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Old 06-03-2013, 09:55 AM   #1
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Why wont 2nd thermostat kick on the AC?


My wife and I recently moved into a new home. During the inspection we noticed some strange wires sticking out of the master bedroom wall. It was discovered that the house, which was built in 2006, was wired for two thermostats, one upstairs and one downstairs. At the time we moved in only the downstairs thermostat was installed.

As we got into summer the upstairs became increasingly uncomfortable despite the downstairs thermostat being set to 72. This prompted me to buy and install the second thermostat. Besides, I didn't like the looks of the wires hanging out anyways.

I'm pretty confident that I installed it correctly and yes I did add batteries. Unfortunatley, the upstairs thermostat does not seem to trigger the AC.

I don't think the ducts are zoned, so it is my understanding that utlizing two thermostats in a single zoned system will actually result in overcooling the downstairs while making the upstaris comfortable. I'm okay with that.

I tried setting both thermostats at the same temp, having one higher than the other, and then reversed it, and I also tried turning the breaker on and off. It still doesn't work.

Why wont my second thermostat kick on the AC????

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Old 06-03-2013, 10:22 AM   #2
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Why wont 2nd thermostat kick on the AC?


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Originally Posted by mbbiggins View Post
...the house, which was built in 2006, was wired for two thermostats... I don't think the ducts are zoned...

Why wont my second thermostat kick on the AC????
Kick on what? Do you have a second furnace/AC plant that it should control?

Assuming not and assuming you're correct about no zoned ducts...
1) take the second thermostat out of the circuit
2) trace the wires to their other end
3) learn and write down what you have

Running the call for AC (or call for heat) signal through a second control can make sense sometimes. Doing it because a second set of wires are in place isn't one of them.

Some homes NEED a committee to decide that it is in fact warm enough in the house, both downstairs and upstairs, to run the AC. Or cool/warm enough both up and down for it to shut down. Is that your home?

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Old 06-03-2013, 12:51 PM   #3
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Why wont 2nd thermostat kick on the AC?


Kick on the airconditioning

I'm not sure how I could trace the wires back to their origin as they are behind drywall except for the small portion protruding from the wall.

My intent was to have a solution for a situation like this hypothetical one...the thermostat downstairs is set at 72. The upstairs is naturally warmer. Let's say 76 degress. I was hoping that by setting the upstairs thermostat to 72 degrees, the AC would turn on until the upstairs reached that temperature. I would expect the downstairs would end up being something cooler than that.

Hopefully this clarifies a bit.
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Old 06-03-2013, 03:50 PM   #4
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Why wont 2nd thermostat kick on the AC?


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Originally Posted by mbbiggins View Post
My intent was...
Your assuming that the two thermostats are interconnected...
and that this work is/was done properly.

Quote:
I'm not sure how I could trace the wires back to their origin as they are behind drywall except for the small portion protruding from the wall.
It starts by identifying each end of the wire.

The cable is probably marked (should be)... but until you know what is in the circuit and how they're all wired together (in particular how the relay is operated) ... having the second t-stat involved only complicates things.

Go back to what you knew to start the AC.
Then identify what else you have. Go from there.

hth
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Old 06-03-2013, 03:57 PM   #5
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Why wont 2nd thermostat kick on the AC?


Just based on your two posts, here are some notes:

1. It's very possible these wires you found in the master bedroom are not connected to anything on the unit. You need to check this first. Otherwise, all other work is moot. If it runs through your attic, follow it accordingly. Otherwise, it may run through the floor and runs along your joists in the basement. Regardless of how it's run, you need to figure out where those first. If you have a multimeter, see if the power wire to your upstairs thermostat has 24volts (generally the red wire) - this will tell you if it is connected or not. If there is no voltage, it may not be run to anything.

2. Double check to make sure you have it wired correctly after finding where this wire runs to.

3. If you really just want the upstairs thermostat to run the AC, with no real worry about the basement, why not just disconnect the downstairs thermostat and make your upstairs thermostat the only one? Otherwise, if your downstairs thermostat is connected to a furnace, you need to make sure that the furnace wouldn't come on if the basement reaches the required heat temperature, while your AC unit is plugging away upstairs.

Of course, you need to get more information on your upstairs thermostat first.
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Old 06-03-2013, 04:05 PM   #6
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Why wont 2nd thermostat kick on the AC?


I would just lower the temp on the main floor T-stat to 68 or 65 or whatever temp is required so that the upstairs is comfortable.

Closing some of the vents on the main floor may help with the temperature differential. It doesn't matter if you have 1 or 2 T-stats, a single zone system will always lead to overcooling the lower levels so the upstairs will be comfortable.

Why complicate it.
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Old 06-03-2013, 04:13 PM   #7
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Why wont 2nd thermostat kick on the AC?


probably aren't connected if they were hanging out of the wall.did you have an inspector when you were in contract on the place...what did he say... if you don't have 2 actual split systems it has to be a damper controlling the 2nd level..is the upper floor stat exactly like the main floor one?

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