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Old 05-23-2009, 05:10 PM   #1
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Fan on Outside Unit reverses direction when compressor kicks on


I have a Lennox 12ACB30-4P Value Series manufactured in 1996. It came with the house I bought 3 years ago. The unit never gave me any problem until 1 week ago when it would not cool. The fan would run, but the compressor would not kick in. There was a buzz every 20 seconds or so.

A tech was called based on the sticker on the unit (original installing company, but the residential service was sold, the new company still have service records.)

First tech looked and the wire was disconnected from the capacitor. He replaced it and cleaned it. All was well for 3 days, and there was no cool air again. The buzz returned in an interval of about 1 minute.

Called the company back and argued about cost of having to fix the same problem twice. Second tech came out the same day. The wire was disconnected again. This time, he replaced the capacitor and said the fan is running is reverse and would cost $400 to replace.

I thought I was crazy as I remembered the fan running in the correct direction (counter clockwise with air blowing out the top) before the capacitor was replaced. He left when the air is cool again (60F at the vent). I then turned off the unit by kicking the thermostat high. then waited several minutes.

When I started it again with the thermostat, the fan was running counter-clockwise with air blowing out the top. As soon as I heard the buzz and the compressor properly kicked in, the fan REVERSED itself to run in clockwise direction, with air blowing out the sides. I called the tech back, he said he has no clue and has to research. AFAIK, I do not think either tech has touched the fan itself.

Here are a couple questions:

1) Is it safe to run the AC in this condition? Would the fan motor and/or the compressor be damaged? I do not know if it was always running like this before the capacitor change.

2) Could the wiring on the capacitor be causing this? That is, could the second tech have wired the capacitor wrong?

Thank you. I appreciate any input.

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Last edited by Mounty; 05-23-2009 at 05:17 PM.
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Old 05-23-2009, 05:18 PM   #2
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Fan on Outside Unit reverses direction when compressor kicks on


No, its no safe for the unit to be running like that.
Could wipe out your compressor.

Fan motor could be bad. And have a low resistance short to ground.

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Old 05-23-2009, 07:49 PM   #3
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Fan on Outside Unit reverses direction when compressor kicks on


im with been rpl the mtr as at the very least it overheated badly from not starting due to the discoed cap. wire
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Old 05-23-2009, 08:06 PM   #4
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Fan on Outside Unit reverses direction when compressor kicks on


Yep. Had one just the other day.

Bad cap .

I have also seen this happen is low supply voltage situations that partially
burnt contacts on the contactor. Not only was the fan running in reverse, so was the scroll comp.

Ain't seen that one since.
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Old 05-23-2009, 08:32 PM   #5
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Fan on Outside Unit reverses direction when compressor kicks on


Thank you for all the answers so far. I have checked the wiring with the schematics on the cover. It looks like the wiring is correct. The capacitor was replaced today with a Dual Run 45-5 MFD - 440VAC (3 poles). It does not leak and is not swollen. He even left me the box that the cap came in.

As far as the contactor, I don't see any burn anywhere.

kennzz05, so the fan motor is probably shot due to overheating when the compressor wasn't kicking in? It does not make noise (bearing) and spins freely. The only thing is it goes both direction (Not randomly, counter-clockwise when compressor is off, clockwise when compressor is on.) There is cold air if I dare to turn it on.
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Old 05-24-2009, 01:09 AM   #6
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Fan on Outside Unit reverses direction when compressor kicks on


All, the tech out in a 45-5 MFD - 440VAC dual run capacitor. The manufacturer calls for a 45-5 MFD - 370VAC dual run capacitor. Could the difference in the VAC value be the cause? Thanks.
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Old 05-24-2009, 01:28 AM   #7
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Fan on Outside Unit reverses direction when compressor kicks on


An A/C fan motor reversing direction on a single phase power Supply? Sounds strange. From an Electrician's point of view (not an A/C tech.) Don't tell me that you have Three Phase power in a residential setting!!!
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Old 05-24-2009, 01:43 AM   #8
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Fan on Outside Unit reverses direction when compressor kicks on


spark plug, it is single phrase, per the service manual. Yes it is weird, especially when I see how the fan did the reversal. I need to youtube this one for you all. Everyone is thinking I have three heads or something.
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Old 05-24-2009, 06:30 AM   #9
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Fan on Outside Unit reverses direction when compressor kicks on


No. The voltge rating of the cap has no bearing whcih direction the fan motor rotates.I put a lot of 440 volt rated cap on both compressors, and fan motors that are rated for use with 370 volt caps.Its common. And saves stock room in the truck.
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Old 05-24-2009, 09:18 AM   #10
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Fan on Outside Unit reverses direction when compressor kicks on


You can upsize the mfd rating but never downsize it. Ie; 440 is OK for 370 but 370 is not OK for 440. The motor should be replaced as the shellac on the windings is overheated and will fail soon. At 13 yrs old it has seen a lot of use already.
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Old 05-24-2009, 09:20 AM   #11
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Fan on Outside Unit reverses direction when compressor kicks on


Yuri.I think you mean Voltage, not MFD.
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Old 05-24-2009, 09:56 AM   #12
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Fan on Outside Unit reverses direction when compressor kicks on


True. The old kapusta a bit slow today. Going to do some research on split phase motors. The start winding determines the direction of rotation. If not energized cleanly/fast enough or strong enough the motor may run backwards if I remember my NATE stuff correctly.
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Old 05-24-2009, 10:01 AM   #13
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Fan on Outside Unit reverses direction when compressor kicks on


Your right. It will start in reverse at times if the cap is weak.But, a weak cap usually only effects rotation at start up, not after its already running.And a shorting start winding can also do the same thing.
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Old 05-24-2009, 10:03 AM   #14
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Fan on Outside Unit reverses direction when compressor kicks on


I've been following this thread and I'm fascinated that the motor could go in a different direction if the cap is bad.

Question for you guys - when replacing a capacitor on a HVAC unit - as long as the breakers are off - is there any charge in an HVAC capacitor? Just curious as I'm finding this info handy.

Thanks.
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Old 05-24-2009, 10:07 AM   #15
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Fan on Outside Unit reverses direction when compressor kicks on


yes, there is

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