QuestionQUESTION: The a/c motor does not turn. Where is the low pressure switch. I need to know how to get the compressor to start turning so I can try to fill the a/c with R-134.
ANSWER: Stan,
What type of vehicle are we talking about here. Different manufacturers put the low pressure switch in different places and even different models within the same manufacturer.
I will tell you how to locate it though. If you know where your low pressure port is, which I assume you do because you have already researched charging it. Trace that line in both directions. Towards the firewall and towards the compressor. Your switch will be directly installed into this low side line at some point. It may be on a hard portion of the line itself, or it may be on your accumulator if your vehicle has one. Your accumulator is an aluminum canister that is rounghly the girth of a soda can and has two hard lines coming from the top of it.
Once you find your switch, simply unplug the harness and with an insulated wire jump the connectors inside the harness. This will allow your clutch coil to stay energized while you are charging it (providing your a/c switch is on.
I hope I was of a little help. If you need anything more, do not hesitate to ask. Thank you for the question and good luck.
---------- FOLLOW-UP ----------
QUESTION: The veh. is a 1995 Buick Riveria,
I jumped the connectors and nothing happened.
Where would be the next spot to check for an open circuit.
How do you check the compressor itself.
AnswerStan,
The first check should be the fuse. Check the one labeled A/C clutch.
If this is good... you will need a multimeter for my checks from this point.
But first. You asked the easiest way to check the compressor. Run a hot wire from your battery and touch it to the power inlet wire on the compressor. If you have a two wire compressor run a good ground to the compressor ground wire. Typically... not saying yours is the same, but the ground wire is black and the hot wire is green. With a good ground, as you touch the hot terminal of the compressor with the wire you ran straight to the battery, you should hear your clutch engage. Naturally you will do all of this with the engine off.
Ok... stepping back into the voltage checks. With the key on and the A/C on check your compressor plug for 12v. If you read 12v and the clutch is not engaging... check your ground wire. It may be loose or have built up corrosion that needs to be cleaned. If you do not read 12V here... Locate your high pressure switch (on your high side line) and check this plug for 12V. If you read 12V on one side, use a jumper wire and jump this switch. you should hear your clutch engage. If it does... replace your high pressure switch, it is normally in the closed position and by not sending voltage forward, yours seems to be stuck open. If you do not read 12 volts at the high pressure switch... plug the harness back in and do a voltage check at the low pressure switch. With 12V on one side, if you jump it you should hear your clutch engage. No 12V? Our next step is the compressor clutch relay. Unplug your relay from the box. Check the coil for continuity. You should have continuity. Now check the relay box for 12 volts on the terminal that brings power to your coil. If you have 12 volts there, replace your relay. If you do not... the next step is your thermostat. This is usually mounted directly on the evaporator inside the cab. It will have a bulb that slips into the fins on your evaporator, or mounts to the fins of the evaporator. You should have 12 volts at on of the terminals on it. If you have 12 V, check the thermaostat terminals for continuity. You should read continuity. If you do not, replace your thermostat.
This is the basic run-down. If you need more specifics, just let me know. I believe, just going on the typicals... you will find your relay to be bad, your fuse to be blow, or a bad ground on your compressor. These are the usual problems. AND... just a footnote... if you read 12V on your low pressure switch, jump it and the clutch doesn't engage, this does not necessarily mean that your switch is bad. Your charge may be so low, it is not allowing the contacts to close.
Thank you for the question, and as I said, if I can do more, please let me know. Good luck.
