W126 - A/C works for about 30 minutes, then stops.
 

Hey guys, A/C question. The A/C on my moms 88 300SEL is ice cold for about 30 minutes of driving, then it stops and blows out warm musty air. She asked her cousin who works on car a/c's and he said it could be the evaporator drain could be clogged causing water to freeze up and not blowing out cold a/c. If you leave it off for awhile, it will start blowing cold again. We never see any water leaking under the car.

I read about these leaking inside of the car, but the floors are never wet and it dont seem to be leaking in the car.

My one other question is I dont know where the drain is under the car to see if its clogged if thats the case. Its very hot here and she needs A/C. We may have to end up taking it there and get him to work on it, but wanting to see if its something we can take care of first.

Thanks.

Yes, a clogged condensation drain will indeed cause the problem you describe. Let the car cool off, raise it safely and get underneath. Look above the front of the transmission and you will find the condensation drain in this area. Carefully clean it out with a coathanger or something. If doing so brings forth a gush of water, you will know that this is your problem.

It does not necessarily leak water on the floor if the drain is plugged up.

Hope this helps.

Thanks Larry! We will check that, hopefully thats the issue.

When the problem happens I would look to see if the compressor is still turning. If the compressor speed sensor goes open (which it might do when hot if there was a cracked wire) the klima relay will kill the compressor until you cycle the key.

-J

Good advice from CompU.
On the 126 there are two drains, located on either side of the tranny, coming out of the center tunnel; check them both. They are a flimsy foam-spiral wire spring-looking thing, and tend to age and come apart.
Here in Dallas it's still pretty humid, and my 126 will drip a lot of condensation water. When the wife swings up the driveway after a 10-mile drive, it leaves a trail, and then a 1-foot-wide puddle in the garage.

DG

Thanks for the replies. Well we drove the car today to take my nephew to therapy (it dont get driven too often) and was driving from the house to our destination on the highway for about 45 minutes and the A/C was COLD and it was in the lower 90s outside. We stopped and parked the car and despite the A/C still being cold, there was NO drips of water coming from under the car. I looked when we stopped and again 45 minutes later when we came out. Turned the car back on and the A/C would not work again, it never got cold, the compressor never came back on. :(

I turned it off and on several times as we headed back and it just wouldnt work. I am thinking if it was the drain clogged that it would have not worked all the way down there, then not work after the car had been setting for 45 minutes? I am not sure. We may have to end up taking it to the shop.

Thanks again.

Sounds like you have more than one problem. The drains are likely stopped up or you should have seen some condensation under the car. The system not coming back on might very well mean that the compressor rotational sensor did not stay actuated. This could be due to several different things.

Check your belt if its too loose can cause this issue, if its loose maybe tensioner needs replaced if wont adjust or stay tight

Well to update, my mom took the car to her cousins shop (he specializes in car A/C's) and he checked everything! The car was full of freon. His findings led him to believe that it was the HVAC panel inside of the car that was the problem, at least I hope that is what it was. A brand new one was like $1000, so he bought a used one with a 1-year warranty for $50 off of the internet. He said he would call when it came in and would install it. Hopefully this will take care of it once and for all.

Before you replace the AC head start looking at the Klima (compressor control) relay...

-J

I agree. Second gen headunits are far better than the first gen units.

my 95 w124 has this problem as well. It's good as long as it's running then I stop the car and come back and warm to hot air came out. Freon was checked and good. Then about 3 years ago...an indy mercedes mechanic noticed the compessor was stuck, so in a pinch he gave it a whack and presto....it spun. He then carefully sprayed to penetrating oil on the outside of it. Well...it just got stuck again tonight (MN was 96 degrees and muggy today). Ice cold on my 25 min commute, then I ran into costco and hot air was blowing out when I restarted my car. I went under the hood and saw the center part on the compressor was not spinning again...so repeated the whack(light tap)...used a long 18 inch flat screw driver and gave it a tap....then it spun again. I carefully dripped some penetrating oil while avoiding getting belt while the compressor was running and when the car was off. I just tested it the past 2 hour and it works like normal again. I report back if it goes belly up.
Anyone know how tough or approximate cost to change the compressor alone?

Thanks. Well I told my mom about this (she had taken the car to the shop for the repair - which as stated before is her cousins repair shop) and she said he had already checked that and then ruled out the control panel. He found a used one on ebay for $59, so I guess if for some reason that is not it, they are not out all that much. I am hoping that is what it is. I will report back as soon as the part comes in and is installed on the car, probably one day next week. Its supposed to be in the 100°-102° range this weekend, so I am sure the car will not be driven this weekend. lol.

Thanks again!

a partially shorted compressor clutch coil will also cause the klima to cut of compressor.
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I dont know, he said he checked everything and ruled it as the control panel... I sure hope so, its supposed to be 100°-103° for the next 4 days, she needs A/C! If not, will have to keep driving dads truck. lol.