 08:14 PM   #9
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thermostat wiring


post a pic that works. use a photobucket account and use the direct link inserted into the image address bar.

geez...
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Old 05-20-2013, 08:58 PM   #10
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post a pic that works. use a photobucket account and use the direct link inserted into the image address bar.

geez...
sorry dude i figured you'd want a hirez photo so you could read all the symbols

here ya go: http://imgur.com/bpwDCrS

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