Where is the ac low pressure switch located

The system has to make the low pressure limit switch before it energizes the system. If you have 12v at the low pressure switch and verify that there is enough refrigerant in the system to make the switch, try jumping out the switch. If the compressor energizes the coil you are looking at a bad switch. If the compressor clutch does not energize I would look to the AC relay or maybe a bad switch at the control head.

The low pressure switch is just a sense input to the PCM - powertrain control module > Grantit , it is needed for the PCM to know the pressure in the system . But the PCM must energize the compressor clutch relay for the compressor to engage . Finding the compressor clutch relay in the under hood fuse / relay box an testing there would be the best place to start . Pull the relay out of the fuse box , look on the bottom ! You should see four set's of number's ,30 & 87 plus 85 & 86 . 30 & 86 should have B+ voltage . Use a multi-meter to test . 85 goes to pin # 1 connector 3 at the PCM . The PCM supply's a ground here to energize the relay if condition's are right . You could jump pin's 30 & 87 an if the compressor clutch coil is good ,the compressor clutch will engage . Video's on youtube showing how to do these test .

Looks like the low pressure switch gets power from a 10amp ac fuse. Power then goes to the ac relay which is powered on by the ac heat controller on the dash. Power then goes thru the high pressure switch to the compressor. The ac relay is grounded to the body. Do you have power on the lite and dark green wires going into the relay and is it grounded ?

Have you tired jumping the AC compressor low pressure switch?

Put a jump wire in the high pressure switch plug. If the compressor works. replace the high pressure switch. Let me know and we can go from there.

yes, if you can figure out which terminal is what, you will be able to jump. Be carefull dont send 12v up the wrong wire or you will fry computer. I would pull relay out and jump at the compressor pigtail, its much safer, and the car dosn't need to be running, all your checking anyways is that the clutch is working which should give a click sound every time you tag 12volts.

Try checking the low pressure and high pressure switches. If one of these are faulty it can keep compressor from working. Take a paper clip and jump the ports on the plug in for the switches and see if the compressor comes on if it does then that switch is bad.

if you used a pressure washer ,you could have caused a leak ,if there is no freon the low pressure switch wont let the compressor turn on,even if you didnt use high pressure,engine degreaser may remove corrosion on the line set or the condenser ,also causing a leak, the high or low pressure switches may still be wet, follow the line set ,fat line (low pressure switch with a plug w/2 wires)unplug it make sure its not still wet inside,do the same to the high pressure switch on the small line,check the fuses ,pull the ac relay make sure there is no water underneath,and the prongs are dry,if the blower fan in the vechile isnt working on 2,3,or 4 speed it wont let the ac turn on,if all that checks out ,turn the fan on high max ac unplug the green wires or wire on the compressor right behind the belt pulley,check for 12v dc,if none,you lost a relay or one of the pressure switches,fuse,maybe broken wire,if 12 v. is there,your clutch coil fried on the compressor pulley,good luck, hope you figure it out

Check wires going into it from harness.. make sure there is no break.. If not have compressor checked at autozone or advanced auto.

The power to run the compressor clutch coil goes from the battery, to the AC Clutch Relay, somewere in the engine compartment fuse box, then it goes to the positive side of the AC compressor clutch coil; goes thru the coil, activating the compressor, and then goes to complete the circuit through another switch (high pressure protection switch) in the back of the AC compressor and finally reaching negative or Ground.

Disconnect the AC compressor clutch connector and using a 12 V bulb with 2 wires (test lamp) check the following:

1.- connect 1 lamp wire to battery neg; with the other check both pins at connector with the AC in the RUN (AC and ignition switch on ) you should have power in one side.

2.- connect 1 lamp wire to battery positive and with the other check both pins at connector, lamp should light getting the ground from the clutch connector thru the high pressure compressor switch to ground.

On the other side what makes the relay close and let the power flow to the clutch works with the low pressure switch, (if the freon pressure is too low it opens and kills the ground to the relay coil and that kills the compressor), that low pressure switch is in the low pressure side of the freon tubing, the fat pipe that comes from inside the firewall into the accumulator/dryer, a big aluminum cylinder sitting on the right side of the engine compartment in GM cars.

To know if the low press switch is the cause you can unplug it and connect both legs with a paper clip for a minute or two, no more, you don't want to damage the compressor. anyway if jumping the switch makes the compressor come alive and kick in, you either have low freon pressure or a bad switch; it's time for the pressure gauges and check how the compressor is pumping and that is better left to a pro.

By the way you said that your system is a R-12 system, have you considered switching to R-134a the new "ozone friendly" freon? to do that you need to evacuate the system with a recycling machine and pull vacuum in your AC, if it holds the vacuum for a while, then you can be sure that there are not leaks and then dump 1.5 or 2 pound (check the labels in the engine compartment) of R-134a into your system. it will be a good idea to put some fluorescent leak detecting dye in the system to check for leaks, just in case..