Different versions of RV2 compressors

[TBass]

So my original '66 compressor seized up a few years back and threw my belts off, I am guessing I am not the first to have that experience. I was given a rebuilt compressor from a guy who said he removed it from a '66 Coronet and it was running. The compressor seems to be functional and healthy as far as I can tell at this point, so I removed the brackets and cleaned it up to prepare it fir install on my 383 Charger brackets. My original compressor had a different type clutch assembly and used three long bolts to mount up to the beefy cast iron bracket that bolts up to the cylinder heads of the engine whereas the replacement compressor only has two bolts. I swapped over the good clutch form my original compressor since it was still in good functioning order as well. The compressor bolts up fine with just the two bolts and there really is no issues there. It is mounted on the car and good to go. However, I had to swap the inlet from the back of the compressor at the top and there is where I see a significant difference. (I am not super sharp on A/C since my mechanic experience comes mostly from race cars and aircraft. So this is all fairly new to me.) My original setup uses the big 3/4" copper tube that runs out of the compressor and around the back of the engine and this replacement setup was all rubber hose from that side. It appears that my original compressor has some kind of internal differences from my replacement one. Is there anyone here who can provide me some insight to these differences? Can I continue with this swap or should I search for an exact replacement for my original?

 

[Slantsixdan]

There are two different sizes of this compressor. The V2 is 9.45 cubic inches, and the RV2 is 10.5 cubic inches. There were also differences in cylinder head and oil pan configuration.

I am guessing that when you say "it appears my original compressor has internal differences from my replacement one", you mean when you removed the inlet fittings from the rear of the compressors, you saw something different inside the new vs. old compressor. The device installed in the hole in the compressor, covered up by the inlet fitting, is called the EPR valve. Evaporator Pressure Regulator. It is present in all compressors except those used with dealer add-on (under-dash) air and on factory A-body systems prior to 1974; instead of an EPR valve those systems use a thermostatic clutch cycling switch to engage and disengage the compressor to prevent the evaporator freezing up. If your one compressor did and the other compressor didn't have an EPR valve installed, that would cause an apparent difference when you remove the inlet fittings.

There have been several different designs of EPR valve over the years, so it's also possible to see something different in that location in the two compressors even if both have an EPR valve.

You must have either a working and unclogged EPR valve or a working thermostatic clutch cycling switch. One or the other, not both. If you don't, the system won't cool correctly and the evaporator will freeze up.

Don't worry about the configuration of lines (rubber vs. metal, etc).

 

[TBass]

So can I swap the EPR stuff out for my thermostatic piece? Would I be better off getting a new compressor? I was gonna say my original had some kind of elements or something in that port that led me to believe it had something to do with temps but wasn't exactly sure how to word that.

 

[Slantsixdan]

What is your "thermostatic piece"?

 

[TBass]

These are pics of what I am working with. The one with bolts in the housing is my original compressor. The other is my replacement. Can this EPR stuff be swapped?

 

[Slantsixdan]

That's two different types of EPR valve. Yes, they're interchangeable; see pics of all three types here. But they're also fault-prone and capable of causing aggravating problems big and small if they're not in good condition; if you're using R12 refrigerant and you are bound and determined to keep the system in its original configuration, you should seriously consider installing a new one (same page as what I just linked). If you're going to R134a refrigerant, or you are staying with R12 but don't necessarily require the system to be exactly as originally shipped, remove the EPR valve altogether and install a thermostatic clutch cycling switch instead, per discussion here and here. Options in clutch cycling switches are discussed here (sorry, pics no longer load -- I'll try to fix that next week)