79 450SL A/C Failure Mode - PeachParts Mercedes-Benz Forum

RomeroAG · #1 07-14-2004, 12:59 PM

I own a 79 450SL and the Automatic Climate Control is giving me trouble....again. The only way I can get the A/C to run is if I press the top (defrost) button. The compressor comes on and cold air comes out of the defroster ports. However, the unit will not run in any other mode and the compressor will keep running whether I have the a/c compressor switch on or off. Sometimes after running in defrost mode for several minutes I can switch to the low A/C button and the unit will run (again cold air with the fan now in low mode) but that is it. If I roll the thermostate...I get no change in air temp. Cannot get it to go into heater mode no matter what I do. The only thing I can think of is I had a dash pad installed and the techs could have fiddled with the temp sensor in the process. Any thoughts? Thanks in advance.

ctaylor738 · #2 07-14-2004, 02:43 PM

Take the glove box out and make sure that all the vacuum elements are connected. In any position but DEF, the flaps, which are moved by vacuum, must be in the AC position before the system will turn the compressor on.

The dash guys may have knocked a line off.

RomeroAG · #3 07-14-2004, 04:36 PM

Thanks - will try that. Could anything else be causing the problem. The reason I ask is I am deployed overseas and have the car in storage and would like to fix the problem when I am back on leave next month. Thanks.

ctaylor738 · #4 07-14-2004, 10:39 PM

That's my most likely scenario. It is also possible that the in-car sensor - the one in the middle of the dash - got knocked loose. But you would think the compressor would come on if that happened.

Hope you're safe where you're deployed.