However, here's a general overview of the steps involved. This is not an exhaustive guide, and specific procedures may vary slightly depending on your truck's exact configuration:
1. Safety First:
* Refrigerant Recovery: This is crucial. You MUST recover the refrigerant from the system using a proper recovery machine. Releasing refrigerant into the atmosphere is illegal and harmful to the environment. This requires specialized equipment.
* Eye Protection: Wear safety glasses or goggles throughout the process.
* Gloves: Wear work gloves to protect your hands.
* Disconnect the Battery: Disconnect the negative battery terminal to prevent accidental short circuits.
2. Preparation:
* Consult a Repair Manual: Obtain a service manual specific to your 1991 Chevy 350 pickup. This will provide detailed diagrams, torque specifications, and specific procedures. A Haynes or Chilton manual would be helpful.
* Gather Tools: You'll need a variety of tools, including wrenches (metric and possibly standard), sockets, a compressor clutch tool (to remove the clutch from the compressor), a refrigerant line wrench set (specifically designed for A/C lines), possibly a vacuum pump (for evacuating the system after the replacement), and possibly a charging kit to recharge the system with refrigerant.
3. Removal of the Old Compressor:
* Identify Components: Locate the compressor, its associated hoses, wiring harness, and mounting bracket.
* Disconnect the Hoses: Carefully disconnect the high-pressure and low-pressure lines from the compressor. Use the appropriate A/C line wrenches to avoid damaging the fittings. Capture any remaining refrigerant in the lines.
* Disconnect the Wiring: Disconnect the electrical connector from the compressor clutch.
* Remove the Mounting Bracket: Remove the bolts securing the compressor to the engine block or mounting bracket.
* Remove the Compressor: Carefully remove the old compressor from the engine.
4. Installation of the New Compressor:
* Install Mounting Bracket (if necessary): If the bracket was removed, reinstall it securely.
* Install New Compressor: Carefully install the new compressor, ensuring it is properly seated and aligned.
* Connect the Hoses: Connect the high-pressure and low-pressure lines to the new compressor, ensuring a tight and secure connection. Use new O-rings if needed.
* Connect Wiring: Reconnect the electrical connector to the compressor clutch.
* Secure the Compressor: Tighten all mounting bolts to the manufacturer's specified torque.
5. System Evacuation and Charging:
* Evacuation: Use a vacuum pump to evacuate the entire system to remove any air and moisture. This is crucial for the proper functioning of the A/C system.
* Refrigerant Charging: Charge the system with the correct amount and type of refrigerant. This requires specialized equipment and knowledge. Improper charging can damage the compressor and other components.
6. Testing:
* Start the Engine: Start the engine and check for leaks. Observe the pressure gauges on the A/C system.
* Check for Proper Cooling: Ensure that the A/C system is producing cold air.
Again, I strongly emphasize that this is a complex procedure. Improperly handling refrigerants is dangerous and can result in injury or environmental damage. If you are not comfortable performing this repair, take your vehicle to a qualified mechanic specializing in automotive A/C systems. They have the proper tools, knowledge, and experience to complete this repair safely and correctly.
