 Rear AC not working on 1993 Aerostar
My rear AC was blowing hot air while the front was cold. Took it to Ford, they said they fixed a vacuum hose to a valve in rear, worked fine for 2 weeks. Started blowing warm air again, took it back, I think I go an idiot for a mechanic this time, says I need new compressor, accumulator, expansion valve, etc (about $850 worth). The compressor blew out some Freon while I was showing them, then it shut off (like a high pressure relief valve). There is only one temp control and that is on the front panel (no rear temp control, just a fan switch in back as well as the one on the front).
I don't believe all these components are bad because the front cools fine even with low Freon after it blew some out.
Here's what I think. I have once replaced the heater valve under vehicle (behind the driver) for a similar problem. I checked the lines when I got it home. I had been running the AC. The return line for the heater should have been cold since the valve should have shut the water off...it was hot, not as hot as the input, but hot. I also noticed where they had cut the plastic vacuum line and inserted a rubber splice (this was their $107 repair).
I believe that either the hot water valve is defective and not closing properly or the vacuum line is leaking someplace not closing the valve, resulting in the warm air. I also believe that because the valve is not closing, it is heating the AC lines, causing them to overheat thus building excessive pressure in the AC lines resulting in a high pressure valve opening on the compressor until an acceptable pressure is reached.
Can someone with AC knowledge confirm or reject this idea? | 
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