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Old 06-23-2010, 06:41 PM   #1
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New control unit, but AC still not working


After a nasty storm over the weekend, our AC would no longer kick on and neither would the blower. I bought a new White Rodgers 50A55-843 control unit and installed it today. All went well except one ugly part. I accidentally connected the Line-H to the EAC-H terminal. The blower started running right away when I flipped the power switch on the side of the furnace. When I saw that the AC compressor wasn't running, I turned things off and rechecked, then found my mistake and switched the power line coming from the cover safety switch back to the Line-H terminal.
In this position I am not getting any blower and no AC.

I checked the 24 volt transformer and the control board is not supplying power to it. Did I blow my new $100 control unit by switching up the wires? I checked the fuse as well by the way and it is ok. I don't have any status light flashing errors either.

The house is 85 degrees so until I get it figured out, I ran a separate 24 volt AC transformer to the AC contactor to get the AC unit running, and I switched the hot line back to EAC to run the blower.

Any ideas?
Thanks,
Eric (hot and sweaty in Michigan..)

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Old 06-23-2010, 06:51 PM   #2
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New control unit, but AC still not working


You may have damaged the board. The EAC terminal gets energized when the board energizes the fan for heating or cooling. You backfed voltage to a relay which was not supposed to happen and after that damage occured.

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Old 06-23-2010, 07:51 PM   #3
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New control unit, but AC still not working


Guess you never checked to see if the thermostat was sending 24 volts to the Y and G terminal of the board.
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