I’ve been troubleshooting my AC system and suspect that I have a bad EPR valve. This is for a stock (1970) system running R12 that has new hoses, new dryer, new expansion valve, rebuilt RV2 and original EPR valve (which I suspect is stuck closed). I re-used my condenser and evaporator (both flushed with AC flush solution). System held good vacuum before being charged. However, running pressures suggest the EPR valve is stuck closed.

I’ve found a number of NOS EPR valves and have one on the way. My concern is EPR valves have been obsolete for a long time, so my NOS valve likely has been sitting on the shelf for years. Replacement EPR valves were covered in a protective coating that by today (from what I understand) has become a sticky glue-like substance. I plan to soak the EPR valve in mineral oil in the hope that it will remove/release the coating.

So this leads me to my question. Is there any way to test the EPR valve before it goes back in the system? The service manual implies these things are delicate so I am not sure what I can do to test it out of the system. For obvious reasons I really don’t want to go through all this work just to find out the replacement EPR valve is also bad/stuck.

Also, I realize that instead of using an EPR valve I can install a thermal switch to cycle the compressor, but I prefer to keep the system stock (if possible). But if there is no way to confirm operation of the NOS EPR valve prior to install I may just bite the bullet and go that route.

Thanks!

Got an answer to my question on another forum, which I pasted below in case someone else is looking for this down the road.

If you remove the suction line and you can see the capillary sticking out the end of the valve, it is the thermally controlled wax valve. These were considered an expendable item and I do not know of any test procedure except with the unit installed as specified in the FSM. The inner section on this type valve is pushed down to open the ports, if it is closed a room temp, it is probably dead.

Did you find any info about how to clean an NOS one.I'm installing one in my car and was looking for what to use to clean it.

Nothing specific. Since mineral oil is used in R12 systems, I plan on soaking it in that to see how it works.

Just curious - is your valve open at room temperature?