SteveC

My M5 has the automatic climate conrol feature. Although the system
is currently adequately cooling the car for the time being, it is
making some amazing noises and since it's going into the shop
tomorrow for repair of same, I'm hoping someone on the list might
have some specific ideas on the causes so I can point the shop in the
right direction for making repairs.

As the A/C runs, every few moments it sounds like a valve of some
sort behind the dash opens and/or closes and emits a squealing noise
of varying lengths as it cycles. Other times it howls as though a
belt were slipping, although I'm certain the belts aren't (although
I'm wondering if the clutch on the A/C compressor is intermittently
initially locking up when it when it cycles on.

Anyway, this is a bizzare one, and not a sound I've heard before in
14 years of BMW ownership. Any ideas out there? Thanks.

Steve Castle

Derrick E

SteveC,

Your problem sounds exactly like the one I am having. I am almost sure mine is a belt slip on the AC. It sometimes squeaks when I turn the A/C on and squeaks every so often as I am driving. Not sure whether the A/C is locking up intermittently and causing the slip. I was going to just change the belts as it is time anyway and see if that clears up the problem. Let me know if you find out anything more.

Gene Cockrell

Gentlemen, I also am having the same problem: my compressor acts like it is locking up (noisy belt slippage) at anything approaching 3500 rpm, also with most acceleration around town...
I checked system pressure on the low side only (R-12 system) and am getting a significant pressure drop as the engine is speeded up (from ca. 38psi to ca. 20 psi). This indicates a system blockage.
There are two things that can cause this; (to the best of my knoweledge) a bad receiver drier and/or a blocked expansion valve orfice. The a/c system has to be evacuated to replace either of these components, the parts cost about $100 US each, and I'm simply going to replace both at the same time...
BTW the expansion valve is located in front of the center console, kinda near the accelerator pedal.
The problem is that R-12 (Freon) has a truly exhorbitant excise tax here in the US and most shops will want to flush and convert your system to R-134 which entails a greater outlay of money as well as a loss of up to 30% of your car's a/c cooling capacity.

Words to the wise...R-12 costs about $3 USD/can in Mexico and I don't believe there are any prohibitions against importing small quantities for personal use...

Rod

Gene,
I have yet to become an A/C professional, however I don't see any thing grossly wrong with the low side (suction side) pressures of 38psi and a drop to 20psi as the engine speeds up. The pressures on the low side are an indication of outside air temp, humidity and system charge. At the lower temps and humidity the low side pressure will easily approach 20psi in a fully charged system when the evpansion valve is throttling down the Freon flow into the evaporator. Should your system become low on Freon the low and high side pressures will drop also. The best indication of system health is to make low and high side pressure measurements and compare them with a standard Freon R-12 temperature/humidity chart. It is also best to observe the high side sight glass for bubbles/froth under the cover next to the E-box in the engine compartment.
On my M6 the expansion valve failed and closed down completely. The low side went down to 20in-Hg (vacuum) and the compressor just functioned normally(no belt squeal). However, the Freon moving through the compressor is the only thing that cools it and should you run the compressor for an extended time with a closed expansion valve the compressor will lock-up for sure.
The compressor should also be able to push the pressure up on the high side all the way to the pressure cut-out (385psi) with no obvious indication other than the compressor clutch would disengage.
I suggest that should you're A/C belt squeal, I would first check the belt tension, condition of the belt and pulleys. If a belt has slipped for even a short period the belt can glaze on the pulley contact surfaces and require replacement to recover proper traction on the pulley. Should the belt be allowed to slip long term the pulleys will wear and even new belts will not seat correctly and start to slip in short order. Repeated re-tensioning will be required and the belt may glaze before a satisfactory tension is obtained. Then I would inspect the compressor for obvious abnormal internal friction by powering up the A/C compressor clutch without the belt and turn the compressor over in the operating direction, by hand.
Regards,
Rod…

Gene Cockrell

Well Rod, actually I did put all new belts on, tensioned (>1/2" deflection) properly.
I got the squeal when I started using the A/C.
I checked belt tension, then pulled and replaced the a/c belt again and cleaned (lacquer thinner) and dressed (emery tape) all the pullies at installation...
I did all this first with no positive results...Thanks for the ideas though and I'm definitely no professional a/c man...


I'll post when I get this project done...

Rod

Gene,
IMHO, Belt tension is more complicated than deflection of 1/2 inch.
I suspect your belt tension is insufficient.
I have replaced many many belts and I have given up on the feels right method only. I now use a belt tension tool to set the belt tention and recheck the tension(cold) after an hour or so of run-in. The results are more predictable and consistant. New belt tension needs to set higher than used belt tension because the new belt will stretch after a few minutes of run-in and warm-up. The new belt tension and final 90-110 pound tension after run-in is difficult to guess by just deflecting the belt without a reference for the belt size and distance between pulleys. If you are making the tension feel/measurement from under the car then distance between the A/C and crank pulley in the E-34, M5 is short(>12") and 1/2 inch deflection will make the belt very loose.

Rod

I need to correct my last post.
The last sentence should read:
...distance between the A/C and crank pulley in the E-34, M5 is short("less than", < 12") and 1/2 inch deflection will make the belt very loose.