Just took my car into an indy shop to get a 134a charge and to check for leaks. The mechanic filled it up, but a/c still blows warm air. The compressor and clutch, etc. all seemed to be engaging, but when he checked his guages, the low side readings were too high, and the high side was too low or barely showing any pressure. He did clean out the system before recharging the a/c.

Is my A/C compressor bad, and I have no choice but to have it replaced, or could it be something else?

FYI, it's a 99 clk320, purchased April 03 from some private dealership in VA. (I live in NY) Only work done recently was 60k service. They did have to replace a cracked pipe leading to my intake manifold, but nothing else. My check engine light also just came on (bad MAF), but the mechanic doesn't think its related to my A/C woes.

Wifey is NOT happy....

Be absolutely sure the clutch is engaged!

If it engages and the pressures move some when it does engage, then the compressor is a likely candidate. The compressor is a variable displacement type. That means it doesn't ever shut off to control evap temp. The way it controls is that internally a device like a POA valve maintains evap pressure by reducing pumping capacity. It does that by decreasing the angle of the wobble plate.

BTW POA stands for pilot operated absolute which used to sit in front of the rest of the device called a STV. So the whole device is thus called a pilot operated absolute suction trottling valve. It maintained evap temp by throttling the suction at the exit from the evap. Now similar control is inside the compressor.

Pressures as you state are usually due to lack of pumping capability.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thank you stevebfl for the quick response.

The clutch did engage, and the pressues did jump a little bit whenever the A/C was cycled off and on. As I recall, the low side would jump to approx 300 and the high side to approx 125 when it should actually be the other way around...

Well, just came back from getting an opinion from a Benz specialist shop and say that the issue is instead a bad evaporator core.

That's it,... the start of my divorce...

A conservative estimate was approx $2400, since it's an $800 part and several days worth of labor. For those without warranties... learn your lession vicariously from me,... and go and buy one before it's too late!

This thing was working fine just last year, and my car is only a 1999 with 60k miles. Do these things break down that easily or do I just have a lemon?

Did they charge it up and put dye in it and verify that fully charged the system works and allow positive verification with a black light for the diagnosis.

I would get a second opinion of any evap diagnosis that isn't verified by a dye test. My best guess is there are at least twice as many evaporators replaced to CYA as for real leaks. it is a hard call as it is no where near being viewable. The dye gets carried out of the drains by the water and is proof positive of a diagnostic. Once inside the case the absolute leak can be verified with the dye, sometimnes preventing further problems.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician