My a/c is inoperative, clutch will not engage in normal operation. i am t getting two codes p1540 refrigerant overpressure/ac compressor disabled and u1000 class 2 communication malfunction. i have already the refrigerant pressure checked and it is fine. i found a 12v 2-wire connector unplugged which is hot all the time wires are blue/white stripe and black mounted to firewall behind the engine right behind where the air filter goes looks like it was it was mount in another place because it has another ******** it and it leads back into car on drivers side via a bigger tube with wires in it. where could this go? the only thing that is not work in the car is a/c. both fans still work

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.

The Trainer 40 When the compressor won compress

If all you get is hot air there are several possibilities. The compressor is driven by the serpentine belt and is engaged and disengaged by an electric clutch mounted on the compressor drive pulley. With the engine running, have an assistant turn on the AC while you observe the AC compressor clutch. If the clutch engages, you can be reasonably sure that the system has freon, and the electric circuit is OK. If the clutch doesn't engage, which is the most likely situation, either you are low on freon, the AC clutch relay is inop, or AC compressor fuse is open (blown). A search of Google images will give you the location of the AC relay. You can pull out the relay, carefully remove the cover, reinsert the relay, and engage the compressor clutch by manually closing the relay contacts. Warning: do this only for a second or two in order to see the clutch engage. If the clutch does engage, then you are probably low on freon. There is a safety switch that prevents the clutch from operating if there is not enough freon in the system. Hopefully, this is the case. Go to Walmart and get two cans of r-134 and the inexpensive kit, and following their instructions, charge your system. If this is not the problem, you'll need a set of AC gauges and the skill to use them. Hope this helps. Dano

Find the AC compressor. The pulley on it has an electric clutch that allows the compressor to run when the AC is on and not when it is off. With the engine running you should be able to see if the clutch is turning or not. The pulley turns all the time the engine is running only the clutch behind the pulley starts and stops. Look at the pulley with the AC off. Have someone turn it on and see if the clutch engages to turn the compressor. If it doesn't engage there are a couple thing that could be wrong. First the clutch has burned out and no longer works. The fuse on the AC clutch is blown. Check the fuse. More likely, if the cold air has been getting warmer, the AC system has a refrigerant leak. The system has a low pressure switch that prevents the clutch from engaging when the refrigerant pressure is too low. If the fuse is good then you need to have a qualified AC Technician check the system.

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Gaker

Locate wires coming from compressor clutch and trace to nearest plug that you can unplug. Turn on A/C to max cooling. If clutch not engaged (center of compressor drive pulley not spinning with pulley), unplug compressor clutch wires and use multimeter to check voltage going to compressor clutch. If voltage is around 12 volts or more, then clutch should be engaged when plugged in. Plug clutch wires back in (with motor still running and ac set to max). If clutch still not engaged, then clutch definitely bad because 12V signal should engage it.

I would check the following possibilities:
1. Is compressor clutch working? - You need to do this when the ac is blowing hot air only - locate compressor drive pulley on engine - rubber belt wraps around it. Start engine and set to max ac. When the ac is blowing hot air, look at the center of the compressor drive pulley using a good flash light - watch it for a while, it should be spinning with the pulley - this means the compressor is engaged. If not, the compressor is not engaged. If your ac is blowing hot air, then the compressor should be engaged and running (trying to cool). If it is not engaged, then your compressor clutch is probably going out. Could be low voltage to clutch, but more likely the clutch is worn out and only working some of the time. Note: if working normally, the compressor clutch will engage and disengage in cycles- but the air should always be cold. If clutch is bad, compressor would need to be replaced (sold as one unit). This is tricky to diagnose and could take some time - you need to do it when ac is blowing hot air but set to max cooling.

2. Low on refrigerant or refrigerant has moisture in it? If your ac blows cold initially after being off for a while, then heats up, and continues to regularly cycle back and forth between hot and cool air, then the system may be low on refrigerant or the refrigerant may have moisture in it that is freezing and restricting refrigerant flow. An a/c shop can check refrigerant level and even replace refrigerant if moisture is suspected.

Could be other issues, but I would start with these.

Good luck

Load placed on the engine takes place when the Compressor clutch engages. It will not engage if the system charge is too low on freon. It needs to be checked with a gauge, I think that may be your problem.

if the freon pressure is too high or too low there are two seperate pressure sensors that will disable the a/c clutch to prevent dammage to the compressor. You need to check (or have it checked, dangerous if you do not know how) the pressure on the high and low ports while you have you jumper wire in place and the a/c is running. PLEASE RATE MY solution as I am new on here, Thanks

scott it sounds like you might have a small leak. most a/c units will not engage the compressor clutch if there is no refrigerant. I would goto autozone and use a leak detention kit before I would do anything. Normally when you fill it up then you will hear the clutch engage... let us know

if refrigerating system low in presure(low refrigerator level)presure sensor wil not send signal to engage clutch...the second think if system under normal pressure check electrical connectors if they ok,a/c compressor is faulty.