tliang

I recently bought a 1995 W124 E220 Masterpiece. It has dual zone auto air con which provides excellent ride as well as giving me a headache from time to time.

What can cause the air con to stop blowing cold air in the middle of driving especially in raining weather? This has happened few times. My solution was to pull over the car and restart the engine, then the air con works perfect again. Why? Does anyone experience this before?

The MB tech said my air con worked fine and could not find any problems. Everything else works fine too, no overheat, no fuse burnt, etc.

What's wrong with it?

Jackd

Your problem is most likely caused by a vacuum leak somewhere in the heating/cooling system.
All the traps under the dash controling cold/hot air flow, vents, defroster ands heater are controled by several vacuum servos. A loose vacuum line/cnnector is probably playing tricks.
Another possible cause would be the ''mono valve''. Any defect, loose contact or malfunction defaults the valve to ''fully open'', which means heat in the cabin.
Good luck

tliang

Thanks for quick reply. But I had the car checked in MB shop several times and they found no problems.

Let's say if I will bring the car in again tomorrow, should I ask them to check the possible vacuum line/connector leak as you sugguested or how do I persuade MB teck to tackle the problem?

If it is all under the dash, would it need days to check?

vinamg

Belt slippage. AC has a safety system that compares engine rpm to compressor rpm. If the rpm doesn’t match it will disengage compressor clutch.
Have your mechanic adjust the serpentine belt and double check tensioner for defects.

prossech

I had the same thing happen to my 300E....never gave me a problem until I would drive in the rain.. then it would cut out seemingly at random until I could restart the motor and it would work fine for a while again. I assumed it was a loose serpentine belt and I kept tightening the tensioner adjustment a little more each time it happened hoping this would cure it. It didn't and I finally broke the the tensioner adjuster by over tightening. When I was replacing the tensioner adjuster I noticed that a chunk of ribs were missing from a small section of the serpentine belt. I replaced the belt and the problem has never occured again.

tliang

Serpentine belt? I'll talk to the MB tech.

Thanks a lot! I'll come back for result later.

This is truly a nice place for beginners.

TygGer

Could this problem be related to the vacuum line that goes behind the instrument cluster? What is that for btw?

shadowgriffen

I dont know about later models but I had the same problem with my 88 TE(fan would come on and would shut off and not work again) and all I did to cure the problem was replace the 30A fuse located outside the fuse box.

Now though, I've developed another problem with my HVAC. It will not shut off no matter what I do...remains on all the time and it's getting on my freakin' nerves...

mgw_300e

Could be worse - it could be OFF all the time...

shadowgriffen

+5

shdoug

Another possibility is that it is slightly low on refrigerant and short-cycling on the low pressure switch. The system may be smart enough to limit the amout of short-cycling by locking the compressor off until you reset it. Most commercial A/C systems have this feature to protect the A/C compressor. Short-cycling can cause the compressor to run short of oil by not running long enough to allow the oil to return. I kind of doubt the car is that smart, but it's possible. Driving in the rain will lower the head pressure which in turn lowers the suction pressure and if there is a shortage of refrigerant this could cause a problem. I have not had a chance to drive my car with the A/C yet because it's been so freaking cold but when I do I will figure out how it operates.