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Old 06-18-2011, 01:15 PM   #1
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Fuse blown in airhandler


I have a York heat pump and air handler. My sons called yesterday to say that AC isn't working. Got home this morning from work. After checking several items, found blown 5A fuse on air handler board. I replaced fuse, turned on fan and all worked fine. Turned to 'cool' and when the signal was sent to condenser outside, the fuse immediately blew. Searched for obvious shorts to the condenser outside and found none.

Could it have something to due with the contacter on the condenser and how would I rule this out before making another arbitrary run to town to buy the wrong part?

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Old 06-18-2011, 02:09 PM   #2
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Fuse blown in airhandler


There is a short, either a knick in a wire or two or possibly inside of the condenser the low voltage wires have come loose (the wire nut(s) fell off?) and are touching the cabinet.

You will continue to blow fuses until you find the problem.

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Old 06-18-2011, 02:10 PM   #3
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Fuse blown in airhandler


-Set to heat and see if it gonna blow the fuse.
-Isolate the thermostat.
-Check for shorts from furnace to thermostat wires.
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Old 06-18-2011, 02:31 PM   #4
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Fuse blown in airhandler


Quote:
Originally Posted by JJboy View Post
-Set to heat and see if it gonna blow the fuse.
This is excellent advice.
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Old 06-19-2011, 08:19 AM   #5
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Fuse blown in airhandler


remove the low voltage out at the condenser refuse the board and call for cooling..fuse holds then the problem is in the condenser contactor coil pressure control shorted doing this test will verify run out to the condenser from the stat down thru the AHU to outside....contactor coil for the compressor is a major draw on the TR and that fuse.....
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Old 06-19-2011, 11:04 AM   #6
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Fuse blown in airhandler


Thanks, Biggles.

This is actually what I did. I was convinced in the beginning that I had a short in the low v wire and climbed in the tight a** attic and examined. Not a knick found. So, I d/c from condenser, and when the unit 'called for cooling' no blown fuse. I wasted another fuse when I hooked it back up and tried again. When it 'called for cooling' it blew. Replaced contacter/coil in condenser and are now enjoying wonderfully cool, low humidity air in the Florida summer. Thanks for your advise, albeit after I stumbled on the solution naively on my own.
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Old 06-19-2011, 04:08 PM   #7
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Fuse blown in airhandler


contactor coils have a certain resistance in fact any coil no matter what it is controlling 120V 240V or even 480V it stll has to pull in the contactor and that is part of that VA you see on the TR rating.if the coil gets worn or shorts out right back to the fuse as it should.so next time yor at a neighborhood BBQ and some guy is saying how his fuse is blowing when he goes to cool calll.you kick in and say change the contactor.if you have access to an OHM meter check the old one vs the new 24v disconnected and you'll see a resistance difference....hvac service its not brain surgery believe me after 30yrs in it..enjoy those BTUs banging... the biggest draws in VA on a residential unit are the soilid state in the air handler,the digital stat,the condenser contactor because of the run outside into it

Last edited by biggles; 06-19-2011 at 04:11 PM.
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Old 06-20-2011, 05:24 PM   #8
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Fuse blown in airhandler


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Originally Posted by biggles View Post
remove the low voltage out at the condenser refuse the board and call for cooling..fuse holds then the problem is in the condenser contactor coil pressure control shorted doing this test will verify run out to the condenser from the stat down thru the AHU to outside....contactor coil for the compressor is a major draw on the TR and that fuse.....
Great service advice, I was going to say the same thing before I read yours.

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