This is usually an indicator that the throttle body needs to be cleaned. This is an easy job if you know anything about throttle body loction. Remember that the Battery must be disconnected first. Remove the plastic resonator on top of the motor. It has the Vortec 4200 on it. Remove the hoses and electrical connections to the throttle body. 4 bolts hold it in place. (10mm?) Once removed you will see that the back side and mating surfaces get incredibly dirty and you can then manually open the butterfly and scrub the dirty parts with an appropriate cleaning solution and an old toothbrush. Not only will it cure the AC problem but it will make your truck idle and accelerate smoothly again.
Give the engine some extra fuel and see what happens when you turn on the AC. If there is still a problem then the compressor or AC clutch could be bad. If its ok then the fast idle needs to be looked at to find out why the car does not idle up when the AC is on.
When you turn the ac on it engages the ac clutch which is turned by a fan belt which is turn by the engine. you are making the engine work harder. The idle speed might be set to low or it,s time for a tune up.
The A/C idle compensator solenoid is not functioning. This should be located next to the carb.
The idle speed control solenoid controls the idle of the engine when the air conditioning is engaged. Since the ac pump draws down the engine idle the solenoid increase the idle when the ac is on.
An idle motor controls the idle-like when U turn on the AC,It will raise the RPM's so the engine doesn't stall. Idle motors are used on computer cars & instead of a screw adjustment.
An engine usually has a higher idle speed when the ac is running. If the high speed idle does not operate then the ac will cause the engine to stall.
probably got a bad IAC motor
The idle compensator speeds up the engine when the ac is turned on to compensate for the additional load on the engine. If the engine is surging when the ac is on and not any other time then the compensator is probably bad. If it surges all the time but gets worse when the ac is on then look for an intake vacuum leak.
The engine idle may be set to low to compensate for the AC compressor starting up. Rev the engine a few times to see if it stops. If it doesn't, there may be a problem with the AC temperature signal or motor mount.
This switch compensates for the rpm that are lost when you turn on the ac in your vehicle. The ac puts an extra load on the engine that this switch then compensates for and puts your rpm back to where they belong.
Most likely is a bad ignition switch.
Running your Air Conditioning puts a load on the engine - this is normal, the engine is working harder when you turn it on. You'll get worse gas mileage as a result.