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.

1) with the fan running in wrong direction the compressor will overheat and shut down in overload

2) no, the wiring on the capacitor could not cause the fan to run backwards

Thank you for the answers. Do you have any idea what is causing the fan to run backward when the compressor kicks on?

Have never heard of this happening, normaly the fan and compressor kick on at the same time, and as you said the fan should pull air in through the sides and blow upward out of the unit. I would think the fan motor will need to be replaced,also when replaced a new ,smaller capacitor will need to be bought that is correct for the new motor,, this capictor will be for the fan motor only,(not to replace) the one the compressor is connected to

The cap was replaced already. This unit uses a dual run cap with the spec 45-5 MFD 370VAC. He put in a 45-5MFD 440VAC. I am certain the higher VAC capacity is OK, and the MFD matches the OEM spec.

maybe so,, but the new motor takes a different capacitor than what is already in the unit for the compressor,, new motor =new capacitor for the new motor only

A bad compressor, capacitor, grounded wire or herm and common reversed on a dual capacitor will react the same way. If the new capacitor was way under sized it would not run at all. If it was over sized it would run but over heat over time.

I basically agree with T-top. The cap being hooked up incorrectly or bad and/or motor problem is my first guesses.

Take many of the posts about ceiling fans here. The inability of the fan to reverse itself when it's rotating and then turned on is usually a sign of a bad cap.

When the compressor starts, it causes a dip in the AC voltage going to the unit. This may be enough to reverse the direction.

Check wiring of the cap first.

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Originally Posted by Mounty

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.

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Was the outdoor fan running without the compressor initially, then the compressor started and the fan rotation reversed? If so, and you are certain the unit is wired correctly, you may have a problem with the compressor windings. A megohm check and amperage check of the compressor will reveal any electrical problems. A shunted winding may be causing power to "reverse" flow through the capacitor.

Here is the video. Hope it gives you an idea. No clue what happened to the sound.

Pay attention to 0:27 is when the fan comes on by itself after I shut the AC off and turn it back on. At 0:43, the compressor kicks on, reversing the fan to blow incorrectly.

YouTube - Lennox Fan Motor on Outside AC Unit Reverses Itself

KC13, I agree with you. I inherited the unit when I bought the house. Now, since you are from Cincy, any reputable tech you can recommend?

Wow, never seen this before. Interested to know what you find. I would definatley have all wiring in outdoor unit checked from start to finish. If compressor and fan are not bad at this time, they soon will be if this keeps happening. Please keep us posted, and good luck.

I have seen a couple of trane units do this before. I ended up replacing the fan motor.

It sounds like the compressor is running from the look of the video. By chance do you have a universal motor on your A/C unit with a reversible rotation(Four wires at the butt end of the motor that hook together.)

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Originally Posted by Mounty

Here is the video. Hope it gives you an idea. No clue what happened to the sound.

Pay attention to 0:27 is when the fan comes on by itself after I shut the AC off and turn it back on. At 0:43, the compressor kicks on, reversing the fan to blow incorrectly.

YouTube - Lennox Fan Motor on Outside AC Unit Reverses Itself

KC13, I agree with you. I inherited the unit when I bought the house. Now, since you are from Cincy, any reputable tech you can recommend?

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You mean, besides myself? No. However, we could arrange something... private message?

Yeah, if you don't mind. I don't think we can send private message here, why don't you email me at [email protected] and we can go from there. Thanks.

Oops, forgot to quote. The above message is a response to:

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Originally Posted by KC13

You mean, besides myself? No. However, we could arrange something...private message?

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It's fixed with a replacement fan motor. The old motor is OEM and is single direction, meaning it should not have run in reverse. Comparing to the new universal motor, the old motor seems to run very "loose."

No wiring was changed and the new fan runs fine, so the old motor was probably about to fail. I actually still have the old motor, and have no clue what to do with it now. LOL.

Put an Amprobe on that unit and test for amp/current draw on startup. Test the fan and also the compressor separately then test the combination of the two. Report back the numbers. I wonder if the wires were put back on to the capacitor correctly. It looks like phase shifting from the video.

After the replacement, the AC is fine now. We have had temp into the 90s these past few days and it is good to have air!

The wires are OK. From what I gathered, there is a problem with the winding in the old fan due to age.

I experience the same problem. Different HVAC tech gave me run around.
One wanted to change my fan, other wanted me to clean my coil and damaged my inside unit, third wanted to change both inside and outside units.

Finally, thanks to you tube video link I found on this site and careful
Talking to different people, came down to know that my fan motor is OK, but small capacitor was bad. Cost me $11 and few hours of good experience.

Unit has large cylinder with three terminal, which is for compressor and since fan was replaced, there was a separate capacitor with 2 terminal.
I replaced both and now my unit is quite and working fine.