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What’s That Noise From My Car’s AC?

It’s incredibly annoying, you’re driving down the highway and your car starts to squeal like something terrible is happening under the hood.  But for some reason, it only happens when your air conditioner is actually turned on.  With climate controls off or only the fan running, everything is quiet, but the second that compressor is turned on, your car sounds like something is dying inside.  The good news is that the problem is usually simple, but it can be difficult to identify.  If it only starts when the AC unit is running, then it’s likely a belt or a fan bearing.

Movers and Belts

We’re talking about the squealing noise your car makes when the compressor is turned on.  This can happen while idling or driving (low or high speeds too).  Especially with older cars, this is an incredibly common noise and, so long as it doesn’t last for longer than a minute (give or take 15 seconds), you likely have no issue with your car.  If the noise persists for longer, it’s a good idea to take it into the shop or do a little hands-on work if you’re feeling confident.

As we’ve said before, the AC unit in your car is very similar to the forced air cooling in your home, just on a smaller scale.  If you drive an older car, you’ll find there’s only an ON option for the compressor.  Just as you wouldn’t run it all the time at home, you may find you get better mileage by keeping the compressor on when you need to cool the air, and just running the fan once the internal air is cold enough.  Once you start noticing a squealing noise during the compressor ON cycle, then it’s time to take a look at possible causes.

Fan Bearings: If you have a newer vehicle, the condenser fan (similar to the blower motor in your home’s AC unit) can wear out as the bearings age.  The bearings can begin to squeak and grind whenever the compressor is engaged.  This fan is designed to draw air across the condenser coils, which is why you only hear the noise when the AC unit begins to operate.  If you feel the problem lies with the blower fan bearings, then we highly advise seeking professional assistance in replacing the fan, as it’s more difficult than a belt replacement.

Aging Belts: Older AC units in your car are driven by air conditioner belts.  These belts are not always connected to the system (since they’re only needed when the compressor is running).  Once the compressor is engaged, the belt begins to spin.  If the belt is loose or slipping it can create a high-pitched squeal.  Belts that have been improperly tightened, are cracked, or simply too worn to grip correctly have a tendency to slip and cause this noise.  Best response is to replace the belt and give it a few weeks of operation.  Be careful about adding belt dressing.  Yes, it can quiet the noise from a serpentine or AC belt, but with newer belts that can cause the squeal to come back with a vengeance afterward.  If you use a belt dressing, you will need to reapply it regularly or else the belt will dry out.

If you’re hearing similar squealing or other strange noises from your HVAC unit this summer, the problems could be similar.  Many noises are due to the blower motor or obstructions in your ventilation system.  If you’re worried about a noise, don’t hesitate to call us!

Metro Plumbing, Heating, and Air Conditioning is the service company you want!  Call us today at (423) 616-1025!

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