In “Model Specific Discussions > MK1 Focus”, in the thread named “Bypass low pressure switch? “ austinpetemo asked “Where is the low pressure switch for the ac?” In answer, elsolo said “It's low on the firewall, next to the pass side strut tower, behind the PS reservoir.”
Looking in that area I found what I think is the low pressure switch (see photo below). Should I be looking somewhere under the fender?
Either way, can you direct me to a photo or engineering drawing of the connector with directions on where to press to unplug the wires so I can determine if the switch is open or closed?
I’m no stranger to automotive AC. I have gauges for both R12 and R134a, a vacuum pump and a “can heater”.
When the engine is cold and not running, the refrigerant pressure will be equal through out most AC systems. Under those conditions I get 50 psi on the easily accessible HI pressure side. I don’t know if 50 psi will close the low pressure switch. I suppose not since the compressor clutch does not engage when the AC is turned on with the engine running. If the switch is open, I want to monitor it while adding refrigerant to the low pressure side with the engine off. Once I see the switch close I can start the engine, get the compressor running and add refrigerant as required. This way the compressor will not be compromised by being forced to run with insufficient refrigerant.
After charging I can look for leaks. However, if the system has not been serviced at all in 13 years then it is possible that it’s current condition is just due to “normal/expected” refrigerant losses.
I realize that there are other things that could cause the compressor clutch to not function but, having found that there is insufficient refrigerant I want to “fix” that first.