AC Compressor not engaging on 2000 Chevy Impala. Fuses and AC relay okay. No power at compressor. Need wiring diagram. Also need to know if compressor requires 12v for operation. If not what should voltage read?

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.

According to the wiring diagram, fuse 10 (AC compressor relay) is powered from "hot at all times" bus in the fuse panel.

Check fuse contacts in the fuse block.

It might be an in-line fuse or the switch itself

What is year--make--model? Can't look up diagrams w/o that info. Did you check fuses and or relay? Any applicable trouble codes? If two wire connector at compressor, that should be voltage and ground. For testing you might be able to run jumper wires to proper terminals at compressor from battery to see if compressor clutch will engage, engine running. Don't do it very long, W/o out more info about the vehicle, not sure how to go any further. Just my opinion.

Can you tell if compressor clutch is engaged? If clutch isn't engaged only the belt pulley will be moving and the compressor clutch is not engaged. If not engaged, no ac.

Can you check for applicable hvac codes? To check codes, your-self, at the least, you need an obd2 code reader, that will check manufacturer specific codes as well as po.

I haven't looked at your wiring, you could probably check voltage and ground for compressor, hvac on.
In the diagram, you see applicable fuses--clutch relay-- the top wire at ac clutch is voltage--black wire is ground.

Please first check the fuse, if it's okay, have the refrigerant checked by an A/C specialist.

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 ?

The only thing it could be is the conrtol wire of the A/C compressor clutch relay is shorted to one of the wires grounding at the alternator . The PCM - engine computer controls the grounding for the A/C compressor clutch relay. Find the A/C compressor clutch relay in the under hood fuse box , pull the relay out of the fuse box an look on the bottom . You will see four sets of numbers . 30 & 87 plus 85 & 86 . Take an ohm meter an check pin 85 to ground with the ground wire's behide the alternator connected , you will have continuity . Disconnect the ground behind the alternator an you will probably have a open circuit . When the motor was changed wire's were pinched or something . Most likely . Here , check out the wiring diagram http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model an engine size . Under system click on HVAC , then under subsystem click on HVAC controls . Click the search button ,then the blue link . Fourth diagram down is for the A/C compressor clutch relay circuit. Don't know if know how a computer controlled relay circuit work's . Looking at the diagram .The DB/OR - dark blue with orange trace wire would have to be shorted to one of those ground wire's for the compressor clutch to stay engaged .

buy a new one. It will be best.

You can check fisicaly the wires to the compressor and make sure you don't have any interuption on it. Can you hot wire the compressor from the battery ? But before you do it check the panel AC switch.