AC Start Up Problem

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  #1  
Old 09-20-09, 10:31 AM
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AC Start Up Problem

Yesterday I found that my AC was not cooling. Blower was working fine inside the house, but the outside unit was not running. I discovered that the circuit breaker for the outside unit had tripped. When the breaker was reset it would hum loudly, the outside AC unit would run for about 4 seconds then the breaker would trip again.

The unit is a Trane XE1000, about 11 years old (not a heat pump unit, just an AC unit). After cutting power to the unit, I opened it up to inspect the wiring and components. I found that a hard start kit had been installed before I owned the house. I do not know if it was installed to reduce dimming of lights, or as a preventative measure to extend the life of the compressor, or because of a problem with compressor start-up. While probing the hard start capacitor terminals to make sure it was discharged, I found that one of the terminals of the cap appears burnt, and that same terminal broke off while I was probing it. I have removed the hard start cap and found that it is shorted.

My thinking is that the cap shorted, leading to the burnt terminal and the tripping of the breaker. We have had a ton of rain the last week, and there was a small amount of water inside the electrical area which could have contributed to the failure.

My questions are:
1) Would there be any harm in attempting to run the AC now that I've removed the shorted hard-start cap? The normal run cap for the fan and compressor is still in place. The hard-start relay is still in place. It will take a day or two to get a replacement hard-start cap, and we'd like to have AC during that time as long as doing so isn't likely to harm anything else (most importantly, the compressor).

2) Are there other components which could have been damaged by the failure of the hard start cap?

3) The answers to the above questions would probably be more obvious if I had a schematic of this unit (or a similar one) and of the hard-start kit wiring. So far, I haven't found such a schematic. Anyone know where such schematics can be found?

Thanks.
 
  #2  
Old 09-20-09, 12:19 PM
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My question is, does the condenser fan run when the power is applied. If not I would say you need to change both caps. If it starts it will be ok to run without the start cap.
 
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Old 09-20-09, 12:32 PM
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A burnt terminal is a bad situation that must be eliminated from the circuit when the start system is reestablished.

If it is a TXV refrigerant metered system & a piston compressor it probably won't start without the start cap.

The condenser fan must run & the compressor must start & run.

If it does start & work okay, make sure it is off for at least 10 minutes before it cycles on again.
 
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Old 09-20-09, 12:50 PM
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If the breaker you refer to is in the disconnect at the unit, do this:

Leave the breaker off for now.
Go in the house and set the thermostat so cool. You can set it to 60* or so.
Go back out to the unit.

Reset the breaker but leave your hand onit........

If the compressor and fan start up without any undue noise or strain then leave the breaker on and order up that capacitor.

If it makes any loud humming, popping or anything and it doesn't trip the breaker...... go ahead and turn the breaker off yourself.

Hope this helps.
 
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Old 09-20-09, 03:21 PM
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Thanks for the replies. I've checked the run capacitor (dual cap for the fan and compressor) and it appears to be just fine. I still have not run the AC since removing the hard-start cap. I am now going to disconnect the hard-start relay and try to run the AC.

Skip4661, the condenser fan does run just fine before the circuit breaker trips.

HVAC Retired, thanks for the tip on waiting 10 minutes after shutdown... will definitely do that if I get it to work.

VetNutJim, the breaker which hums and buzzes and then trips is the one in the household circuit breaker panel. I haven't noticed any humming from the disconnect right by the AC outside unit.

Will post again a little later with the results of my attempt to run without the hard-start circuit....
 
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Old 09-20-09, 04:27 PM
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Cool

AC started up just fine without the hard-start circuit, and has been running for 30 minutes now. No hum from the circuit breaker. It almost seems like the outside unit is running quieter now, but that's probably just my imagination.

Nice to have cool air again, just in time for the Cowboys game

New hard start cap will arrive Wednesday. One of the ground wires didn't look too good (cracked insulation), so I'll replace that at the same time. Are these HVAC lug connectors just the standard hardware-store variety, or do they have some special ratings?

Thanks again for the tips and advice.
 
 

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