Furnace Troubleshooting

willie52

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Jan 25, 2008
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Check the install instructions closely on your new thermostat, some of the newer ones require a jumper wire, if you wired it the same as your old one that could be an issue.
 

AUDub

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Give me ambiguity or give me something else.
Check the install instructions closely on your new thermostat, some of the newer ones require a jumper wire, if you wired it the same as your old one that could be an issue.
This is what I'm thinking too. In every smart thermostat I've ever purchased, there was a jumper factory preinstalled between RH and RC. Removing that jumper when it's required can result in the thermostat being unable to send heating and/or cooling calls.

Also, if you didn't note it while removing your old thermostat, do not trust the wiring colors. There's no guarantee they correspond to what they're supposed to (green - fan, yellow - AC, white - heat, R(ed)H and/or R(ed)C - hot wire for heating and cooling calls respectively, maybe blue or black - common) . I would recommend going to the furnace, removing the service panel and getting a look at the transformer and board the wires are connected to, making sure they correspond with what your thermostat requires. Label them if not already done so, too. Your new thermostat should have come with flag labels.
 
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AUDub

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Also, just a recommendation, if it’s a smart thermostat, like a Nest, you’re probably going to want to run a C wire if there’s not one run already, lest you have to replace batteries all the time. Hopefully, your thermostat cable either already had one run or has an unused wire you can utilize should it be necessary.

I’m not sure how comfortable you are working with electricity, but it’s not too tough to do. If you need a walkthrough or any sort of assistance, I will be glad to help.
 

TideMom2Boys

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We had to correct some things when we installed our Nest thermostats (two different units). It wasn't working when we first installed it, finally had to call and they walked us through it to correct the wires.
 

AUDub

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Give me ambiguity or give me something else.
We had to correct some things when we installed our Nest thermostats (two different units). It wasn't working when we first installed it, finally had to call and they walked us through it to correct the wires.
I had to run new 18/5 thermostat cable on one of mine, and meter out the cables on the other (the aforementioned expected color set was ignored by the original installer). Pretty straightforward operation, except the upstairs air handler did not have a dedicated C wire connection, so I ended up wiring it directly on to the ground screw of the secondary side of the transformer. Hasn't given me a bit of trouble.
 
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