Just "inherited" a 1981 300SD, in good shape. AC worked for a couple days, then hot air. Compressor seems to come on and everything. Freon seems OK, but no cold air? We disconnected the relay near the canister. Compressor definitely engages, but HOT air. What is weird is that if I'm driving for a while, turn it off, then start it again and turn on the AC - it is cold for a second, but only a second. Any ideas? BTW I live in Phoenix..it's 104 degrees..I'm melting...help....

Do a search and read up on the climate control pushbutton unit, mono valve, evaporator freeze protection and vacuum diaphragms. You will need to troubleshoot the system - these are some of the important parts of this system that can cause problems like what you are describing. The positive is that it does blow cold - that indicates that the compressor system is ok.

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Jim

I received some diagnostic information on climate control systems from Larry Bible. If you want to e-mail me your fax number I'll fax it to you or I can drop it in the mail. It should help you out or at least help you narrow some things down.

JCD

my FAX is 480-967-7799.

What is strange is that the defroster works great, the fan works, if the car is in the shade (even at 107 degrees) the air that comes out is still 10 degrees cooler than ambiant air temperature? What is up with that???

I left the tech documents at home. I'll "try" to fax them tomorrow.

JCD

Thanks. Thank GOD it's now below 100. Whew! So it isn't so bad. Still need to fix it though.

Again appreicate all the help

Larry