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Originally Posted by HotRodr56
1994 C3500 454 EFI R134a system. The air quit working so I assumed low refrigerant. I bypassed the low pressure switch on the dryer but could not get the compressor to start. I discovered a pressure switch on the back of the rotary compressor and when I bypassed it the system ran but didn't cool very well. I checked pressures, ambient temp about 90 F. high side about 245 low side about 40. I thought this was a little low and since the system wasn't working without bypassing the switch I added almost a full can of refrigerant without much change in pressure. Second reading about 270 high side and still about 40 low side. The system will still only work with the switch bypassed and still does not cool very well. Could I possibly have a partially blocked orfice tube? Do these pressures seem to be in the right range? What exactly is the switch on the compressor for? Any ideas why the system doesnt put out cooler air? I am going out now to run a test with a thermometer in the vent to give me an idea of air temps. Any ides, suggestions would be appreciated.
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The switch on the back of your compressor is a high pressure switch, it is designed to turn off the compressor if pressures get too high to prevent damage to compressor or ac system. The pressures you mentioned sound high to me for only being 90 degrees out. I would think the pressures should be around 200 and 35 or so. If the system is overcharged it won't cool properly because the freon can't turn from a liquid to a gas and absorb heat readily. If the orifice tube was blocked you would see the low side drop very low. To me it sounds like your ac system is overcharged. The best thing to do would be to have the system evacuated and then charged with the proper amount at an ac service center. If your vehicle is equipped with an auxillary fan and the fan is not working, that will also cause your pressures to be too high and your ac will stop, i would probably check that first. Good luck!
06-26-2005, 11:23 AM
