[DML] A/C Problems (necessarily long)

[Jake Kamphoefner <jakekamp@xxxxxxxxxxxxx>]

All,
 
A/C experts, please read!  I've got a really strange issue with my air conditioner that I'd like to properly diagnose before I go replacing more parts.  This is a long post, but I wanted to include all the relevant info:
 
Since I bought 1063, the A/C has always "worked", but the air is never as cool as it should be.  I've also noticed excessive sweating of the evaporator core, even after cleaning the drain out with compressed air.  The most peculiar thing: my compressor never cycles off.  As soon as I hit the mode switch to any A/C position, both my cooling fans and my compressor turn on, and *never* turn off unless I turn the mode switch to vent or above.  This includes, idling, on the highway, cool days, hot days, etc.
 
I've got records for the car back to 1983.  The work was all done by Steger and includes a new NOS compressor (about 5 years ago) with all new A/C hoses.  As far as I can tell, the accumulator bottle, evaporator, and condenser are all stock, but appear in excellent condition.
 
I stopped using the A/C because I didn't want to overwork the compressor or those circuits, but here's what I've tried to do to fix it in chronological order:
 
1.  I sniffed another bottle of R-12 in the system, after someone suggested I might be low on freon.  No change.
 
2.  I put gages on it and found that my low side pressure was dipping into the low teens, while my high side was blowing up way over 300 when the car was revved.  The low pressure switch never kicked off the compressor, so I pulled the plug off the low pressure switch and everything stops as it should.  So I replaced the low pressure switch.  No change, everything on.  Then I tried adjusting the switch to the extremes (both directions) with no change.  I even switched it out with a known good switch with no change.  Rob Grady suggested that I may have a restriction in the system and suggested I replace the accumulator bottle and orifice tube.  So....
 
3.  I bought a new bottle and orifice tube.  I evacuated the system replaced the bottle and orifice tube without damaging any fittings (thank God this car was from California...).  The old orifice tube had a few particles of black gunk on it, but was actually very clean overall.  Then I vacuumed it all down for a long time.  The system held vacuum for a long time (about -29) so there don't appear to be any leaks.  Then as soon as I started the car, with a completely empty and vacuumed down system, the compressor was already cycled on, non stop!  We went ahead and recharged with 2.2 lbs of fresh R-12, with no change in operation whatsoever.  The compressor is still constantly on and the temperature out of my vents was only about 59 or 60 degrees.  Never any colder.
 
4.  Then we suspected an electrical problem.  I got out the wiring diagram and found that my wiring appears to be all stock, with no modifications.  Pulling fuse 10 shuts it all off as it should (we tried this because we thought we might be getting some kind of feedback from the fuse 5 circuit).  We also tried replacing the diode in the electrical compartment (the one between pink and black/orange, I think?) shown on the wiring diagram with no change.  However, this car has never been fitted with a high pressure switch, but it is my understanding that a missing high pressure switch shouldn't cause this weird problem.
 
The car makes all the right sounds (except cycling):  I hear the "woosh" of freon through the evaporator core, the bottle sweats, the evaporator core is cold and the drain drains, the compressor is quiet and the clutch for it engages smoothly.  My blower motor is a quiet NOS that blows a high volume of air, and I have no melting of any fuses in the electrical compartment.  Also, the mode switch appears to be in excellent condition, and I don't believe there are any leaks in vacuum; all air is directed quickly to the right spots,  I've also verified a tight fit of the foam on the back of the evaporator core.  The condenser is clean and still has almost all of it's paint.  My cooling fans work great and flow in the proper direction.  I've also verified that my heater core valve is closed.
 
Ok, so do you have any suggestions for me?  I'm ready to do or buy anything at this point to get the thing to work right.  Does this sound like there is still a restriction some where?  Could I have some internal compressor damage?  Any help you can give is greatly appreciated.  Right now I'm leaning toward an evaporator replacement, but I hear it's an awful job.  Maybe I can hire Dave Strangand to put my car back together after replacing the evap.  :-)
 
Thanks a lot!
 
Jake Kamphoefner
1063 in Southern IL



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