Need help picking a new thermostat and wiring


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Old 04-27-14, 12:10 PM
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Need help picking a new thermostat and wiring

Hello everyone and thanks in advance for any suggestions/assistance that anyone can give me. I live in an older house that has a what I guess to be quite old thermostat with two mercury switches inside of it, I have come to the conclusion that it is time to modernize this thermostat as it seems to run full time more often that not. I need help figuring out which thermostat I should purchase from home depot as I believe it is a heat pump system, here are the current wiring letters that are on the inside of the thermostat, as I cannot see the backside I don't know if all of them are hooked up but I believe they are.

F, B, G, X2, Y W T O R

What I basically need is ideas on what thermostat to buy, honeywell most likely and which terminals will be used for these old wires.

Thanks
 
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Old 04-27-14, 12:49 PM
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It is unlikely that your longer run times are due to the thermostat.

Post the make and model of your old stat.

The Q674x- xxxx number would be great, an LRxxxx will not work.
 
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Old 04-27-14, 12:54 PM
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It's a GE Weathertron, numbers on the inside are T91H110M183 and AY28X078

I would like to update it either way, from my understanding about how these older ones work if those mercury filled tubes aren't in perfect alignment it can keep the system from shutting off right?
 
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Old 04-27-14, 01:03 PM
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Yes the mercury thermostats must be level to correctly operate,

Your old stat B terminal is C on any new thermostat. Do not connect it to the new B terminal.

http://i151.photobucket.com/albums/s...04/Baystat.jpg

What features are you looking for in a new stat?
Wifi? Programmable?
 
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Old 04-27-14, 02:09 PM
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I guess a wifi thermostat would be nice, since it's going to reside in a room I won't always have access to. Looking at the Honeywell one on home depot RTH6580WF it says it needs a C wire which the current system does not have, does that mean I would have to somehow run a wire to the unit?
 
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Old 04-27-14, 02:34 PM
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Yes the wifi models need a common wire.
Do you have a wire connected to the B terminal at this time?

If you do, you have common.
 
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Old 04-27-14, 02:53 PM
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It has a screw in it, so I'm guessing that there is a wire connected to it, let me attach a picture of the thermostat with the cover off.

http://i117.photobucket.com/albums/o...427_145118.jpg
 
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Old 04-27-14, 03:30 PM
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Turn off power to the indoor unit and remove the stat to see the connections.
 
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Old 04-27-14, 07:05 PM
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Not quire sure if it has one or not, not sure how that stat is even mounted to the wall, don't see any screws in it, took the screw out for B and doesn't appear to be anything attached to it.
 
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Old 04-27-14, 09:32 PM
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You are correct wiring indicates heat pump. If heat pump stats are available at home depot White Rogers, Robert shaw, or honeywell. These are industry best and most dependable. Be sure to secure all power before removing old stat. You cross wires 1 time and could short out 12/24 transformer. Grainger Industrial Supply - MRO Products, Equipment & Tools has full line of all mentioned stats or local reputable H.V.A.C. supply shop should have in stock.
 
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Old 04-28-14, 11:03 AM
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I have one final question, this is an upstairs thermostat, and there is an air handler behind the wall in an attic almost directly behind the thermostat. If there is no common wire connected to the B terminal, would I be able to run a wire to the air handler to provide power to the new thermostat? If it's that simple what kind of wire do I need to get, and I will try to take pictures of the handler so someone can point out to me where to attach it on the handler. A side note, there is the main unit downstairs in a closet, and there is a sheaf of wires that comes up through the floor from that unit, to the handler up here then another branch off that comes from that to the other thermostat, so I'm assuming I could attach a common wire to the unit upstairs.
 
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Old 04-28-14, 11:10 AM
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Old 04-28-14, 03:21 PM
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Here are a couple of pictures of the wires going to the back of the thermostat, I'm guessing one of them sends power, since this doesn't have batteries? I just don't know if it goes to B which would go to C on a modern thermostat.

http://i117.photobucket.com/albums/o...428_131744.jpg

http://i117.photobucket.com/albums/o...428_131752.jpg
 
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Old 04-28-14, 07:41 PM
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I do not see the wire connections in any of your picture.
If you cannot figure out how to remove the stat I recommend calling a pro.
 
 

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