RV2 cycling question

[70runner]

Followup to earlier post about A/C wiring on 69 Charger. Installed the correct 3 wire A/C switch, had the OE system evacuated and charged with R12. Working great, however, AC guy was worried the compressor wasn't cycling, could lead to evaporator freezing. AC guys, doesn't the RV2 clutch engage whenever the A/C or Max A/C pushbuttons are selected? Evaporator is protected by the EPR valve, correct? Is there a method to test the EPR valve function?

 

[1 Wild R/T]

Followup to earlier post about A/C wiring on 69 Charger. Installed the correct 3 wire A/C switch, had the OE system evacuated and charged with R12. Working great, however, AC guy was worried the compressor wasn't cycling, could lead to evaporator freezing. AC guys, doesn't the RV2 clutch engage whenever the A/C or Max A/C pushbuttons are selected? Evaporator is protected by the EPR valve, correct? Is there a method to test the EPR valve function?

Systems with expansion valves don't cycle... They control evaporator temp/pressure by varying the freon flow through the evaporator... EPR allows the system to work more effectively in spite of being undercharged....

 

[Nxcoupe]

^What he said. That clutch is not designed to cycle. Your ac guy should know this stuff.

 

[Some Car Guy]

Does the ac guy have gray hair?

 

[1 Wild R/T]

Does the ac guy have gray hair?

Probably not...

 

[70runner]

To his defense, really nice guy, some grey hair like me, but mostly older GM experience. Had a custom 57 Impala in the bay when I arrived. Was fine with using R12. Hard to find an AC shop around here with RV2 experience. Anyway, I didn't know enough about the RV2-EPR design at the time to address his concern. Back to my last question...

Anyone know of a method the test EPR function?

 

[Nxcoupe]

To his defense, really nice guy, some grey hair like me, but mostly older GM experience. Had a custom 57 Impala in the bay when I arrived. Was fine with using R12. Hard to find an AC shop around here with RV2 experience. Anyway, I didn't know enough about the RV2-EPR design at the time to address his concern. Back to my last question...

Anyone know of a method the test EPR function?

Is your ac blowing cold? Then it's probably working fine. Would have to watch gauges and if you have an old shop manual it probably tells you the function and testing in it.

 

[RJRENTON]

Is your ac blowing cold? Then it's probably working fine. Would have to watch gauges and if you have an old shop manual it probably tells you the function and testing in it.

The EPR valve (Evaporator Pressure Regulator) valve on the Chrysler RV2 Compressor system was designed, along with the Thermostatic Expansion valve (TXV) to maintain approximately 35 psi Evaporator suction pressure (and temperature) to prevent icing during high humidity conditions and low cooling loads. The TXV controls refrigerant flow into the Evaporator and a given percentage of superheat, while the EPR tries to maintain a given PRESSURE (~35 psi) by throttling the suction pressure at high engine RPM (cruise conditions). The combination of the TXV and EPR valves maintains a reasonably constant EVAPORATOR temperature and pressure (including superheat) to provide maximum cooling with a minimum chance of icing on the Evaporator air side. The system was designed to operate on R12. A switch to R134A REFRIGERANT USUALLY requires the REMOVAL OF THE EPR VALVE due to specific heat characteristics of R134A when using the RV2 Compressor. This is radically different than the later GM's CCOT (Cycling Clutch Orifice Tube) control system, which cycles the Compressor clutch to maintain approximately 38-40 degrees F Evaporator pressure.........
BOB RENTON

 

[70runner]

^Thx Bob. Pretty sure the AC shop was looking for the GM CCOT, cycling compressor. The Charger AC is working great, so I'll assume the EPR/TXV handshake is working properly.