question for A/C experts - PeachParts Mercedes-Benz Forum

cbjukraine · #1 05-30-2012, 08:41 PM

I've noticed my R4 compressor making a weird continuous pfft-pfft-pfft sound from about 1500-2500 RPM. After that the engine noise just drowns it out. It sounds somewhat like a very rapid-fire air pistol or paint-ball gun. That's the best I can describe it, as the sound is not a rattle or clank.

Any ideas? Do I need to look forward to replacing my compressor again?

cbjukraine · #2 05-31-2012, 12:58 AM

I could also describe the sound as a muffled click...

cook · #3 05-31-2012, 08:48 PM

I am no expert, but is it the same sound with the compressor running or not?

Air&Road · #4 05-31-2012, 09:46 PM

What are you pressures at what ambient and vent temp? That would be important to know under such circumstances.

cbjukraine · #5 05-31-2012, 11:19 PM

As I am on my own on this, it's hard to get all this information at one time. I can say that as of right now, the system is cooling wonderfully.

On monday, at about 95 degrees outside, I was getting 40-42* vent temps rolling down the highway (when I first noticed the click/tap sound).

I just checked the pressures today and was getting around 250-275 psi high side and around 25-30 on the low side at about 2500 RPM. This is sitting in the driveway at about 85* ambient temps. Of course that's the outside air temp, the engine bay temp was about 95*. Don't know if that matters.

It is definitely the compressor, as the sound goes away when the A/C is disengaged. I can hear the sound clear as day with the driver's window down whenever there is a curb or barrier to the left of the car to bounce the sound back to my ears. The sound stops immediately when the A/C is disengaged.

Air&Road · #6 06-01-2012, 08:13 AM

Under those conditions, those pressures sound very good. When the car is rolling, getting ram air, that high side pressure is lower than that. These are not excessive pressures, certainly not to the point of overstressing the compressor.

Since I'm not there to hear it, it's difficult to say, but I believe I would drive it and turn up the radio volume if necessary to drown out the racket.

Keep us posted and don't lose sleep over it.

Best of luck

vstech · #7 06-01-2012, 12:43 PM

Quote:

Originally Posted by cbjukraine

As I am on my own on this, it's hard to get all this information at one time. I can say that as of right now, the system is cooling wonderfully.

On monday, at about 95 degrees outside, I was getting 40-42* vent temps rolling down the highway (when I first noticed the click/tap sound).

I just checked the pressures today and was getting around 250-275 psi high side and around 25-30 on the low side at about 2500 RPM. This is sitting in the driveway at about 85* ambient temps. Of course that's the outside air temp, the engine bay temp was about 95*. Don't know if that matters.

It is definitely the compressor, as the sound goes away when the A/C is disengaged. I can hear the sound clear as day with the driver's window down whenever there is a curb or barrier to the left of the car to bounce the sound back to my ears. The sound stops immediately when the A/C is disengaged.

... bad aux fan?

the pressures are odd, high high, and low low...

what refrigerant is in the car?

tangofox007 · #8 06-01-2012, 01:06 PM

Quote:

Originally Posted by vstech

... bad aux fan?

The aux fan doesn't engage/disengage concurrently with the compressor.

vstech · #9 06-01-2012, 01:09 PM

I agree, hard to pinpoint this one, good cooling, low pressures, clicking noise... bad clutch would be my guess, but it should not be clicking if it's cooling... perhaps, the belt is slipping? maybe the low pressure switch is bringing the compressor in and out at speed on the highway.
do you hear the clicking with the hood open, sitting at idle?

cbjukraine · #10 06-01-2012, 02:22 PM

the refrigerant is r134 with PAG150 oil. 3 cans (36 oz) of refrigerant and I'm not sure how much oil, but at least 6-8 oz. I would say.

I cannot hear the clicking noise at idle with the hood open. If I rev the engine with the throttle linkages, it kicks in at about 1500 RPM, and gets more rapid and lounder with higher RPM. I can faintly hear the noise at highway speeds with the windows up, but it's there.

Testing in the driveway with the hood up, I can see no erratic engaging/disengaging of the clutch causing the noise. The noise seems to be too constant for that to be the cause.

Should I try removing the belt and seeing if there is any play in the clutch?

I'll try to get a recording of the sound and post it.

Air&Road · #11 06-01-2012, 02:37 PM

OOooohh........... I'm not paying attention. I didn't corelate this with your other post indicating the three cans of 134. It's VERY easy to overcharge a converted system and I fully expect that 36 ounces of 134 is too much for this car.

Start with 60% of the R12 weight in 134 and add in SMALL increments from there. I've seen systems that operate VERY well on as little as 60%.

I thought we were dealing with an R12 system.

vstech · #12 06-01-2012, 10:40 PM

Quote:

Originally Posted by cbjukraine

the refrigerant is r134 with PAG150 oil. 3 cans (36 oz) of refrigerant and I'm not sure how much oil, but at least 6-8 oz. I would say.

I cannot hear the clicking noise at idle with the hood open. If I rev the engine with the throttle linkages, it kicks in at about 1500 RPM, and gets more rapid and lounder with higher RPM. I can faintly hear the noise at highway speeds with the windows up, but it's there.

Testing in the driveway with the hood up, I can see no erratic engaging/disengaging of the clutch causing the noise. The noise seems to be too constant for that to be the cause.

Should I try removing the belt and seeing if there is any play in the clutch?

I'll try to get a recording of the sound and post it.

ok, you have pag oil in there in unknown quantity... did you flush out the entire system prior to putting in the pag? did you change the txv? dryer?
please tell us exactly what has been done to the car.
thanks.

vstech · #13 06-01-2012, 10:42 PM

yeah... 36 oz is more than you would need of R12... you should have more like 20 oz in there...

cbjukraine · #14 06-02-2012, 03:59 AM

here's the rundown on what's been done.

1) Changed the compressor as the suspected cause of my leaks. I was having to add a 12 oz can about 2 times per year to keep the A/C working cold.

2) While changing compressor, flushed all lines, evaporator, and condenser with aerosol can A/C flush and shop air. Added almost 8 oz PAG150 oil to compressor and system during compressor install after flush.

3) System would not hold a vacuum, so I took it to an A/C shop. They inspected for leaks and found none. Knowing now what I know, I will never return to those idiots.

4) While charging the system with r134, the compressor blew in the same manner as Bruce Bonds experienced

5) Purchased new compressor (got a refund for the old one) and had the same A/C shop install and charge system. I can only assume that they put the right amount of oil in, because a lot came out of the blown compressor. After a week, all refrigerant had leaked out.

About a month later...

6) Turns out, the leak was in the evaporator. I removed the evaporator/heater box (not as bad as you might think) and found the leak in one of the u-bends on the evaporator. Replaced the evaporator with a solid junkyard unit, pulled vacuum for 24 hours, held vacuum for 3+ hours, so I charged with 36 oz of r134 and about 2 oz PAG150.

That brings us to the present problem of the noisy compressor. Cools great, just makes an awful noise. I'm just concerned the compressor is going to seize, then I have to start all over again.

Air&Road · #15 06-02-2012, 05:57 PM

I think that it is clearly overcharged. What is the specified amount of R12 required for the system? Whatever it is, multiply that by .6 and start with that weight in R134. With the PAG oil it's pretty much too late to convert back to R12.

Also, from the sequence you may very well have too much oil in the system as well. If you get WAY too much oil it can cause a compressor to lock.

A highly experienced and savvy pro that used to be a frequent poster here put in these words once: "insufficient oil wears out compressors while too much oil destroys compressors."

Hope this helps,