Back 20 years ago, in the old ACKits.com forum (which was run by a/c professionals in Arizona), it was confirmed that the Chrysler EPR item, as well as the GM POA Valves ARE ADJUSTABLE !!! They were NOT built to "a spec" and suspected they would have the correct regulation capabilities to work with R12 gas, they HAD to be adjusted on their own little assembly line to function correctly!
For warranty purposes, GM never did mention this, as they wanted to see if the supplier was building the POA valves as they should have been, to not cause problems. So they said "replace" rather than "adjust". The other thing was that GM would only pay for a repair ONCE, so they did not want to pay one dealer to adjust and then use the same labor op at another dealership (or repeat service visit to the same dealership) to later replace it.
FORD, on the other hand, had a procedure in their factory service manuals, after they went to the GM POA valve in the middle 1970s, had a procedure to use to ADJUST them!!! Of course, to do these checks at the Ford/Lincoln-Mercury dealerships, the POA had to be removed from the car.
Back to the old 2003-era postings in the
www.ackits.com forums, it seems that EVERY factory a/c system has had adjustability built into it, although the OEMs might not have ever mentioned it, but the valves had to have had some way to calibrate them when the valve mechanisms were built -- period. Common sense?
So in the case of the Chrysler EPR items, they are adjustable too. Just turn the adjustment screw abt 3/4 turn CCW and reinstall. With this small change, the pressure differentials between the high and low come back into approximately the same relationship as with the prior R12 relationship . . . but with R134a. With, of course, the reduced-charge level for R134a.
It was also mentioned that the same thing worked with all versions of the GM systems. Hot gas by-pass, POA, and VIR (with a mini POA valve in it). Which goes back into the later 1950s. ALL items were adjustable, even if such adjustments were not mentioned in the factory service literature.
When I mentioned this adjustability capability in this forum, about 15 years ago, there was one poster who said adjusting the EPR was not needed as the expansion valve would compensate. Yet a parts acquaintance (whom I conversed with during the change-over to R134a, that then worked for Four Seasons) said they were considering doing a line of R134a expansion valves, but this never happened, or I read of such. BTAIM
The reason I started to investigate the R134a change-over things is that we were having GM customers (at the dealership) that wanted/needed to get their R12 systems converted to R134a. Plus some issues with concours judging at national Buick Club meets, as the participants with factory a/c cars wanted approval to do the "POA Eliminator Kit" installation (which was very home-made looking, to me) and used a machined brass block to install cycling switch items in it. So my investigation began.
I ALSO discovered that in the 1977 model year at GM, which used the Cycling Compressor Orifice Tube (CCOT) system, that the cycling switch was adjustable, too! When I found this, it turned out that my '77 Camaro had such a switch on it! Turning the small adjustment screw about 1 turn CCW for that one, with the gas charge that worked with R134a (usually about 90% of the R12 charge).
After all of this, another issue emerged . . . age of components. Namely the regulating items. Allegedly, the rubber inside of them would age and fail when the adjustments were made. New replacements long gone.
Back in about 1975, I happened upon a new 1975 Plymouth Valiant with factory a/c being converted to a "Chrysler-level" a/c system by the installation of an EPR valve into the a/c system at the line fitting at the compressor. Pretty simple. Unplug the cycling switch and install the EPR valve so the compressor did not cycle.
Sorry for the length, so far! Back to the original issue.
If the a/c condenser is "freezing up", which would also mean NO airflow through the dash vents, that should not be happening with an R12-regulated system with R134a gas in it! Reason is that the system performance should be a bit less cold than with R12, in the first place. What you are probably seeing is normal condensate production, not "freezing up".
My experiences and observations are that the main culprit is the retention style of the two halves of the a/c cars, combined with a stiffer rubber gasket, lead to the leaks. If you place the new gasket against the two case halves, where it seals, all looks pretty good. BUT when you slide the clip/nuts over the side they slide onto, THEN put the gasket against that, it is easy to see that little gaps will exist at EVERY retained clip where the gasket touches them, on EACH side of the clip! When the bolts are torqued to specs, the gaps can become smaller, but are still there AND they will leak, eventually.
The leaks/seeps are unknown for a long time, until you take out the rubber floormats from the carpet. THEN you'll discover dampness and wonder where it came from! It is made worse by the thick vinyl OEM floor mats Chrysler used, too. No way for the moisture to escape. THIS is how I discovered the situation with the gasket/seal/retention issues on my '70 Monaco DH43 after I bought it used, in about 1975. My parents had already had a/c case leak issues with their 1972 Newport Royal by that time, which did not work (when I initially examined the lower hvac case area on that car). I had also been at the local dealership when a customer had complained to the dealer principal about a "failed repair" on her 1969 Fury, for a/c case leaks.
To me, the best thing to do would be to get rid of the "time saving" push-on clip-nuts and replace them with individual square nuts (the larger OD the better, but square rather than round). THEN, the factory-type case gasket should work much better, I suspect.
To recap, with the EPR valve adjusted (as above), the a/c vent temps should get back to the old R12 spec of 40*F orientation. With R134a, they will be higher a bit with a non-adjusted EPR valve. Whether the compressor is converted to cycle or not.
The issues with condensate production is normal, but with age and such, the retention method Chrysler used for the halves of the hvac case is a real issue, plus that (as the old-line Chrysler service manger mentioned, they deleted the "drain pan" in Fuselage cars' hvac cases.
My apologies for the length. Thanks for your time! These are MY observations and experiences with two things. Chrysler factory a/c R12 systems converted to R134a. How the factory a/c cases on Fuselage cars are sealed and held together.
Take care,
CBODY67
