Climate control problem
 

I have '87 MB 300TDT, climate control works fine for the first 30-40 minutes or so after standing 8 hours. After the first 30-40 minutes or so nothing comes out of the vents. The blower cycles to high speed but nothing comes out of the vents. Heating and cooling work fine for the first 30-40 minutes. Need direction where to look. Mario 3

Nothing comes out of ANY vent, or it just blows out the windshield? There is no way it won't blow ANYTHING with the blower running, it's gotta go somewhere (all circuits "off" is defrost).

If you get only defrost after a while, it's time to pull the glove box and check the operation of the temp sensor aspirator motor (below the right hand side vent inside the dash) and the operation of the vac servos that direct the air. Chances are, alas, that the servos are shot and need to be replaced. This requires removal of the center console and some squirming around, detailed by Larry Bible.

I would also check to make sure the 90 degree elbows on the swithover valve beside the heater box (left side of the glove box hole) hold vac.

One other thing to check -- make SURE you have adequate vac to the AC system from the engine. A blown air recirc or EGR transducer will reduce the vac available to nothing, and you will get only defrost flow from low vac. You can check with a MitiVac hand pump (I strongly recommend you get one!).

Peter