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Automotive

What Is an AC Pulley?

By Lori Kilchermann
Updated Jan 27, 2024
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The AC pulley, or air conditioning pulley, is located on the front of the air conditioning compressor and drives the compressor with help from the engine's accessory drive system. Older versions of this pulley, found on vehicles prior to the mid 1980s, used a V-belt; since then, the system has used a multi-ribbed serpentine belt to drive the system. The AC pulley is attached to an electronic clutch, which allows the pulley to spin freely when the AC unit is not in use, but, once the compressor is activated by the AC switch, the clutch engages and the pulley drives the compressor.

There is rarely ever an issue with the AC pulley itself, however, the bearing that the pulley rides on typically requires occasional replacement. The electronic clutch system that works with this pulley can be heard engaging as a noticeable clicking sound when the air conditioning system is in use. A slight drop in engine speed is often found accompanying the clutch activation. An AC pulley bearing requiring replacement can often be indicated by a squealing sound coming from the AC compressor, as well as a noticeable wobble in the pulley itself as it spins with the vehicle's engine running.

A failed electronic clutch on a vehicle's AC compressor can lead to the freeze up of the AC pulley which, in turn, destroys the belt. This situation is dangerous due to the serpentine belt powering not only the AC unit, but the vehicle's charging and cooling systems as well. Typically, the pulley will freeze due to a malfunction in the electronic clutch or the failure of the pulley's bearing. Either of these conditions will be foreshadowed by a squealing or grinding noise emanating from the front of the AC compressor unit. This condition is commonly found only in vehicles that are driven with an inoperative AC system for long periods.

If a vehicle's air conditioning system is not working and will not be repaired, one remedy to avoid a frozen AC pulley from destroying the vehicle's belt system is to obtain a non-air conditioning-equipped fan belt. On a V-belt-equipped engine, it is often possible to simply remove the fan belts from the AC pulley. On this type of system, the air conditioner commonly uses a dedicated fan belt running off of another engine accessory to power the air compressor. This dedicated belt or belts can be removed, effectively disabling the air conditioning compressor with no further action required.

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Discussion Comments

By seag47 — On Dec 08, 2011

@OeKc05 – I had a similar experience with an old car. I had to drive it to and from work, because it was my only means of transportation. I always rolled down the windows for air, because I could not afford to have the air conditioner repaired.

One day on my way to work, smoke started emanating from the hood. I looked down at the gauges and saw that it was running hot. I pulled over quickly and called my boss.

He just happened to know a lot about cars, so he came out to take a look. He asked me if I had any plans to fix the air conditioning, and I told him that I could live without it. So, he simply removed the belt and disabled the compressor.

I didn't even have to pay for a repairman or towing! I was so glad he knew this trick, because I was really in a financial bind at the time.

By OeKc05 — On Dec 07, 2011

I remember driving around my sister's twenty-year-old Toyota for awhile as a teenager. It was the only vehicle I was allowed to drive, and the air conditioner had not worked on it for years.

I felt a little vulnerable driving this tiny piece of worn out machinery down the highway. I also felt conspicuous, and that was magnified once the AC pulley began to squeal.

I had no idea that it was in any way connected with the cooling system of the car itself. Had I known this, I would have pulled over.

However, I kept going, and the car overheated. I was at the epitome of conspicuousness on the side of the road with the hood raised and smoke coming out.

I stood a safe distance from the car, because for all I knew, it could blow up at any moment. I called my dad, and he instantly knew what had happened. He felt responsible, because he had never fixed the AC pulley.

By Perdido — On Dec 07, 2011

@shell4life – Wow, that is awful! I have heard of squirrels and mice chewing on the wiring inside of air conditioners before, but I've never heard of them getting caught in the pulley. I guess maybe he was on his way to your wires when he got snagged.

My AC pulley started squealing last summer. It was the middle of July, and temperatures exceeded 100 degrees. The bearing needed to be replaced, and unfortunately, the air conditioner repairman was booked up for a solid week.

My dad looked at it and saw what the problem was. He could have fixed it himself, but we have an older unit, and the stores around here would have had to order the part we needed, which would have taken just as long as waiting for the repairman to come.

Being without air conditioning in the heat of the summer makes you appreciate modern technology a lot. That was one of the longest weeks of my life. Thankfully, a breeze blew most of the time, so opening the windows kept us from suffocating.

By shell4life — On Dec 06, 2011

I have noticed that when my air conditioning unit starts up, it sounds very loud. The engine makes a noise like that of a car that needs a muffler being cranked, and for a few seconds, it sounds as if it might explode.

This is normal, though. It has always sounded this way. Once the clutch activates, the engine lowers its volume to a steady hum, and I can hear the AC pulley clicking as it operates.

Since we live in the country and the unit is exposed to wildlife, we have had problems with squirrels. One got caught in the AC pulley and caused the unit to shut down once. I felt terrible for the poor slaughtered squirrel, and I had to call a heating and cooling man to come and remove the carnage.

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