York Furnace PS8C20N100UH11C Control Board

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Old 06-21-09, 11:21 AM
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York Furnace PS8C20N100UH11C Control Board

Can anyone tell me how to test control board.


I tied to use AC yesterday for first this year, and it did
not work after putting fuses back in box outside and turning breaker on. Thermostat cliked was all it did.

so I inspected furnace and found burned 3amp fuse and it imediatly blew again after replacing.

I checked wiring that goes two outside
condenser and looks good (no damage).

now when i replace the fuse it does nothing. nothing works
including heat or fan by itself.

the furnace/AC was new in march '07
 
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Old 06-22-09, 04:50 AM
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I removed control board and could not see any signs of overheating or shorts. I tested the 120/24 volt transformer
and it is not working.

Today I'm going to replace it, but I still dont know what caused it to short in the first place, since everything else worked fine before i attempted to use the AC.
 
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Old 06-22-09, 06:41 AM
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look for the R and C terminals and see if you have 24 volts there. Is it still blowing the 3amp fuse? id you use a spare fuse that was in the unit? Don't use an automotive fuse, it wil be the wrong voltage

update- replace the transformer, use one that is at least 40 va. Before you power back up, remove the wires that go to the outdoor unit [not the power wires, the control wires] and see if the fuse blowing stops.
 
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Old 06-22-09, 03:04 PM
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thanks dj,

i got new transformer today, and heat and fan are working again. the dealer took my old one and gave me a new one
and said its still under warranty, so no charge for parts.

other dealers told me electrical was not covered under warranty, and wanted to send a tech out.

when trying AC again after replacing transformer, it blew fuse. I disconnected wires going
to the relay/switch outside on AC unit and it did not blow fuse this time. AC works when I manually press the contacts on the relay, so tomorrow Im going back the the dealer and he said he will give me a new relay.

Hope my problem is fixed after that, its getting hot out.
 
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Old 06-23-09, 04:25 AM
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Be sure to scope out the wiring inside the unit as welll. We had a gentleman here a couple weeks ago where his heat pump kept burning transformers up. Turned out a wire inside the outdoor unit had been sitting on a hot pipe and when the insulation melted away there was a direct short to ground. If you unplug the 24v wires to the relay, does it still blow a fuse?
 
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Old 06-23-09, 04:39 AM
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No it did not blow fuse when wires were disconnected.
only when i send the 24V to the contactor/relay.

I removed the contactor last night and tried to test relay
by itself with another old 24V ac tranformer i had. I think the coil in the relay is dead.
 
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Old 06-23-09, 04:52 AM
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I've had morons, er..technicians, who couldn't even figure it out to do that. You da man.
 
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Old 06-24-09, 09:29 AM
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Replaced relay on AC unit and everything is working again.
 
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Old 06-24-09, 02:08 PM
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Great Thanks for the feedback.
 
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