Marqoid

I have a 1994 4.0 Ranger. The A/C had always been okay (not cold) until about 18 months ago. I tried to fill it with new coolant and noticed something unusual. With a pressure gauge connected and the a/c running the compressor will run and increase the pressure in the system to the red line on my gauge (unsafe), but then it will immediately click off and the pressure will drop to zero. It seems that the compressor is working fine, it just can't maintain the proper pressure, is there a pressure switch that controls this? Please help; I'm in Arizona and need some A/C.
Thanks

Shadow

Sounds more like the expansion valve is clogged. That would allow the compressor to build to maximum pressure without the system delivering cool air. If the pressure is dropping to 0, check it thoroughly for leaks on the high and low pressure sides, completely evacuate the system (this will dictate paying someone or renting some equipment if you know how to do it), and be sure it's using the right refridgerant.

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The Shadow