Changing Thermostat - No Power To C Wire


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Old 09-13-18, 02:33 PM
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Changing Thermostat - No Power To C Wire

Hi all. I was swapping out my old thermostat with a new Honeywell Wifi thermostat. I took the following steps below.

1) Removed the plate of the old thermostat, and confirmed that the blue wire (C wire) has power running to it using a Fluke volt alert tool.
2) Turned off the power to the thermostat (fuse box).
3) Removed all the colored wires from the old thermostat.
4) Installed the colored wires into the new thermostat.
5) Flipped the fuse switch on again (at the fuse box).

At this point, I confirmed that the new thermostat would not turn on. I removed the new thermostat face plate to expose the wires again, and used my Fluke volt alert tool to again test the blue C wire. No power. I flipped the correct fuse switch off, then on again. No joy....still no power to the C wire.

Any ideas? As I was replacing the thermostat, I thought I heard the furnace (on a different fuse box switch that I left on) try to run and then turn off again, but not 100% sure.

I am ready to have an electrician friend come out to my home to take a look, but thought I would jump on here first to see if this is something simple I am missing.

Thanks!
 
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  #2  
Old 09-13-18, 03:49 PM
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Welcome to the forums.

Is this a heat pump system or furnace with split A/C ?
If you didn't turn power off at the air handler or furnace..... you probably blew a fuse.... or the transformer when the C wire touched another wire.

C is not power. R is 24v power. C is equivalent to the negative in a DC circuit.

You need to use a meter to confirm 24vAC between C and R.
 
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Old 09-13-18, 03:51 PM
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Thank you. This is a furnace with A/C, not heat pump.

I have an electrician friend coming tonight to take a look, and will report back.
 
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Old 04-29-19, 08:51 AM
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What did your electrician friend say about your setup? I am having a similar problem.
 
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Old 04-29-19, 09:06 AM
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Welcome to the forums.

Start a new thread describing your problem.
 
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Old 04-30-19, 10:34 AM
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PJmax was correct. There is a fuse I did not even know about in the furnace itself. I probably touched the wires when replacing the thermostat, and that blew the fuse in the furnace. It did not matter how many times I flipped the fuse on the main home circuit breaker box, the furnace still would not turn on for me.

I eventually replaced that fuse in the furnace itself, and everything worked perfectly. I have a Rheem Criterion II gas furnace, and the fuse was right inside the door I take off to replace/clean my furnace filters, on the left side.
 
 

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