Why does the heat in your 1991 Chevy Caprice work and not the air conditioning?

Answer 1

Automotive Air Conditioning is a dangerous place. It uses metal reinforced high pressure hoses and (often environmentally damaging) gas under pressure.

The two systems share a very few components but are mostly independent.

They normally use the same plastic vent system inside the dashboard (and it's controls) and the same fan to cause the air to move.

Otherwise they do not interact.

The heat is a byproduct of the water cooled engine. As the engine runs the heat generated is transfered to the water inside the engine and then circulated out to the radiator where it bleeds off though the radiator coils.

When you turn the heater on the hot water also flows through a much smaller radiator (the heater core) that is located inside the dash. The fan pushes air through the heater core and you get heated air inside the car.

The cooling is done with a similar but separate 'radiator' in the car that cools the air blown past it by the fan.

The Air Conditioning cools using compressing/expanding freon and centers around the AC compressor that is attached to the motor. A very common failure for older cars is the main seal in the AC compressor. Seal failure allows the freon to escape and since there is nothing to compress, no cooling happens.

Other possibilities include: the AC switch inside the car, the AC compressor clutch (this allows the outside ring of the AC drive wheel to spin free unless the AC is needed), or a simple lack of freon.