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I'm installing a thermostat, but I don't appear to have a C wire. My old thermostat had R/RH,Y,G,and W. It's an AC system that was setup before I got here. The actual AC unit is a long way away and inaccessible because of how the community was built.

I never use my heater and when I measured the voltage, it was 24V (the same as C), so can I use that instead? I read that you can use the fan wire, but I turn my fan to 'ON' at night. I thought if I never use my heater, why not use that? Or am I missing something.

I also have a random blue wire bundled behind my wall, but it didn't power on my thermostat. It read 13V in my multimeter.

Image to my blower and the wires I see

Image to my blower and the wires I see

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    Is the heater unit/air handler accessible? Normally, the thermostat wires go to there first, not the A/C outdoor unit (condenser/compressor) – ThreePhaseEel Sep 6 '16 at 23:04
  • yes! after your comment, I went looking around my house and found where it was installed. I added an image I took of it to my post! Thank you! – CREW Sep 7 '16 at 0:56
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    What model is the air handler/heater? The fat blue wires look like they'd be coming from the 24VAC transformer, but I'd need to see a wiring diagram to be sure – ThreePhaseEel Sep 7 '16 at 2:31
  • It's a goodman on all ends. I attached a picture to my post above. I think its a ACNF24-0816, i have a multimeter, what should i connect the other end to – CREW Sep 7 '16 at 5:56
  • I looked into it a little more today and it looks like that blue wire I found tucked wasn't actually hooked to anything. When I read 13v earlier, I must have been reading the other wire I used (the red). So i can use that wire if needed, but is there a way to find the 24v source? What two wires would I use to test against each other. Looks like the big brown isnt hooked to anything, and there's the blue green and red big wires – CREW Sep 7 '16 at 19:45

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