Outdoor condenser shutting off while compressor is running. Replaced capacitor, fan motor, and defrost control board. Problem only happens when fan is plugged into defrost board. What could it be?

For some reason, our outdoor unit condenser fan will occasionally shut off while the compressor keeps running. When this happens it starts blowing hot air in the house, not to mention the danger of the compressor overheating. The fan will eventually cut back on, usually within 15 to 30 minutes.

I've had multiple HVAC guys out. The capacitor is fine. We first replaced the fan motor, and it still did it. After another guy came out, he unplugged the fan from the defrost control board so that it would run all the time. He said if it doesn't do it not plugged into the board, then it's the defrost board that's the problem.

Well, sure enough, the problem went away when the fan wasn't plugged into the board. The other day I ordered a replacement part and installed it, feeling sure this would fix it. Nope, same problem as soon as the fan was plugged back into the new board. I've double checked to make sure it's the right replacement board and everything seems to be correct.

I had the same HVAC guy come back out and look at it, and he was bewildered. He said he had no idea what was causing it, or why the fan would be shutting off. He said the system is an older one that doesn't use sensors but just uses a timer, so it wouldn't be a bad sensor or anything like that.

So it seems like for some reason the defrost is running and killing the fan when in cool mode, which it shouldn't be doing.

Does anyone have any clue what in the world we could do besides replacing the entire unit? Thanks for the help.

submitted by /u/lavabootswill
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