Is the compressor about to go out?
 

Hi, all,

I've had my '97 C230 for about 6 weeks now, and am familiar with its normal sounds and lack of same. The A/C has been blowing nice and cold in our New Orleans heat. Yesterday afternoon, however, as I was sitting at a stop light, the engine began to vibrate -- pretty gently, all things considered, but I could feel it in the wheel and shift knob, where even with air on high the idle is usually glass-smooth. Also I can hear a new puttering or purring noise from the engine bay, audible even with the windows up (and quite audible with them down as I drive by a wall or through a tunnel). The A/C remains cold, and seems to perform perfectly.

When I turn off the A/C, the vibration and noise disappear, only to return when I restart the A/C. The car does not stall or hesitate with the air on or off. Temp gauge sits at ~87 C., and the tach is steady at 550-600 or so.

Am I about to have to buy a new compressor? Is it possible that I just need a new V-belt? Or is this noise and vibration normal (if so, why would it only appear now)?

Any advice would be appreciated!

Sounds like you're about to toss the compressor; your speed sensor should start cutting your compressor out before long, but until it does you should continue to feel and hear the compressor getting worse. You might hook up a guage and make sure there is not a blockage on the high side causing the problem, however. If no blockage (I.E. pressures above 300psi w/ the aux fans on), then compressor very likely; keep in mind the friction that causes this vibration will also be causing metal to flake off and travel throughout your A/C system, possibly ruining other things as well.

I'm very curious to know what you find out. Please keep us posted.

Looks like its days are numbered . . .
 

Many thanks to all who posted. I stopped by my usual independent, who worked on my venerable 420SEL for the last 3 years. He lifted the hood and inspected, listened to it with A/C on, off, then on again, and pronounced the dread sentence. "Yeah, compressor's going."

It may not be so bad; he thinks the evaporator and other parts are OK. I'll call him a little later to get a price on the compressor and labor, and schedule it for next week. (He said the A/C should be OK to use sparingly until then, and I'll be parking the car at the airport while I'm out of town this weekend, so it'll be easy enough to do without A/C.)

Three good things, though:
1) This was the original compressor, with 7 years of hard work fighting NO heat. Not too shabby!
2) I'll have him change the cabin filter while he's at it. This may also solve the problem I posted about earlier, the odd vibration from the far side of the dash -- which I realized yesterday does not happen when the A/C is off. He can take a look up under there while he's doing the filter and see if anything is loose or worn. Maybe the vibrations from the ailing compressor are being reflected up the ductwork to the air vent, which seems to be where the annoying noise is coming from.
3) I'm philosophical about it. After all, the rule of thumb is that you should prepare to spend about 10% of the purchase price of a used car in repairs during the first 6 mos. So far I'm on budget!

You mite be able to get some additional info here.http://www.aircondition.com/
Good luck
Rdanz

[QUOTE=Benzadmiral]Many thanks to all who posted. I stopped by my usual independent, who worked on my venerable 420SEL for the last 3 years. He lifted the hood and inspected, listened to it with A/C on, off, then on again, and pronounced the dread sentence. "Yeah, compressor's going."QUOTE]

You may be able to save it by adding some oil to the system. Freon leaks are always accompanied by oil leaking out of the system as well. Since you don't know how many times freon has been added, without oil, it may be dieing for lack of oil.

Don't overlook a noisy serpentine belt tensioner. They have a knocking sound that may be relieved by turning off the AC, which is removing some load from the belt.

Good luck,

Jim in Phoenix

Oil and tensioner?
 

Thanks, Jim. I'll ask him to check that before he starts tearing anything apart.

By the way, the price he quoted me for a factory-rebuilt compressor was $650. There are cheaper ones, apparently, but in his experience they don't last long, and do more damage when they fail. (Kevin has always tried to *save* me money, so I'm inclined to believe him.) And I want to keep the car for a number of years, so . . .