AC not working. Blown transformer in furnace.

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Old 08-08-15, 02:06 PM
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AC not working. Blown transformer in furnace.

My AC stopped working. The 24 V transformer was blown on the supply side - the 24V side has a 5A fuse that was fine. I replaced the transformer and everything worked fine for a few days but then the transformer blew again, again on the supply side. Any advice on what to try next?
 
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Old 08-08-15, 02:42 PM
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Verify the correct voltage to the transformer, that it is correctly wired, that the furnace is properly grounded and that the breaker panel is properly connected to the steak in the ground.

I had a loose connection to the grounding steak outside damage transformers throughout the house.

The main breaker would need to be shut off before a loose connection to the ground steak could be addressed ( if it is present).
 
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Old 08-08-15, 02:44 PM
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You have a short on the high voltage wires. Might be rubbing on metal some where.
 
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Old 08-08-15, 03:46 PM
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The input voltage looked good and ground connection seemed ok. Any other ideas?
 
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Old 08-08-15, 04:33 PM
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Wouldn't a short on the high voltage wires just trip the breaker rather than burn out the transformer?
 
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Old 08-08-15, 04:36 PM
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My bad. yes you are right. What voltage did you get?
 
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Old 08-08-15, 05:29 PM
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121V. So the line voltage seems good.
 
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Old 08-08-15, 05:58 PM
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Are you using a multi voltage transformer?
 
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Old 08-08-15, 06:16 PM
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No. Just a simple 120v to 24v step down transformer.

If the capacitor on the fan motor is bad, could the back emf fry the transformer?
 
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Old 08-08-15, 07:06 PM
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I don't know what emf is ???
 
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Old 08-09-15, 04:29 AM
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EMF is "electromotive force", and the answer is no. The 24VAC from the transformer is the low voltage control signal. It operates relays which switch the 120/240VAC for the motors. It's possible that you have a bad contactor. If the contactor has an internal short on the coil winding, it would pull more current than normal. However, you would expect that the fuse would blow rather than blow the transformer. The only thing I can suggest is to replace the 5A fuse with a 3A one. 3A fuses are what is typically used, and will offer more protection to the transformer.
 
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Old 08-09-15, 04:51 AM
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Was it the original transformer that burned out the first time? What is the VA rating on the transformer you used?any prints with that unit that calls out the correct size fuse,it could have been oversized at some point.

Geo
 
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