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Question DetailsAsked on 9/15/2017

What is this noise in my walls?

I had my indoor AC unit fixed the beginning of this summer. Within the last week, it wasn't kicking on. I turned off my thermostat, turned off my breaker, turned the actual unit off, then turned everything back on. That seemed to work and my air is moving again. But I've heard some noise within my walls that would connect my indoor unit to the outdoor unit. Its not a humming or buzzing noise, more so a rattle. Never lasts more than five seconds. Just wanting to make sure I didn't make a small problem worse!

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1 Answer


Sounds to me, barring this just being a coincidental rattling of tubing, like you either have a compressor vibration transmitting to tubing (making it vibrate - probably during initial startup or at shutdown).

Another alternative would be slugging (liquid returning to the compressor) or "boiling" in the lines where the compressor is pushing compressed liquid refrigerant out of the condensor coil (the outside fan and coil) but instead of staying liquid till it expands in the evaproator unit (the indoor mini fan/evaporator coil wall unit) it is evaporating in the tubing and causing mini explosions of bubbles in the liquid, causing a vibration - like boiling surfacing in a stew pot. This could mean your unit is low on gas (even though it is still cooling), which would eventually cause compressor damage at is loses more pressure because in almost all household units the lubricating oil moves around with gas.

I would have it looked at - could be the repair at start of summer did not do the job - or fixed one leak of a couple, or something is now wrong - and you may need another repair.

Turning it and the power off and then restarting could also mean the compressor was slugging (trying to start with liquid for refrigerant in it instead of gas, which causes it to stall out and can also break it) or that it was overheating because of low refrigerant or other problem so the thermal protection breaker kicked it off, and it restarted because it cooled enough before you powered it back up.

Another possibility - the starting capacitor may be getting old and weak so the motor that drives the compressor is starting too slowly and hard and the resulting sustained high current draw tripped out the breaker (circuit breaker or thermal protection built-in breaker)

Either way, sorry to say it but time to call a Heating and A/C (your Search the List category for this service) tech to come diagnose the situation - I would give about 3:1 odds you are significantly low on refrigerant.

BTW - you can find a LOT of previous questions with answers on the typical repair costs, the repair versus replace decision process, and the economics of repairing an older or R-22 (Freon) unit versus putting in a new one. Look in the Home > HVAC link under Browse Projects, at lower left.

Answered 3 years ago by LCD

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