Things You'll Need:
- Set of air conditioning gauges
- Volt and ohm meter
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Step 1
Start the vehicle and turn the air conditioning on. If there is a scraping, tinny sound just when the compressor is turned on and goes away as soon as it is turned off, only the clutch needs to be replaced (as long as the compressor is still good in the subsequent tests). The clutch can be replaced without discharging the air conditioning system (if it is accessible). Just remove the belt and leave the compressor mounted to the engine.
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Step 2
Check the clutch operation if it does not come on. Apply power directly to the wire on the top front of the compressor. If it comes on, then there is an electrical problem to be traced. If it does not come on replace it.
If there is a rather loud knocking noise as the compressor operates and goes away when the air conditioning is turned off, the compressor is about to self destruct internally and should be replaced as soon as possible. Do not use the air conditioning until it is replaced, as the vanes inside the compressor are coming apart and the more it is run the more material it will release into the system, causing a blockage. This could get very expensive if all the parts need to be replaced in the air conditioning system. -
Step 3
Put the gauges to the air conditioning system and turn the air conditioner on. If the compressor does not come on, check the pressure on the gauges. The blue (low side) should be around 75 to 80 pounds in order to kick the compressor on. If the pressure is below 75 pounds the system needs to be charged in order to get the switch to activate, allowing the compressor to work.
The low side switch is installed so that if the pressure drops (usually a leak causes this), it shuts the compressor off, preventing damage to the same. If the pressure is correct and in range then an electrical problem is present. -
Step 4
Check the low side switch for power with the air conditioning on. If there is power, jump the connector and see if the compressor comes on. If it does, the switch is bad. If there is no power, check the fuse for the air compressor in the fuse relay box under the hood. Check the relays by pulling them out and checking the terminals for power at two terminals. If there is power at only one terminal, the problem is inside the cabin. If it has power at two locations the relay is bad.
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Step 5
Check the gauges if the air conditioning comes on and does not cool. The proper readings will vary a little with the outside temperature but should be close to 25 to 40 pounds on the low side (blue) and 210 to 250 on the high side (red). If both sides are low and the compressor is working the system needs to be charged. If the high side is low and the low side is high the compressor is no good. If the high side is high and the low side is close to normal there is either a blockage in the expansion valve or orifice tube, a radiator fan not working or a plugged up condenser.
