A friend was parting a '70 New Yorker out and offered me any parts I might desire. It was an ATC car. I was interested in why there was a metal screen in the intake side of the compressor line AND why it had a male wire terminal on it???!!! Like some sort of ground?
CBODY67
You got me on that one! I forgot all about EPR vs ETR valves.
EPR, or Evaporator Pressure Regulator for standard A/C
ETR, or Evaporator Temperature Regulator for ATC
The only purpose of the two valves is to prevent the evaporator form getting too cold and icing up. The EPR accomplishes this by raising the low side pressure and the ETR valve cycles the compressor off if it gets too cold.
Here's the deal on them for the 21'st century:
Most of the EPR valves ever made are now shot and don't work anymore, with the exception of some that were in cars where the A/C was always serviced and kept alive. A few years ago I was helping a friend get the A/C up and running in his Challenger and his EPR valve was stuck. I ordered three NOS valves, one for him, and two to put in inventory, and they were all bad. The thermal wax inside them just doesn't last forever.
Most people will be converting to R134, and when doing so on an RV or RV-2 equipped mopar, step one is to yank out the EPR valve and chuck it in the trash. You then install a universal temp sensing switch on the evaporator that cycles the compressor when needed.
I haven't messed with any ETRs, but it's likely that most of them are worn out too, so the same steps would apply to R134 in an ATC system.
The clutch cycling modification will also work fine if one was to stick with R12.
Jeff