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Old 07-06-2013, 10:37 PM   #1
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Help w/ t-stat / low voltage wiring?


When i bought this house the t-stat wiring was a mess. It is easy to access so I decided to replace it.

I don't want to waste a lot of words on the problems, rather than figure out what was spliced where, i though i would just rewire it and be done with it.

I thought i had it all figured out, but i got myself confused when i took the t-stat off.

The board in the furnace has 5 screws; R, W, Y, G, C. So I ran 18/5.

The Thermostat has 5 screws; Rh, Rc, Y, W, G

The connection diagram shows 4 wires (R,W,Y,G) running to the t-stat. The condenser is shown wired to Y and C.

I think now that I did not need 18/5, and that I should only use 4 wires, jumping the Rc and Rh at the thermostat.

Does that seem right?

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Old 07-06-2013, 10:54 PM   #2
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Help w/ t-stat / low voltage wiring?


You have an extra wire for now. Don't cut it off, you will need it if you ever upgrade to a thermostat that needs a power supply. Just wind it around the others. The condenser has to have the "c" wire to one side of the contactor, and the yellow from the thermostat to the other.

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Old 07-06-2013, 11:11 PM   #3
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Help w/ t-stat / low voltage wiring?


You're welcome. I should have mentioned that the "c" and yellow wires go to the coil on the contactor.

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Old 07-07-2013, 01:13 PM   #4
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Help w/ t-stat / low voltage wiring?


well, that didn't seem to work. i don't think i have any low voltage anywhere. I took the thermostat off, and put a volt meter between red and every other color, and got nothing.

Then I went to the furnace and did the same thing at the control board, and still got no low voltage anywhere.

What should i check next?
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Old 07-07-2013, 01:50 PM   #5
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Help w/ t-stat / low voltage wiring?


Look for blown fuse. Or a bad transformer.
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Old 07-07-2013, 02:57 PM   #6
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Help w/ t-stat / low voltage wiring?


Thank you beenthere. You are right - there is a small 5a fuse in the path, and it is open. Off to the store now.

edited to add - WOOT! blowing cold air!!!! Thanks so much to both of you!!!

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Last edited by angelatc; 07-07-2013 at 05:55 PM.
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