94 S10 2.2 I'm not getting power to the AC Compressor. Checked fuses and low pressure switch. Still no power. I can come straight from the battery and it will work. Any help appreciated. Thanks

In a 1994 Chevy K1500, the compressor should receive power when the AC button is turned on, assuming that the system is adequately pressurized and there are no other issues preventing it from engaging. Here are some steps to diagnose the issue:

1. Check Refrigerant Levels: Low refrigerant levels can prevent the AC compressor from engaging. If your system is low on refrigerant, it may need to be recharged. This is typically a job for a qualified technician.
2. Check for Refrigerant Leaks: If your system is low on refrigerant, it's essential to check for leaks. A leak can cause the refrigerant to escape and prevent the compressor from engaging. Look for signs of oil or refrigerant leaks around the AC components.
3. Fuse and Relay Inspection: Ensure that the AC system's fuse and relay are functioning correctly. You can consult your vehicle's owner's manual or a fuse box diagram to locate the relevant fuses and relays. Replace any blown fuses or faulty relays.
4. Check the Pressure Switch: Many vehicles have a high-pressure and low-pressure switch in the AC system. These switches monitor the pressure in the system and can prevent the compressor from engaging if the pressure is too high or too low. Check these switches for proper operation and continuity.
5. Inspect Wiring and Connectors: Examine the wiring and connectors leading to the AC compressor. Look for damaged wires, loose connections, or corrosion. Ensure that there is no damage to the wiring harness.
6. AC Clutch and Compressor: If all the electrical components are working correctly, you may need to inspect the AC clutch and compressor itself. The AC clutch should engage and disengage when the AC is turned on and off. If the clutch isn't engaging, it may be faulty, or there could be an issue with the compressor itself.
7. Refrigerant Pressure Sensors: Some vehicles are equipped with refrigerant pressure sensors that can prevent the compressor from engaging if the pressure is out of the specified range. Check if your vehicle has such sensors and test them if necessary.
8. Professional Diagnosis: If you've checked all of the above and cannot identify the issue, or if you're uncomfortable working on AC systems, it's recommended to consult a qualified automotive technician or AC specialist for a thorough diagnosis and repair.

Remember to prioritize safety when working on your vehicle's AC system, as it involves high-pressure refrigerant and electrical components. If you're not experienced in automotive AC repairs, it's best to seek professional assistance to avoid injury or damage to your vehicle.

Could be several problems. Depending on what vehicle you have you may have high and low pressure switches. If the freon is low, the low pressure will not let the compressor engage. The ac controller could be bad not sending current to the AC clutch. If you have power to the relay, depending on the vehicle, the relay may not be getting a ground signal.

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 ?

You did not say you had check the Freon level or the low pressure switch on the dryer. The low pressure switch will shut down the compressor when it is low on Freon. Hope this helps.

Some possible causes are the system is low on freon, a faulty compressor clutch, faulty low pressure switch, relay, fuse, or control switch.
Do you have power at the fuse and the relay ?

check your low pressure switch , and do you have gas in a/c unit if low it will not cycle on because a/c system don't have enough pressure to pressure switch to send signal to pcm were it will send signal to relay to cut on a/c compressor. If i can help further just re post.

Some nissans the AC lamp is tied to FUNCTION not FUSE. The lamp is on when the car engages the system and sends power to the compressor. On some the AC lamp will go off if your AC has leaked out and the low pressure safety disengagement has prevented compressor from being powered. Check pressures or check pressure switches.

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..

try removing the plug off the low pressure switch on the accumalator plug a paper clip into the plug and turn ac on if it comes on then your low pressure switch is bad or your low on refigerant.

If there is no gas in the system it as you pointed out the low pressure switch will shut the power to the clutch in the compressor off. your pressureswitch should be located near the dryer at the front of your Benz. You could try and bridge it to see if the compressor engages, how ever DO NOT try and keep it engaged without gas in the system or you may find yourself having to change the compressor again.