Engine Size: 1.9L TDI
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 17
Pressure High: 160
Country of Origin: United States
Because of a worn out compressor, I replaced everything in the system except the evaporator and the liquid line with all new parts (including the condenser). Flushed using non solvent flush and dried with fresh air for 15 minutes. I've put in the proper amount of oil, and using a recycle machine, vacuumed for 50 minutes and put in the proper weight of charge. When driving at highway speeds the car will put out 23 degree air until the evaporator starts to freeze thereby providing low air flow. Just for background information, this system was doing the same thing last year before the compressor was determined to be wore out (hi and low pressures were starting to approach each other). When replacing the expansion valve, I noticed that it was a block with no capillary tube or electric plug on it. I haven't been able to find out what controls the compressor to stop the evaporator from freezing. There is a hi/lo pressure switch in the engine compartment that shuts off the compressor during overly hi pressure or lo pressure due to lack of freon. I've already replaced this switch. Since the expansion valve is in the engine compartment, I've made sure that insulating cover is installed over it. I'm thinking there should be something in the evaporator box that controls this, but I haven't seen anything clear cut by briefly looking at the description and operation on alldata at a friends house. Thanks in advance for anyones help.
This is a variable compressor system. The compressor has (or had) an internal control system which senses the low side pressure and reduces the displacement (becomes a less powerful compressor) to prevent the evaporator from freezing. The car has no other controls for evaporator temperature. It's built into the compressor.
It appears that your new compressor is defective in this regard. Observing the low side pressure, it should regulate itself to no less than about 20 psi even with the interior fan on low and the engine revved up. If the compressor does not reduce displacement and the low side is driven below 20 psi, this causes the R-134a to start to boil at a temperature lower than 32 F and the evaporator will freeze.
With the information provided. I would suspect as mk378 suggested a compressor or control valve issue. That is if the system is correctly charged with refrigerant.
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