Automotive Air Conditioning Information Forum

Car is a 2003 Mazda Protege5, factory AC with about 182K miles on the clock. Its AC system still works fine - it cools the car's cabin well enough in hot & humid MD, and the compressor seems to cycle on & off when it's supposed to. I've owned the car since new, and the AC system has never needed any service or a recharge. Car was handed down to my kids a couple of years ago.

Anyway, recently I noticed that when the compressor engages, I'll hear a metallic shrieking sound coming from the compressor. If I rev the engine while its doing this, the pitch & volume of the sound increases, but then abruptly goes silent if I rev high enough and bring it back to idle. It stays silent until the next time the compressor cycles itself off & on again, when the noise repeats.

My 1st thought was a too loose or too tight drive belt - since I recently replaced those at 180K miles while I did the timing belt job (DIY mechanic here). So I pulled out the FSM, checked, re-adjusted & re-checked the belts to factory specs multiple times (using both belt tension AND deflection methods!), so I'm confident this isn't just belt noise. Even swapped the old belt back on and there was no change in the noise.

I haven't bothered to connect my gauges to this A/C system yet, so no pressure data to share.

So my question to the experts here is could this sound I'm hearing be the death rattle of a failing compressor and/or clutch? And if it is, would it be smart to do a preemptive compressor replacement (new or rebuilt), pull a vacuum & recharge by weight to prevent potential damage to the rest of the system? For the time being I've told the kids they are banned from running the AC while driving - they'll have to sweat it out till dad can fix this one!

Thanks!

I'd pull the belt that turns the compressor and spin the idler pulley by hand, see if the pulley feels bad or makes a noise, I've had bad AC idler pulley on my Frontier.

If it is compressor making the noise - have a local mechanic you use? If bad compressor, replace before more debris from the compressor gets in the system. You may get away without replacing a bunch of stuff that way.

Cusser wrote:I'd pull the belt that turns the compressor and spin the idler pulley by hand, see if the pulley feels bad or makes a noise, I've had bad AC idler pulley on my Frontier.

Great suggestion, I should have thought of doing that while I was re-checking the belt! Taking that idea one step further, with the engine not running, I can try to electrically engage the AC clutch, and rotate the pulley part by hand in same direction the engine turns. If everything is good, I'd expect the pulley should turn the compressor shaft without slipping, squeaking, or making any noises and it should turn relatively easy - I should just feel some resistance as the compressor does its thing compressing.

Cusser wrote:If it is compressor making the noise - have a local mechanic you use? If bad compressor, replace before more debris from the compressor gets in the system. You may get away without replacing a bunch of stuff that way.

The mechanic will be me, I've restored dead auto AC systems before, so not too concerned there - other than the time-suck & skinned knuckles factor! Given the fact that the AC system cools as well as it does, and the sound is somewhat intermittent, odds are that the mag clutch might be slipping or otherwise buggered up somehow.

I'd also add there's no signs of oily residue around the compressor shaft seal area, or anywhere that oil might get flung out from a spinning compressor that would indicate a failing compressor shaft seal or bearing.

Three years ago the AC on our 2005 Yukon started breaking its small AC belt (separate from the main serpentine belt). After replacing the belt a couple of times, read that low position of compressor on engine caused slugging, and caused belt breakage. And AC worked great until the belt would break, sometimes could hear a chatter noise.

I read up on this, replaced compressor (only) and added an electronic deslugging protector, and has worked fine since. Same accumulator, no flushing, etc., I caught it early and was worth it.

Interesting... I had to look up "slugging" since I was unfamiliar with the term. Still wondering how that might occur though. I suppose that if the system lost a little refrigerant over the years, but not enough to make a noticeable difference in cooling performance, the compressor might become more susceptible to slugging given its location.

The compressor on this Mazda 2.0L is mounted low, fixed to the block. Compressor shares a 5-groove serpentine belt with the PS pump, which is mounted up high. Belt adjustment is obviously done at the PS pump. There's another belt for the water pump & alternator.

If it ever stops raining here, I'll have to pull that belt and do the hand rotation tests and see what's up.

This car has a receiver/dryer, which I've been told should be replaced anytime the system is opened & exposed to the air. Which I'll have to do if the compressor needs to come out for replacement, or for a mag clutch repair/replacement. What's an "electronic deslugging protector" and where would I find one?

http://www.4s.com/en/marketing/psp-solu ... deslugger/

does not work after damage is there

Thanks for the de-slugging gadget link.

Just pulled the belt and hand checked the compressor & mag clutch. When de-energized, the pulley spins smooth & easy with no noises. Energized the clutch with a jumper to +12V and the compressor turns with the normal resistance you would expect as it compresses, but the the motion is very smooth and there were no noises to be heard.

There are procedures in the FSM for checking the mag clutch gap/clearance, which is one of the actions listed in the FSM for troubleshooting AC noises. Unfortunately it requires pulling the compressor and doing the measurements on a workbench, since there's no way to get a dial indicator where it needs to be in the car.

Before I do that, I think the next step should be to hook up the gauges and start measuring temps & H/L pressures, and take note of the H/L pressures when the noise comes & goes, while also capturing engine RPMs. If the noise is due to the clutch slipping/grabbing, I would expect that there might be noticeable H/L pressure discontinuities when the noise comes & goes.

If you can get at the end of the compressor, the gap can be adjusted on the vehicle. Feeler gauges in the gap are all you need.

The gap can be as small as .005" - as long as it does not drag when off. Anything over .030" can cause trouble.


Clutch faces should be clean & dry. Any accessory slinging oil or grease can cause clutch slip & noise if it contaminates the friction surface. Front seal leaks, power steering leaks are common culprits. However I have seen a failing idler bearing in the belt system spit grease in to a clutch gap before.


A spray can of brake cleaner & degrease the gap - if the gap distance checks ok with a feeler gauge.


Even more rare is a broken spring finger on the clutch plate. Inspect the front of the clutch carefully, and make sure the plate is sitting parallel to the pulley face while you are checking the gap with a feeler gauge.