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....