A/C stopped blowing cold suddenly, happened last year as well - PeachParts Mercedes-Benz Forum

86560SEL · #1 06-07-2011, 05:22 PM

This episode is exactly what happened last summer. We take the car out, the A/C is fine until we turn the car off, then restart and it blows out heat.

Today I took my mom and nephew on some errands in her car (88 W126) and the A/C was fine all the way to the hospital, then again when we left, we went through a drive-thru for a drink, then to the bank, it was fine. Then a mile down the road, stopped and got some gas and when we started off again, the A/C would not blow cold air... it was warm/hot. The compressor never came back on. I let it run (where the A/C should be on) all of the way home and it never got cold. Pulled in the drive, popped the hood and the compressor, nor the auxillary electric fan were working. I dont know what happened. Seems like this did this last year, so we never tried it again, but the other day when we went to recharge it (thinking it was low, which it was), it was kinda blowing cool and the aux fan was on.

Mom is getting a new car in a couple of months hopefully, but was hoping to get a little more comfortable service out of this old Mercedes until then, without spending a fortune, but thats how it is when you have an old Mercedes. We cannot complain though, we have had the car for 4 years and its only had one issue other than the fuel gauge issue, so its been an awesome car.

86560SEL · #2 06-07-2011, 08:35 PM

wondering, could have have possibly overcharged the A/C? I dont think that would cause the auxillary fan to stop as well?

Also there were visible air bubbles in the sight glass up through the last can of R134a added.

86560SEL · #3 06-08-2011, 09:46 PM

No one has had this issue?

ken1 · #4 06-09-2011, 04:15 PM

My 1990 300 sel does the same thing. I can usually shut off the engine and restart, then it will blow cold. I asked the same question on the forum about a year ago with no response.
I'm still looking for the answer.Ken

tyl604 · #5 06-09-2011, 04:19 PM

Sometimes my 81 300SD climate control will lose its mind and start blowing hot air. Generally I crank it the therostat wheel all the way to HOT for 5-10 seconds and then crank it all the way back to COLD and after a minute or two it will start blowing cold again. My guess is that the sensors inside cause the problem - but it does not do it often enough to be a problem, maybe twice a season.

JimFreeh · #6 06-09-2011, 05:59 PM

Quote:

Originally Posted by ken1

My 1990 300 sel does the same thing. I can usually shut off the engine and restart, then it will blow cold. I asked the same question on the forum about a year ago with no response.
I'm still looking for the answer.Ken

Ah, the microsoft solution..

Shutdown, restart.

Jim

JPMOSE · #7 06-10-2011, 03:40 PM

If the compressor stops working (clutch disengaged) intermittently, it could POSSIBLY be the A/C relay. If there is sudden hot air while the compressor remains working...I would suspect a faulty mono valve (which can rebuilt easily).

cheeseraid · #8 06-10-2011, 04:13 PM

It's the sensor on the cylinder head that has two plugs. Thats the one for the ac. If the car gets over 110 it will shut off the ac. It will not come back on unless you reset the key. Change that and should be good.

JPMOSE · #9 06-10-2011, 05:22 PM

Before you go changing that sensor, please test it first! If it's stuck closed, the auxiliary fan will run continuously, even when the engine is cold. It can be identified by looking for a brass sensor with green plastic in the center...also has two plugs going to it. On the 560 engine (M117) the sensor is at the front of the engine, slightly to the passenger side.

cheeseraid · #10 06-10-2011, 05:27 PM

True but not exaclty true. I know I replaced mine 2 times now. It will misread after use. I can't remember the refrence value in ohms I have it on my laptop. The only thing I can think of other than that is the klima module in the car.

JPMOSE · #11 06-11-2011, 06:55 AM

Well your solution sounds like Ken1's problem. I am focusing on 86560SEL's problem since they're the one that posted the original question. I hope we both can solve their problems!

Bandonbound · #12 06-11-2011, 04:01 PM

Next time it , the a/c, shuts off, push the Defrost button and see if it energizes the compressor. Eliminate the push button assy. to take it out of the mix. Also, does the whole climate system shutdown or just the compressor.
Too much freon, gets hot, shuts down via the hi press switch. Self A/C charging with cans usually this culprit. Gauges will sure help, hi and low numbers. Any shop would charge you a minimum just to check the numbers.Well worth it. NOT a green and red hand held from Pep Boys etc.
Could your expansion valve be getting dirty, and not flowing. Just thoughts.