What if My Silverado Compressor Will Not Engage?

by Erik Johnson
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When the air conditioning quits working on your Chevrolet Silverado pickup, the first thing to do is to open the hood and verify that the compressor is properly engaging. A compressor that won’t engage can often be fixed by a home mechanic for a very small cost by checking the electric components and refrigerant level. More serious issues must be handled by a trained technician.

Fuses and Relays

The first thing to check if your compressor will not engage is the electrical system. Check the fusebox first, which is located under the hood near the driver’s side fender on 1999 through 2010 Silverado model years and on the left side of the instrument panel on older models (refer to your owner's manual). Locate the red 10 amp fuse marked A/C COMP and remove it. If the metal ribbon within the fuse appears burnt or broken, replace the fuse. If the fuse is okay, the next suspect is the air conditioner relay. This relay is also located in the fuse box, though there’s no visible indicator to verify that it’s in working order. Most auto parts stores can test this relay for you, though it’s uncommon for this relay to fail on Silverado pickups. A new relay can be installed for less than $20.

Refrigerant Pressure

If the fuses and relay are in working order, your air conditioning system may be inadequately charged with refrigerant. Sensors within the system detect when the pressure of refrigerant drops below as certain level and won’t engage the compressor to avoid damaging it. Silverado pickups produced after 2000 use ozone-friendly R-134a refrigerant. Older models originally used R-12 refrigerant, commonly known as freon, though many trucks have been retrofitted to use R-134a. Home R-134a charging kits are available. Start your engine and turn your air conditioning to the coldest setting. Connect the charging hose to the can of refrigerant and then to the low pressure port of the air conditioning system. On most Silverado models, this port is located on the accumulator: an aluminum cylinder located on the passenger side of the engine compartment. Hold the can of refrigerant upright and slowly open the valve on the charging hose. The pressure of your can will force the gas into your system. While the compressor may engage immediately, allow the can to empty before removing the charging hose. Test the pressure of your system with an air conditioning gauge and do not charge it over capacity.

Professional Help

A compressor that won’t engage after refrigerant charging indicates deeper problems with your air conditioning system. It could indicate faulty pressure sensors, damaged wiring or a bad HVAC control module. These issues must be tested with a mechanic’s diagnostic scan tool and should be left to a General Motors certified air conditioning technician.

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