Yes there is a low-pressure switch that acts like a 'circuit-breaker'
for the compressor. It is a 2-wire switch (Off/On type). Low pressure
in the line opens the switch and saves the compressor from working with
no refridgerant/oil charge. The switch usually located at the
accumulator, and can be bridged easy enough with jumper-wires. If the
compressor engages when the switch is bridged, most likely the switch if
faulty. You posted that the system is now fully-charged, so the switch
test is ok to do, just for testing purposes, it is not the 'fix'. The
switch isn't expensive and easy to replace. If bridging the switch
doesn't engage the clutch on the compressor, then either the clutch is
faulty and/or the compressor is.
There is a good reason why the refridgerant charge is low.....a leak. A
leak must be found and fixed....maybe a fitting loose enough to leak, a
bad compressor, or even a hole in the condenser. A leak usually also
means air/moisture has gotten into the system.....a bad thing. There
are leak-detector kits available at the parts-stores, but the system has
to be operating in order to use one. Check for any oily residue
in/on/around the compressor and all fittings in the lines. Oily residue
is the sign of a leak. If it turns out that the compressor is bad, then
the job is a matter of replacing parts. A rebuilt compressor isn't too
expensive. New oil must be installed in the compressor. A new
accumulator must be installed. The remainder of the oil charge goes into
the accumulator. Also install a new orfice tube. New O-rings should be
installed at all required places. If you can replace those parts
yourself; the system must then be put in a vacuum for at least one
hour or longer. If the vacuum 'holds', then the system can be
recharged. Either have a profession do this part(recommended) or rent a
vacuum pump, along with a manifold-gauge set, and DIY. If you are not
experienced in this procedure the smart thing is have it done by a
pro......it can be dangerous TO the inexperienced person!
Bottom-line here is find/fix a leak first, then deal with any faults in
Hope this helps some.....
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