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-   -   86 300E, love the car, HATE THE A/C (

Nick Jamal 05-08-2000 01:22 AM

Well, after several years of ownership of two 124s, I have come to regard these (so-called) "climate control systems" with a mixture of frustration and fear. It's not as poetic as it sounds...

Although I've received help on this topic before (thanks Benzmac and MBDOC), I have some more details to add, so I hope you'll bear with me.

The AC was inoperative when I bought the car (mistake #1). I took it a friend of the family with an AC shop (mistake #2). After having invested about $1000 in parts with this guy and dozens of hours in diagnosis, I let him "finish" the job. Eventually, the compressor, condenser, receiver/dryer, and the pushbutton control unit were all replaced. The AC had the habit of cutting out and not reengaging until the car was restarted (difficult on the highway...). Thought I had that one solved with the relatively recent replacement of the belt tensioner damper, but no. Well, here are the symptoms, and I apologize for the length of this post.

At any ambient temp, car stationary:
-the compressor cycles normally when idling
-compressor cuts out if revved momentarily to ~2000rpm and stays off for ~10 minutes before reengaging.

At moderate ambient temp (~21degC), while driving:
-AC operates fine, even though 2000rpm is frequently achieved

At higher ambient temp (~25degC), while driving:
-AC cuts out indeterminately (read: I can't always judge when), and then stays off for 5-15 minutes while I lose 5-15 liters of sweat.

I'm at my wit's (and wallet's) end with this problem. The belt tension seems fine. I should add that the compressor is aftermarket and that the pressures have been checked by a MB dealer. Really appreciate any and all input from you kind souls. Will mail cheesecakes.


[This message has been edited by Nick Jamal (edited 05-08-2000).]

[This message has been edited by Nick Jamal (edited 05-08-2000).]

Ted2222 05-08-2000 12:35 PM

Hey Guys, perhaps I shouldn't butt in on this one because I am certainly no A/C expert, but in reading the post, it occurred to me that perhaps the auxilary fan(s) are not running, turning the system off because of the pressures being generated.

Can one of the experts address this question?

1979 240D

Nick Jamal 05-08-2000 01:07 PM

The aux fan runs fine and comes on at ~100deg. The car never went over this temperature during the "testing" as described above. In day-to-day use in hot weather, the coolant temp will sometimes get up to 110 or even 115, but the AC will not necessarily quit even then, and the auxilary fan will kick in. As an aside, in cooler weather, the aux fan kicks in at around 100 and brings the temp back to around 90. In hot weather, the fan kicks in at 110 and brings the car down to 100. This doesn't strike me as efficient. How can I have the fan continue to run until the temp cools to 90 or so?
The dealer also performed a socket box test, results being normal.
Thanks for the responses thus far.

[This message has been edited by Nick Jamal (edited 05-08-2000).]

ctaylor738 05-08-2000 02:02 PM

I am no AC expert either, but I recall that there is a pressure sensor that cuts the compressor off if the refrigerant pressure gets to a certain point. If this is malfunctioning, it could cause the problems that you describe.

I had a 928 that you had to start with the AC on if you wanted it to work. You could not turn the AC on after the car was started. This turned out to be the pressure switch.

I sympathize with you. I just bought a 300E with dead AC.

Please advise us of progress.

Chuck Taylor
Falls Church VA

Benzmac 05-08-2000 09:51 PM

The aux fans should come on with high pressures on the A/C. If over 240, the fans should be on. To check, just bridge the two wires at the drier that come to the red switch. (I hope you have a red switch, it could be green, if so, it should be updated).

If the fans work, the other switch should be checked. It has two functions. It will open if the pressure drops too low, but it will also open if the pressure in the drier is too high. I have seen these malfunction.

To check, you have to find the input and the output. You probe the output and watch. If the compressor turns off and the signal is there for on, you have another problem..(like the compressor control unit.)

It goes like this. pushbutton-drier switch-compressor controller-compressor. This is the logic chain.

Donnie Drummonds
1992 500E (very soon I hope :)
1981 280GE SWB

Nick Jamal 05-09-2000 02:51 PM

I do have a green switch, so I suppose I'll start by updating that. Can you provide a part #, if possible?

ctaylor738 05-09-2000 10:24 PM

You should use the PartsShop on this site to order the part!

Chuck Taylor
Falls Church VA

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