Transformer fuse keeps blowing

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  #1  
Old 06-13-08, 05:22 PM
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Angry Transformer fuse keeps blowing

It started about two weeks ago, my power in my condo went out (all power). Turned out the main breaker tripped. I reset that and then the AC would not come back on.

Turned out the transformer blew. I have a heat pump system with the condensing unit outside and air unit in the attic.

When the repair tech replaced the transformer, he put a 3-amp inline fuse on the low side. Two weeks later, I came home from work one day and no AC. I checked that fuse and sure enough it was blown.

I replaced the fuse, but still no AC. I put in a 20-amp like an idiot and after some on and off, the transformer went, power to the whole condo went also. I reset the main breaker and waited for a tech to arrive.

He replaced the transformer at no charge, put a 5-amp fuse in, after 3 fuses, it worked. He wanted to charge $68 to plug in a breaker instead of a fuse, but i figured that I could just go and buy one myself, so he just installed the 5-amp fuse. I was back in business. I was a bit nervous because i knew the problem was not solved. He did not offer a solution either.

Well, two days later came home from work and no AC. I had bought some 5-amp fuses this time and was ready. I put one in tonight and all is well, AC working.

The problem is that it could blow at any minute. I have no idea why the low side transformer fuse keeps blowing. I checked the wiring outside and all seems fine on the exterior of the unit. I have not closely checked the wiring upstairs yet inside the unit.

Any ideas what to look for? I am pretty handy and can fix anything, just need to know where to look and what to look for.

thanks in advance, mike
 
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  #2  
Old 06-13-08, 05:28 PM
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Join Date: Jun 2008
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westnlas

I would visually inspect the wires at the switching area of the unit. I think one of the thermostat wires might be bare and grounding out when the unit moves as its starting or running. Take a look at the contactor points too. Good luck with it.
 
  #3  
Old 06-13-08, 07:28 PM
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Join Date: Feb 2008
Location: Ft. Worth / Dallas Texas!
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Mike,
Nine times out of ten the problem is in the 24 volt control wires going to the outside unit. You have a heat pump so it is 5 or more wires going to the outside unit.

Usually it's a weedeater or dog that has gotten hold of the cable and torn off the protective outer jacket and exposing the inner wires.

After a long time exposed to the sun the UV light will break down the coating on the wires and they will eventually just be bare wires in spots and can wind up touching and shorting out.

If you don't see any exposed wires out there you can cut the main power to the outside unit and take the access cover off and look where the low voltage thermostat wiring comes into the unit and see if one of the wire-nut caps has come off and it is occasionally touching the metal on the unit and shorting.

It's possible a rat or something has chewed some wiring in the attic. (I've never seen this yet) ...or that the thermostat wiring at the air handler / furnace in the attic has rubbed bare somewhere where it goes into the unit. (haven't seen that either but...)

...anyway just a few more ideas. If all else fails go spend some money and buy a roll of 8 conductor thermostat wire and re-wire it. (assuming the probem isn't between the air handler and thermostat) Just don't be up in a hot attic without someone there to keep an eye on you! Over heating is VERY easy and tends to sneak up on you!
 
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