Re: Air-con clutch going bad?

Question

The AC compressor has an electric clutch that connects the pulley, whichalways turns when the motor is running, to the compressor. Check if this isavailable separately from Subaru. When you bring the car to them, have themlisten to the noise, since the car will be warm at that point (put AC on,fan at full speed to cycle the AC more quickly. It might make less noise atidling speed, though, since the motor is turning slowly, but you can pushthe throttle or step on the gas to increase the speed).

Steffen Kluge · Accepted Answer

According to ed :That's good advice, thanks.In fact, I only ever noticed the noise while the engine wasidling (usually when I got out of the car to open the garagedoor).CheersSteffen.

Bill Putney · Answer

Don't system pressures (and therefore compressor torque demands) go up at idle (since the system will try to deliver the same BTU's but at lower speed)? Also, at higher rotational speeds, the clutch and compressor rotating parts act like a flywheel, so the belt is less likely to slip to carry the compressor thru the pulse torque loading that it sees.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Edward Hayes · Answer

The compressors I've see with gages attached show the head pressure higherand stabilizing at ~ 1500-2000 rpm. The pressure tries to equalize betweenon/off cycles. Ed

Bill Putney · Answer

Since you seem to have hands-on experience with this, I will defer to your experience. When I had an a.c. hose on my '86 GL-10 wagon burst a couple of years ago when it had been idling for a period of time, I was told that the hi-side hose pressure goes up during extended idling.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Edward Hayes · Answer

I hear what your saying Bill but, I just reported what I observed. I do knowthat some air cond systems use a ? variable orifice valve to smooth-outpulses but, I doubt Subaru systems use it. I'm not sure about yourterm"system pressure" I was reporting on compressor head pumping pressure.The gage reading therefore is showing the average head pressure and not theindivual pulses. It would seem (neglecting temp) that the faster thecompressor runs the higher the gas flow & pressure, and conversely thehigher the throughput as the suction side is also moving more freon. Makeany sense? It seems to to. Ed

Bill Putney · Answer

Sounds good to me. Yes - I was referring to average head hi-side pressure.

What I was trying to say is that from a purely theoretical aspect, if the system is operating closed loop, at idle (because speed is lower), hi-side pressure should have to go up in an attempt to put out the same BTU's (since total energy output is related to the product of rotational speed and pressure, so if lower speed, pressure must go up; higher speed, pressure goes down in a closed loop system). I don't know if this translates into real world automotive a.c. design though. I know that I have heard auto a.c. mechanics say more than once that the system pressure (again, I assume that means hi-side head pressure) increases at idle (and, again, why my hose blew out at idle rather than at highway speed).

I only mentioned the pulses as an additional effect on belt slippage in relation to lower compressor speed translating into less flywheel effect from the clutch and rotating parts of the compressor, and therefore more tendency of the belt to slip at low speeds from that (pulsing) effect.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Edward Hayes wrote:

Edward Hayes · Answer

I would agree that "peak head pressure"    would go up at low speed. Thatmakes sense as the individual pulses must look like a sine wave. At islepeak pressure would be higher during a pulse?? Ed

Re: Air-con clutch going bad?

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