I've an '87 300 SDL that I bought recently that appears to have some A/C problems. The shop I bought the car from has been great, but I feel bad about taking the vehicle back several times after they have put several (probably expensive) parts in it to no avail.

The air conditioning works fine until the car has been running 30 minutes or so, then warm (heated) air starts to come from the vents. Turning the thermostat down a little fixes the problem for awhile, put before long the heated air shows up, and you are cooling the car too much to prevent the heat from coming on.

If this isn't odd enough, the warm air only goes to the front driver/passenger. The register in the rear sends out cooled air regardless.

A new pushbutton/thermostat wheen has been installed, I think an A/C relay, still no help. Any ideas out there?

Thanks-

Welcome to the forum!

I'm no expert in this area, but I've seen some threads with the same complaint.

Try a search on A/C or air conditioning, or vents, etc. Perhaps the solutions outlined on those posts will also rectify your problem.

Good Luck!

One cause of unstable ACC temperature control in a W126 is a deteriorated Aspirator tube. This tube runs behind the glove box liner and pulls air through the temperature sensor (located behind the small grate in front of rearview mirror) With the AC running hold a small piece of tissue paper in front of the grate,it should be drawn against the grate. If not replace the tube with small AC line insulation (black foam tube)available at most home improvement stores.

Bob D.

i wold aso test the monovalve to see if functioning correctly.maybe it is not closing giving you heat all the time

just my.02
James