No A/C or fan in drive and neutral

I've been chasing a no A/C and no blower problem. With no success. Today I put the car in reverse hit the gas, and miracle of miracles freezing cold air and the blower works on all speeds!!! I put the car back in drive and nothing... I repeated it several times and it was the same result over and over again. Has anyone else had this problem? Did you find a fix? Does anyone have any suggestions? Thanks, Guy

I'm certain there is a wire or wires that supply the a/c and blower motor. However without a service manual or wiring diagram to trace the appropriate wire traces I'm at a loss. Thanks, Guy

The only two things electrical connected to the transmission that I can think of are the backup lights and the neutral safety switch. Since it does when switching from reverse to drive, I would suspect the backup light switch first. 

By chance does anything else suddenly work while in reverse??....  do your gauges or dash lights work correctly?  usually funny things like this is a grounding issue, but this is kinda weird....  gotta a link for 1979 wiring, which "should" be the same, doesn't always work that way, but usually they are same/similar unless some major change happens in manufacturing.

Thanks for the reply, Jim. It'll be really helpful. Guy

welcome, keep us posted... we like a good mystery around here... hopefully not a murder mystery..... but, i know the feeling of wanting to shoot one of these things and bury it out back in a shallow grave.... but ummm, you didn't hear that from me...   ;)   

You can view and/or download any of the '68-'82 wiring diagrams from my web page.

1968-1982 Corvette wiring diagrams

I would be looking for a bad engine mount that is allowing the engine to raise up somewhat in reverse, which can cause the wiring harness to move enough in some cases to either make or break contact in some circuits. The blower motor, and the A/C compressor circuits are completely separate....one should not effect the other. From the sound of it, you have a wiring issue in the harness on the passenger side of the engine compartment, or possibly in the fusebox pass-thru on the driver side, where the front engine and lighting harnesses connect to the fusebox. Sometimes just disconnecting and reconnecting this connector can fix all kinds of goofy problems like this.

Wow! Great stuff. Thanks, Guy