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Old 09-16-2012, 11:32 PM  
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If you have a 110v at the furnace then you have 110v into transformer, which is called the primary, test the secondary side of transformer (24v) by followingthe leads from transformer going to the low voltage connections usually "R" & "C" or "X" thats the 24v connections. Depending on well who has worked on your furnace and the manufacturer there maybe be a fuse once the 24v leaves the transformer going to the low voltage/thermostat connections may be a inline car fuse or colored fuse. If you have 24v there than you will at stat. On a call for cooling your stat will send 24v to the AC unit normally the yellow wire or "y" connection. Your 2 low voltage wires at AC unit are the 24v, so check the voltage there. Then it can go thru safety switches, circuit board then the contactor so follow it. Theres also manual resets at the AC unit to high and low pressure you may try resetting them. Can go on and on but its a start to save u a buck. Make sure your meter is on AC volts and not DC volts too. Good Luck


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Old 09-17-2012, 06:08 PM  
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Originally Posted by randytrue View Post
OK, I'm getting 13V AC at the transformer output.
Can we assume the transformer is bad?

A partial short should be pretty difficult to trace down without cutting and jumpering some connections on your controller board.

Taking 40 VA as a generic rating for your transformer, the secondary current should be 40/24 = 1.7A or less. Check it if you can.
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