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1991 164L
27,582 Posts
Discussion Starter #1 (Edited)
Alfa 164 shop manual calls it an Evaporator Pressure Regulator Valve - "EPR Valve and it is located in compressor suction line, it maintains the fluid pressure at a minimum set value". The one in the USA 164 has a very small sensing tube that hooks to sensing tube on expansion valve which is in addition to capilliary tube on expansion valve that is clipped to same outlet port EDR valve tubing and valve are hooked to.

Now is it really almost the same valve by definition for a Pressure Operated Absolute (POA) valve or not?

Maybe maybe not as it seems like they both are in the evaporator outlet side going to compressor.

See this site for definitions of A/C parts: Auto A/C Terms - Glossary

Here as some definitions form that glossary:

Evaporator Pressure Regulator Valve - EPR Valve

"Early Chrysler Corporation A/C systems utilized EPR valves to maintain the proper refrigerant pressures in the evaporator. The ERP Valve was a device that regulated evaporator pressures creating a back pressure."

"Located in the rear suction port of the Chrysler RV-2 A/C Compressor, this system design has been replaced with more current designs using cycling clutch compressor and pressure sensing switches located in the low pressure lines of the A/C system."

[Now since Chrysler and Alfa were in cahoots when 164 came to states in 91 maybe we really do have an EPR valve set up. Since it is hooks to compressor suction port hose.]

I wonder what the difference as it also hooks to evaporator outlet, maybe the difference is the sensing tube [see definition below for External Equalizer] and extra sensing tube on expansion valve? Some Asian cars in same era had same expansion valve as one for Acura Integra fits USA 164.

Pilot Operated Absolute (POA) Valve

Like the suction valve, the POA valve is a suction throttling device that is located at the outlet of the A/C evaporator and is used to control the amount of compressor suction on the evaporator.

The POA valve was used on some General Motors and Ford air conditioning systems through the 1970�s. On these A/C systems, the compressor would run constantly whenever the A/C system was on. Under certain operating conditions, less compressor suction was required on the evaporator. The POA valve would then close off the flow of refrigerant, effectively reducing the amount of compressor suction.

Suction Throttling Valve (STV Valve)

Typically used on older A/C system designs, the STV valve has been replaced because of fixed orifice tubes and cycling compressors.

The STV Valve created a backpressure. It actually controls the amount of compressor suction on the evaporator. When liquid refrigerant (freon) enters the evaporator, it boils and changes state to vapor refrigerant. That vapor is �pulled� from the evaporator by the A/C compressor suction. If there is too much suction on the evaporator, the evaporator pressure and temperature will become too low, causing it to freeze the condensation from the hot air. If the compressor suction is too little, the evaporator pressure and temperature will not be low enough to maintain proper cooling performance in the vehicle.

The STV Valve or Suction Throttling Valve, located at the evaporator outlet, controls the amount of compressor suction and therefore refrigerant flow through the evaporator. - regulated device, used on some Ford and General Motors systems, that controls refrigerant flow to prevent evaporator core freeze-up".

Expansion Valve

Every automotive A/C system includes an expansion valve or expansion device of some sorts. The typical expansion valve, also referred to as a thermostatic expansion valve is... located at the inlet of the evaporator. The expansion valves function is to create just enough of a restriction in the A/C system so that hot, high pressure liquid refrigerant from the condenser can be reduced in pressure and temperature to become low temperature, low pressure liquid refrigerant before entering the evaporator.

Understand that refrigerant has a pressure temperature relationship. Whatever change you do to one will automatically effect the same change in the other. That means, just increasing the pressure of refrigerant will automatically increase the temperature of the refrigerant without adding any external heat source. The opposite is also true.

Therefore, in an automotive air conditioning system, it is very important that the liquid refrigerant entering the bottom of the evaporator be low pressure, cold refrigerant. As the refrigerant leaves the condenser, it is high temperature, high pressure refrigerant. By just restricting the flow of that refrigerant, it is changed from high pressure to low pressure refrigerant. Because of refrigerants pressure temperature relationship, when the pressure is reduced, the temperature is reduced automatically.

In operating within the auto A/C system, the expansion valve uses a temperature sensing bulb that is attached to the evaporator outlet and connected to the expansion valve on a capillary tube. That tube is a very thin tube that should never be kinked or bent. The temperature sensing bulb senses the evaporator outlet temperature and regulates the opening and closing of the expansion valve so that the evaporator always has an adequate amount of liquid refrigerant entering the bottom of the evaporator.

Other expansion valve designs like the H valve or block type expansion valves eliminate the capillary tube sensing bulb. That is because these types of valve attach to the evaporator in such a way that the cold vapor refrigerant leaving the evaporator passes back through the valve. The temperature sensing bulb in integral to the suction side of the expansion valve without the external capillary tube.

The expansion valve also creates one of the two divisions between high and low sides of the A/C system. The second division between high and low pressures is at the compressor, where compressor suction ends the low pressure side, and the compressor discharge, releasing compressed refrigerant to the condenser, is the start of the high pressure side of the A/C system.

External Equalizer

Some conventional type expansion valves which use a capillary tube sensing device, also include an external equalizer tube. The external equalizer is actually a thin capillary tube that is attached to the expansion valve and also threads into the suction line of the A/C system.

The external equalizer senses the suction line pressure returning to the compressor. In doing that, it provides a shock absorber type action for the expansion valve so that the expansion valve is not moving too quickly from fully opened to fully closed. In short, the equalizer moderates the expansion valves opening and closing.

Understand that external equalizer type expansion valves include two capillary tubes and are not interchangeable with other expansion valve designs that only incorporate one capillary tube.
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