The ac compressor does not come on w/ switch. i would check the fuse but i do not know what one it is

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.

You say refrigerant is "full", but it can have too much. If you have attempted to "top off" your refrigerant then you may have too much, keeping the compressor from engaging. If you haven't messed with it and the compressor just stopped engaging on it's own then I would start checking the relay, fuse and the ac switch.

Defective compressor clutch, or ground fault in the ac switch circuit.
Disconnect lead to compressor from ac switch.
Run a fused line from the battery to the compressor, if it works without blowing the fuse, check for fault in the AC switch circuit.

There should be a 15amp fuse for the compressor in the box next to the battery, also a wide open throttle relay and two pressure switches that can prevent power to the ac clutch.

check your fuse box for a blown ac fuse, fuse box usually under dash, sometime under the hood of the car usually on drivers side. bad switch?
check if you hot wire lead might be pinched and grounded out or broken wire between battery and switch

I purchase atruck and they put a wire from the compressor ac to fuse box. I want to eliminate that because ac compressor is always on. I check the ac heater selector switch and is ok. What if they take the fuse of ac out and bypass with a wire. Wich number in the chart fuse box is the compressor switch

CHECK AC COMPRESSOR FUSE OR RELAY.IF BOTH FUSE/RELAY GOOD.PROBABLY YOUR REFRIGERANT TOO LOW.FAULTY AC REFRIGERANT PRESSURE SWITCH OR OPEN AC COMPRESSOR CLUTCH COIL OR PROBLEMS WITH THE PCM.

CHECK AC COMPRESSOR CLUTCH SHOULD BE ENGAGED OR RUNNING WITH AC SWITCH ON POSITION.IF NOT CHECK AC COMPRESSOR CLUTCH FUSE AND RELAY.IF BOTH GOOD AND POWER IS GOING TO AC CLUTCH.YOUR CLUTCH IS OPEN.IF ALL LOOKS GOOD YOUR AC LOW PRESSURE SWITCH IS BAD.COMPRESSOR SEIZED OR YOU HAVE TOO MUCH MOISTURE IN AC SYSTEM.

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.