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Hi,
I concur with Machine Man. The accumulator's low pressure switch may need to be replaced.
But before that, connect the AC gauges and see if the freeze-up/frosting occur BEFORE the low side pressure goes down to 29psi. If this happens it might indicate that the orifice tube is blocked/partially blocked which you must replace. Blocked expansion device could cause compressor damage by restricting refrigerant oil going to compressor.
Most low pressure switches' cut-off point had been "set" at the factory. If you get an adjustable switch you must use standard AC manifold gauges to set its cut-off point which is about 29psi for R134a.
The "set" value is important to be correct thus must be referenced to standard gauge. This is for achieving maximum cooling (when system is ok) plus for safety as to turn the system off in low refrigerant condition or during blocked expansion device (when system not ok).
How to test the switch?
On the car you could do this with switch still in its place AND you would need to connect AC gauges. With AC OFF the low side pressure would rise to above 60psi. Test the switch now with voltmeter set in lowest ohm reading. There should be continuity. If not the switch is defective. Then switch ON the AC. Watch the low side gauge until reading goes down to about 29psi and the compressor should be OFF. If not the switch is defective.
Regards,
Amarin.
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