Help troubleshooting low voltage problem


Old 07-07-13, 10:54 AM
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Join Date: Jul 2013
Location: usa
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Help troubleshooting low voltage problem

Bought this house last year. It has a lennox gas furnace and an arcoaire condensing unit.

When we moved in, we had no heat. The control board in the furnace was replaced. The technician got the heat working, but told me that there was something wrong with the low voltage wiring. I didn't have the money to have him troubleshoot, but he showed me what a mess the wiring was. 18/4 from the board was spliced into a couple of pieces of 18/2, and there were 3 of those coming out of the hole at the thermostat. The wires for the AC were not even connected.

i left well enough alone all winter, but i had some free time this weekend, and it is really hot, so i thought i'd rewire it. it's really easily accessible.

Now I have 1 single piece of 18/5 (only using 4 of the wires) wired exactly like the diagram shows from the furnace control board to the thermostat.

i had hoped that fixing it would solve my problems, but i seemed to have created new ones. i don't have any low voltage at the thermostat. I went out to the condenser and pulled the low voltage wires off the contactor, and measured there, and got nothing.

so i went to the control board in the furnace, and measured at the screws there. No low voltage there, either.

If you have a second, could you maybe help me figure out what to check/try next?
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Old 07-07-13, 03:23 PM
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Join Date: Jul 2013
Location: usa
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never mind - found a blown fuse. AC is blowing cold!
Old 07-07-13, 03:31 PM
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Just as an aside here......always turn off the compressor and furnace/air handler when making wire changes. There is not always a protection fuse and if the wiring is shorted could damage the control board. Control boards start at 100.00 and go up much higher.

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