Spilt AC Interior Unit Inoperative Quick Fix


Old 07-21-20, 03:17 PM
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Split AC Inoperative - Found Quick Fix

Mini Split AC when first powered on display showed correct temp for few seconds, then showed garbage for next few seconds and finally went dark. AC did not operate. Split is 8 year old Chinese 9000 BTU.

From inside wall unit removed printed circuit board. Found brown residue on case of round electrolytic 1000 mfd 20 VDC capacitor and nearby 1/8 watt resister. Another resistor also had brown debris.

There was also tiny thread, fraction size of human hair, bridging several items. Apparently some bug was fried when unit was powered up.

Cleaned off debris, powered on unit and now working great. Calling in repair or replacement would have cost lots of money.

Modern AC electronic circuit boards have many failure modes. I have long experience with electronic repair. Often problems can be found by careful, through visual inspection of board. Look for foreign debris, burned or darkened components, broken traces/wires, bad solder joints.

Hope this post may help others.


Last edited by doughess; 07-21-20 at 05:40 PM.
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Old 07-21-20, 05:39 PM
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You were lucky.

Many of those boards have a conformal coating on them..... and some don't.... to reduce that problem.
Old 07-21-20, 06:15 PM
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Conformal coating are not widely used on consumer grade printed circuit boards.

Tried to buy a can today and are not locally available. Will use a clear gloss spray instead. There are no hi temperature items or RF radio frequency on board so it should be OK.

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