Replacing Thermostat / Power Issue?


Old 07-19-14, 10:40 AM
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Replacing Thermostat / Power Issue?

Decided to final replace my extremely old 1970's thermostat with a new programable one. I turned the power off at the circuit breaker and turned off the larger circuit breaker next to the unit outside. The A/C doesn't turn on but when I turn the fan on from the auto position the fan comes on? Is this normal which means I'll need to turn the whole house power off or is it safe to move forward with the swap out?

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Old 07-19-14, 10:47 AM
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Thermostat power is supplied by the indoor unit.
If you have a gas furnace it is usually just a "light" switch by the furnace.
Old 07-19-14, 10:48 AM
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If the fan is still coming on, the air handler/furnace is still powered up. The thermostat gets power from a 24VAC transformer, which is usually located in/on the air handler/furnace. I'm guessing that there is another circuit breaker that controls the air handler/furnace (perhaps the circuit breaker panel is labeled incorrectly). You should make sure that the 24VAC going to the thermostat is turned off before proceeding with the thermostat swap.
Old 07-19-14, 12:05 PM
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Thanks guys for the quick reply.

I couldn't find the other breaker anywhere nor did I have a switch next to the unit itself so I just went ahead and shut the house off to be safe. Just like the package said... 15 minutes install time, easy!

New thermostat is working and all is good.
Old 07-19-14, 12:43 PM
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Add a service switch to a list of your jobs.

You can also open blower door to shut off power but a service switch is good to have.

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