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Old 07-23-2010, 04:42 PM   #1
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Low voltage help


Hello everyone,

I am having a problem with the 24v side of my outdoor unit. I went ahead and changed contactor's, but the problem persists. essentially, the unit will not turn on, as the contactor doesn't engage. The unit will work by manually engaging the contacts. The wires leading to the 24v side each have at least 24v, but I can't get a reading across the contactor (diagonnaly on the 24v side). When I take the thermostat out of the loop (y to r) it is the same. I have checked the voltages everywhere I can think of and they are all where they need to be. It seems that I have some phantom voltage somewhere, but I can't figure out how to track it down. I appreciate the help!

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Old 07-23-2010, 05:50 PM   #2
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Low voltage help


If you don't have 24 volts from one wire to the next outside. You don;'t have a completed circuit.

See if you have 24 volts from Y to C at the indoor unit.

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Old 07-23-2010, 06:45 PM   #3
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Low voltage help


To expand on what beenthere wrote.... Since you have 24 volts at each of the two wires it's safe to assume you are checking each to ground and not one to the other. Look for a broken wire hooked to the C terminal in the furnace.
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Old 07-24-2010, 08:24 AM   #4
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I have 24v on every y-c connection...but...when I tested the connection outside (some previous owner had to replace something with it obviously and just connected another wire harness to the existing one instead of running a whole new one) I heard this clicking from inside the unit. I decided to cut the power and undo the common connection outside and replace the wire (temporarily). When I tested it again, it was again fine. As the connection was considerably more loose, though, the clicking sped up considerably. I wiggled that wire and finally removed it and the click stopped. I took a picture of the thing that was clicking. I appreciate the help again!
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Old 07-24-2010, 08:35 AM   #5
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Low voltage help


The clicking, was the reversing valve. It clicks everytime it gets power, and then looses power.

Look for a low or high pressure switch to be open(check them by ohming them out).
Also, look for a reset button on them. Some high pressure switches are manual reset. They are installed so that you know you have a problem.
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Old 07-24-2010, 09:13 AM   #6
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Please forgive my ignorance. I looked online for pictures and found nothing that looked like anything I have. The unit only has one other connection to the copper lines and it just has wires hanging with wire nuts terminating them and electric tape wrapped neatly around. It looks like a thimble with two wires coming out (it's green if that helps). There is one other section that is wrapped in foam with no wires going to it. Sorry for not knowing alot. I really do appreciate the help though.
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Old 07-24-2010, 09:35 AM   #7
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not mentioned...your 24Volts control power for the contactor and that 3-way valve is supplied from the furnace not the condenser...put the wiring back as found call the AC in with fan in ON and recheck voltage at the contactor first if you don't read 24V with leads on each side of the coil a safty is opened or your not getting it from the stat...then check the 3-way the brands differ on heat mode/cool mode put up condenser brand and model..no power at the 3-way could be cooling mode...but get that 24v at the contactor first..
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Old 07-24-2010, 09:46 AM   #8
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Green thing?

Sounds like a pressure switch.

Post pic if you can.
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Old 07-24-2010, 10:47 AM   #9
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sorry for the ambiguity about the green thing.

I jumped the common and yellow to the contactor and it works on command, so it seems as if the issue is with the control board on the outside unit. I just need to figure out the reversing valve (whether to jump that to the yellow as well) to be able to have some cooling until a board gets in.
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Old 07-24-2010, 03:30 PM   #10
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Don't jump the reversing valve out.

The problem is probably not the defrost board. But a safety, causing the defrost board to keep from energizing the contactor.

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