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Old 06-07-2010, 01:51 PM   #1
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Contactor Replacement problem


My a/c for awhile was blowing only hot air so I called out the local HVAC guy and he did an assessment on my system. Turns out the contactor and capacitor were bad and he gave me the part specifications I'd need.

He informed me that I should unplug my gas furnace before I did the job to avoid a nasty shock and so I did. I replaced the contactor and capacitor, but when I plugged my gas furnace back in it does not come on.

I removed the doors to check the lights and none of them come on.

Here are pictures of my current contactor/capacitor setup.









I wired it the same as my old contactor with the exception of the yellow and brown wires on the sides. My old contactor had the brown wire on the top portion and the yellow on the bottom. My new contactor seems to place them side by side.
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Old 06-07-2010, 03:08 PM   #2
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Contactor Replacement problem


Did the furnace fan come on?
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Old 06-07-2010, 03:20 PM   #3
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Contactor Replacement problem


No, the furnace fan is not coming on at all and the circuit board lights are not coming on either even after replacing the 2A Slow Blow fuse.
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Old 06-07-2010, 03:25 PM   #4
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Contactor Replacement problem


Was the fuse actually blown?

If so, make sure no strands of the low voltage wires that connect to the contacter are touching each other.

Turn your thermostat to off, before changing the fuse again, if its blown again. Then turn fan to on, and see if it works. If it does. Then switch it to cooling, and set it low enough to run. Might take 5 minutes for the outdoor unit to start. Your thermostat may have a delay built into it.
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Old 06-07-2010, 03:37 PM   #5
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Contactor Replacement problem


Does the wiring on the contactor look right? I matched it up to the old one, but it's the first time I've ever done it.

Yes, the fuse was blown. I had it checked at Radio Shack when I went to get a new one. I also picked up a multi-meter to check my wall voltage. It's reading steady at 120.8v
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Old 06-07-2010, 03:44 PM   #6
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Contactor Replacement problem


The low voltage looks right.

Hard to tell for sure on the contactor. Since I can't see what wires you have under the black and white.

As i look at it. It almost seems your missing a wire from the contactor to the capacitor.
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Old 06-07-2010, 03:45 PM   #7
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Contactor Replacement problem


Turn the power OFF.

You should only have 24 to 30 volts at the thermostat.

Sounds like you have a low voltage wire touching a line voltage terminal.
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Old 06-07-2010, 03:50 PM   #8
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Contactor Replacement problem


I have 120.8v coming out of the wall socket that my gad furnace connects to. The thermostat is not currently getting any power.
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Old 06-07-2010, 03:52 PM   #9
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Contactor Replacement problem


OK. You had me worried there.

You need to use that meter. And check the low voltage wires for shorts to ground, or to other wires.
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Old 06-07-2010, 03:52 PM   #10
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Contactor Replacement problem


Quote:
Originally Posted by beenthere View Post
The low voltage looks right.

Hard to tell for sure on the contactor. Since I can't see what wires you have under the black and white.

As i look at it. It almost seems your missing a wire from the contactor to the capacitor.

On my old contactor/capacitor I only had three wires connected to my capacitor and only one of them connected to the contactor.

Under the black and white wires are a red wire that goes down into the unit and the wire that connects to the capacitor.

Quote:
Originally Posted by beenthere View Post
OK. You had me worried there.

You need to use that meter. And check the low voltage wires for shorts to ground, or to other wires.

The voltage outside looks good, but the big thing I'm trying to figure out is why my gas furnace/fan isn't working now.

I turned the power to the outside unit off and then went inside and unplugged the gas furnace as directed by the HVAC tech that came out.

When I was done wiring the contactor/capacitor I went inside and plugged the furnace back in and then went outside and turned the power on the outside unit to on.

Ever since I unplugged the furnace it hasn't come back on.

Is it possible that my transformer blew? If so how do I check and would that cause my furnace circuit board to not light up?
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Old 06-07-2010, 04:13 PM   #11
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Contactor Replacement problem


Yes, your transformer may have blown also.

BUT. You NEED to find what caused it to blow. It wasn't from unplugging the furnace, and then plugging it back in.

You NEED to check for shorts first. And fix that. then if the transformer is blown, replace it, and the fuse if it blew again also.
Why install a new transformer without finding the cause. And burn out a new transformer also.
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Old 06-07-2010, 04:14 PM   #12
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Contactor Replacement problem


That would cause the board not to light up.

See if you have 24 volts coming to the fuse. If so, trans is good. If not, trans is burned out.
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Old 06-07-2010, 04:47 PM   #13
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Contactor Replacement problem


I just checked the voltage coming from the transformer to the fuse.

0.1v so it looks like I'm going to be buying a new transformer.

Here is the current one.



Should I replace it with the same or is there something better I should look into?
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Old 06-07-2010, 04:50 PM   #14
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Contactor Replacement problem


Can't tell for sure but it looks like the contactor has low voltage terminals on each side and you have both hooked to the same side. Are those terminals on the contactor right next to the capacitor?
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Old 06-07-2010, 05:09 PM   #15
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Contactor Replacement problem


The low voltage ones are the ones that connect to the coil right? If so I moved one to one side and one to the other shortly after taking those pictures. Also, yes it's near the capacitor.
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