Yet another ac question

[dan juhasz]

After the overhaul of the hvac system on the 67 gtx I noticed that my high side ac readings are much lower than they should be or that I expected. 50 psi. System seems to be working. I replaced the drier, compressor, expansion valve, flushed and leak checked the condenser and evaporator. Only old piece that was reused as is , is the EPR valve that slides into the suction side of the compressor. It stands for evaporator pressure regulator, I don't know how it functions or if it is malfunctioning can it cause the low high side pressures. If not could I have gotten a dud reman compressor?

 

[Mike67]

Use a P&T chart to accurately charge, if its not getting to those pressures it could be mechanical, non condesables or a restriction.

 

[oldbee]

What's the low-side press(25-45)? Cud be the epr or stuck valve in comp.

 

[dan juhasz]

Low side is where I would expect 35 to 40 psi

 

[oldbee]

Just curious why an expansion valve&& an epr valve, maybe mike67 will chime in again.

 

[oldbee]

Ya know a normal low-side would still show with a low charge; how much did u put in( lbs,oz or cans)?

 

[dan juhasz]

Just curious why an expansion valve&& an epr valve, maybe mike67 will chime in again.

From what little I gather from reading the epr is like a cycling valve. I really don't understand it completely.

 

[dan juhasz]

I

Ya know a normal low-side would still show with a low charge; how much did u put in( lbs,oz or cans)?

I filled until I had a clear sight glass in the drier. At home I don't have a charging station, just brought home gauges and a 30 pounder of r12.

 

[RJRENTON]

Gentlemen,
The purpose of the expansion valve and EPR valve (evaporator pressure regulator) is:
Expansion valve meters the LIQUID refrigerant into the evaporator to maintain an even amount of refrigerant to achieve maximum cooling...evaporation rate....too little refrigerant results in luke cooi temp being discharged. Too much refrigerant results in poor cooling due to flooding the evaporator allowing no time for the refrigerant to boil and abdorb heat. Remrmber, you do not make cool but remove heat (thru the process of latent heat of vaporization...removal of heat).
The purpose of the EPR valve is to maintain a constant evaporator pressure, in the case of R12, 30 psi equals approximately 36 drgrees to prevent accumulated condensate on the air side of the evaporator from freezing.
The two valves work in conjunction to maximize cooling efficiency.
Different refrigerants (R12 & R134A) perform according to their individual specific heat and pressure characteristics and require different control methods...like GM's CCOT (cycling compressor clutch for pressure control and an orifice tube or expansion valve for liquid refrigerant control.
Thus endith the lesson....questions????
Bob Renton

 

[dan juhasz]

Gentlemen,
The purpose of the expansion valve and EPR valve (evaporator pressure regulator) is:
Expansion valve meters the LIQUID refrigerant into the evaporator to maintain an even amount of refrigerant to achieve maximum cooling...evaporation rate....too little refrigerant results in luke cooi temp being discharged. Too much refrigerant results in poor cooling due to flooding the evaporator allowing no time for the refrigerant to boil and abdorb heat. Remrmber, you do not make cool but remove heat (thru the process of latent heat of vaporization...removal of heat).
The purpose of the EPR valve is to maintain a constant evaporator pressure, in the case of R12, 30 psi equals approximately 36 drgrees to prevent accumulated condensate on the air side of the evaporator from freezing.
The two valves work in conjunction to maximize cooling efficiency.
Different refrigerants (R12 & R134A) perform according to their individual specific heat and pressure characteristics and require different control methods...like GM's CCOT (cycling compressor clutch for pressure control and an orifice tube or expansion valve for liquid refrigerant control.
Thus endith the lesson....questions????
Bob Renton

Back to my original question of a full charge r12, only old component is the epr, and my high side pressure only 50psi, can a defective epr cause this or do a have a dud reman compressor?

 

[RJRENTON]

Dan,
The possible ptoblem is a detective compressor valve or too much infernal leakage (blow by).
Discharge pressure is related to air entering the condenser...the higher the temperature, the higher the pressure. I never measured the discharge pressure only the suction pressure. With with a correctly functioning EPR valve should be in the 30-40 psi range and discharge pressures in 150-200 psi range with 90 degree air entering the condenser. I just charged to a clear sight glass plus approx 1/2# additional refrigerant.
Bob Renton

 

[dan juhasz]

Dan,
The possible ptoblem is a detective compressor valve or too much infernal leakage (blow by).
Discharge pressure is related to air entering the condenser...the higher the temperature, the higher the pressure. I never measured the discharge pressure only the suction pressure. With with a correctly functioning EPR valve should be in the 30-40 psi range and discharge pressures in 150-200 psi range with 90 degree air entering the condenser. I just charged to a clear sight glass plus approx 1/2# additional refrigerant.
Bob Renton

Thanks, for the schooling. So the epr is ok, and the reman compressor must have a fault.

 

[oldbee]

Slow up a minute- all I heard you say was gauges& freon brought home. Did u vacuum system first?

 

[dan juhasz]

Slow up a minute- all I heard you say was gauges& freon brought home. Did u vacuum system first?

Yes I have a air vac at home, small but pulls a strong 29 inches of mercury, and I let it run for an extended period as the system was done for a decade.

 

[JimKueneman]

When switching to 134, per Classic Air recommendations, I left the EPR valve out. I can get too cold in 105F desert weather with it.