How do I Troubleshoot an Air Conditioner for a 1991 Chevy Truck?

by Ross Glyn
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Problems that may arise with the air conditioning of your 1991 Chevy truck are usually simple to diagnose, whether it's an issue with a leaky AC hose or a defective magnetic clutch. Run through a few basic troubleshooting steps before taking your Chevy in to an AC mechanic for what could turn out to be an expensive service.

Step 1

Start the engine and switch on the electric blower fan and AC to ensure the AC controls are operating correctly. If the controls are loose or difficult to move, have them replaced. If the fan does not turn on, a fuse may have blown, or the fan itself could be faulty.

Step 2

Inspect the fuse box for any blown or damaged fuses. The fuse panel (depending on the model of truck) is usually located under the dashboard on the left side of the steering wheel. Consult the diagram on the inside of the fuse box cover for instructions on how to identify the fuse corresponding to the AC system. If the fuse is broken, replace it with another of the exact same amperage rating.

Step 3

Check the two AC/heater hoses (with the engine running) under the hood. The hoses protrude from the firewall and are roughly the thickness of a garden hose. The firewall is the metal division that separates the engine compartment and the passenger compartment. Place your hand on the two hoses. They should both be warm to the touch. However, one should be cooler than the other. If it is not, it could indicate that the valve control is bad. Have a qualified mechanic investigate this further, as the valve control may need to be replaced.

Step 4

Turn the AC up to the highest setting (with the engine running) and check under the hood to see if the magnetic clutch connected to the AC compressor engages. If it does not spin, this could indicate that the system is low on refrigerant. Have a mechanic refill the system. If the magnetic clutch is receiving voltage but is not engaging the compressor, the clutch may be defective and need to be replaced.

Step 5

Inspect all the AC hoses for any leaks. If you notice an excessive amount of green, oily residue on the hoses, they may need to be replaced.

Step 6

Check the AC system (with the engine turned off) for adequate pressure. Remove the black caps from the service ports on your Chevy Truck's AC unit. Screw the blue hose to the low-side service port and the red hose to the high-side port. The test gauge has a red pressure monitor and a blue monitor from which to read the pressure. If the reading is not between 50 and 80 psi it could indicate a leak within the system. Have a qualified mechanic investigate further for you.

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