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Old 05-05-2010, 06:09 AM   #1
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resi A/C with no cooling


The air handler is running, the outside compressor fan is not, and no circuit breaker looks to be tripped.

If there is one test that most techs would run first, what would it be?

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Old 05-05-2010, 12:21 PM   #2
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resi A/C with no cooling


Check for a blown low voltage fuse, push the contactor in manually to see if the unit runs and there is high voltage to it.

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Old 05-05-2010, 12:24 PM   #3
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resi A/C with no cooling


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Check for a blown low voltage fuse,
Located on the control board in the air handler? I've seen my tech do the contactor thing.

I should be back out to Reston in several weeks, so I'll ask the HO for the repair slip to see what it finally was.

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Old 05-05-2010, 12:36 PM   #4
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resi A/C with no cooling


Fuses can be on control boards, inline with 24 volt wiring from the transformer, mounted on an electrical box inside the furnace or air handler etc. Rodents love to chew 24 wiring to condensors and the fan can be running w/o a blown fuse if it is hardwired for continuous operation. Pressing the contactor narrows the problem down to high or low voltage quickly and requires very little tools. NOT recommended for DIYers as if there is a short in the compressor etc BAD things can happen. Experienced techs know what to do to SAFELY take shortcuts.
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Old 05-05-2010, 12:38 PM   #5
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resi A/C with no cooling


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Fuses can be on control boards, inline with 24 volt wiring from the transformer, mounted on an electrical box inside the furnace or air handler etc. Rodents love to chew 24 wiring to condensors and the fan can be running w/o a blown fuse if it is hardwired for continuous operation. Pressing the contactor narrows the problem down to high or low voltage quickly and requires very little tools. NOT recommended for DIYers as if there is a short in the compressor etc BAD things can happen. Experienced techs know what to do to SAFELY take shortcuts.
If the compressor is shorted the breaker will trip?
In any case if I ever do this contactor armature trick I'll use a long push stick.
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Old 05-05-2010, 12:42 PM   #6
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resi A/C with no cooling


Not if the compressor is in the process of dying on the spot. I had one do just that. One winding shorted to the casing and the compressor ran, overamped and blew the guts out of the fusite electrical plug, blew out the freon and started a fire with poisonous phosgene gas before it drew 30 amps and tripped the breaker. If a tech EVER sees a condensor fan running backwards or unusually slow DO NOT touch the condensor as the compressor could be shorting and you will be the conductor to ground and DIE.
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Old 05-05-2010, 03:57 PM   #7
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LOL...

I shouldn't laugh. But when the fusite blows, it can be funny watching a newbie jump out of his skin.

Sad thing is. Not all that many years ago. 2 techs were killed when it blew, and the oil came out and ignited as it was traveling toward them. And burned them to a crisp.
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Old 05-05-2010, 04:36 PM   #8
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OK, Fusite. . .

"A Fusite.RTM. plug, for example, is a hermeticallysealed connection block used in conjunction with can-type closures. It is adapted to be welded to the compressor's shell to allow the stator leads inside the shell to be connected to the power leads outside the shell."
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Old 05-05-2010, 04:37 PM   #9
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Beenthere,
WOW.
Thats awful!!
I had an OLD OLD Fedders with the obsolete rotary compressor blow one and spray oil all over an asbestos shingle wall. Damn, I could not wipe that stuff off and it was acidic. Not sure how I got away with that one but the customer abandoned the unit and never complained. An experienced tech knows where to not keep his face when working on units, must come from the old flame rollout/delayed ignition stuff we deal with.

The relief valve popping will give a newbie the scare of a life also. I learned everything the hard way.
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Old 05-05-2010, 05:17 PM   #10
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resi A/C with no cooling


First test on a non running condensing unit is always is there high voltage present. If so the second test is check for low voltage. Eliminates big blocks of potential problems out of the way so you can quickly narrow down to the real issue.


Had one Friday that could have been a widow maker. Condesor fan motor had been running slow since October with no call for cool. The HO forgot about it untill doing some spring yard work. I scratched my head for a second, pulled the disconnect, took the cover off and checked for shorts. Compressor was shorted to ground so one leg went through the solid bussed side of the contactor, through the motor and capacitor straight to the grounded compressor.
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Old 05-05-2010, 05:41 PM   #11
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EXACTLY what happened to me except I was standing right beside it with my customer when it blew. Fortunately not in front of it. The old double pole contactors were safer.
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Old 05-06-2010, 06:35 AM   #12
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Quote:
Originally Posted by yuri View Post
Beenthere,
WOW.
Thats awful!!
I had an OLD OLD Fedders with the obsolete rotary compressor blow one and spray oil all over an asbestos shingle wall. Damn, I could not wipe that stuff off and it was acidic. Not sure how I got away with that one but the customer abandoned the unit and never complained. An experienced tech knows where to not keep his face when working on units, must come from the old flame rollout/delayed ignition stuff we deal with.

The relief valve popping will give a newbie the scare of a life also. I learned everything the hard way.
It gave me the scare of my life, cleaning a very large wall unit half in half out guess it wan't enough air for the condenser relief went off I almost died I was shaking for a while thinking that was the last resort before it could have been a bomb, thank GOD for the internal relief. That was at least 30 years ago and never happened again.
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Old 05-06-2010, 06:58 AM   #13
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I use to curse the companies that turn the compressor so that cockhead was faced away from the access panel. Because it was too hard to get to, in order to check the windings.

Until one blew. then I was understood why.

Had one blow on a 4 year old 10 SEER Ducane heat pump. that had 3 months left on its warranty. Had a new guy with me. His face turned white. There was more then just an oil stain after it blew.

I don't think that oil stain ever fades away.
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Old 05-06-2010, 03:35 PM   #14
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resi A/C with no cooling


ok guess ill add mine,was a newbie with a seasoned tech working on a 15 ton double compressor unit at a goodyear store dont remember all the details but i think he reset the breakers downstairs and wanted me to yell to him if it had restarted. it sounded weird and before i could yell anything it blew out at me combined with the lovely noise created by a dead ground and fireball, i ran backwards without looking and ttripped over the ledge of the open roof hatch lucky for me i actually fell over the hatch instead of thru it. The tech almost pissed himself laughing,I never saw the humor tho.... ken
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Old 05-06-2010, 03:48 PM   #15
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resi A/C with no cooling


That DEAD ground is a lovely sound though. Groaning and moaning. Now we need some "welders flash" stories.

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