My 300ZX runs hot air all the time. My ac is full of freone and I still get no cold air. Any thoughts on how this can be resolved?

 

Welcome to ZDriver!

Step 1: With engine running, turn on a/c, look at a/c compressor pump. Is the outer part spinning? If not: a) R12 pressure is NOT correct b) compressor wire is disconnected c) compressor is seized

So... check those things.

 

what nismo said but also you need vacuum to close off the coolant valve into the cabin. blown out vac hoses are usually the cause of hot air coming in all the time. get the fsm from xenon. then read it.