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Question DetailsAsked on 7/22/2015

My AC compressor at the rear side of my townhouse is making a strange noise intermittently. Is it normal?

My AC compressor at the rear side of my townhouse is making a strange noise intermittently. Is it normal? Will it require some diagnostic services by an HVAC expert?

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2 Answers


Best to have it checked, along with a good annual maintenance on the system that includes cleaning the indoor and outdoor coil.

Here's a vidoe about what to look for in an annual maintenance/check-up;


Answered 5 years ago by BayAreaAC


If it is making a sound it did not before, turn it off and check for debris like a twig caught in the fan unit, drive belt (if it has one) frayed or loose. Other than removing any debris that the fan or pulleys are hitting there is not anything you can do - turn it off and leave it off till checked out to prevent further damage.

If you are new to the house so don't know what the unit sounds like, generally it may give a bit of a thunk or whirr on startup, then of course a whirring motor noise from cooling fan and compressor, and on shutdown commonly a hissing in the piping valves near the compressor. Any sort of screeching, whining, thumping, scratching, or hissing sound when running would be unusual and probably indicative of a problem. You could also (if you have met neighbors) ask the nearest ones if they recognize the sounds your unit is making as normal or unusual - but I would not put too much weight to that assessment. Also - if new to the house - if you do not know when it was lasst serviced, a servicing at the same time as the diagnosis would probably be in order - typically about $70-125 charge for that depending on time of year - in higher end right now in most parts of the country.

Unusual noise is commonly due to loss of refrigerant (which almost always also carries the lubricating oil for the compressor, a bent fan blade due to impact by something, a malfunctioning temperature and pressure valve, or occasionally a problem with the compressor or condensor fan motor.

Diagnosis probably about $50-100, then repair can be as little as $10-20 additional for minor part like a drive belt on up, depending on what the problem is.

Be aware (read some of the discussions in the Home > HVAC link in Browse Projects, at lower left) that if you have an older R-22 (Freon) gas unit, if they say you need major repairs you may be better off replacing the unit with a new one using R-410a, because Freon is being phased out so recharging your unit will be tougher and more expensive as the years go by. Also, if an older unit, newer ones are more efficient so rather than sinking money into a 10+ year old unit, you might be better off with a new unit with higher efficiency and a new warranty.

Answered 5 years ago by LCD

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