How to Check for a Bad A/C Compressor
Automotive air-conditioning compressors circulate Freon coolant through the system, cooling the interior through air induction using a condenser. This compressor can fail because of age or lack of lubricant, and require replacement. The average backyard mechanic can troubleshoot the system and discover a bad compressor in about half an hour. Disconnect the battery for 30 minutes to reset the computer, which could cause A/C malfunctions in rare instances.
Other People Are Reading
Instructions
-
Electrical
-
1
Inspect the compressor's connection to the wiring harness, which is typically on the top of the compressor housing between the clutch and the body. It should be securely connected to the two- or three-blade style connectors within it. You can test it by pushing it into the connector lightly. If it was loose, pull it off and inspect the inside of the plug. The blade catches should be tight and shiny.
-
2
Check the fuse panels for fuses with blown elements. Most cars have a primary and secondary fuse box. The primary fuse box powers the engine and important subsystems; the secondary is redundancy for the interior and low-power accessories. The primary is under the hood on the driver's side fender, inside the engine bay. The secondary is usually at the driver's side kick panel. Look closely and pull suspect fuses; replace any that are blown.
-
-
3
Turn the A/C control panel to the "A/C On" position with the engine running, and watch the compressor clutch for movement. The clutch should activate when the A/C is turned from on "Off" to "On." The compressor will also sound a loud tick when the clutch engages. If the compressor clutch fails, or locks into place and begins to squeal, you must replace the compressor. The heat from a seized clutch can damage internal bearings.
Freon and Lubricant
-
4
Check for leaks by injecting an ultraviolet dye into the air-conditioning system. The dye will glow under a black light, and if it is coming from the compressor area, then there may be a line gasket leak or internal bushings that have failed. Replace the line gaskets first by evacuating the system (at a professional facility only) and removing the bolts. Replace the gasket, and reattach the lines. Recharge the system with Freon and more dye, and check for a leak in the same area.
-
5
Recharge the system with more lubricant if the compressor is noisy while in operation. Noisy compressors usually indicate a lack of oil, and the average mechanic can refill a system without evacuating it by using a refill kit. This kit is just a valve with an adapter for a can of Freon, as well as a nozzle. The nozzle attaches to the low-pressure side of the A/C system, and you add a can of lubricant to the system while it is running. The vacuum of an operational compressor will suck the oil from the can. Remove and discard the can, but save the kit for a later fill if the system still leaks Freon. The compressor should immediately become quieter as the oil is sucked into the system.
-
6
On older models, listen for a hissing sound from the dashboard when turning the system on; this could indicate a vacuum leak in the control panel. The vacuum tubes that cause the mechanical action of airflow and actuate the electrical compressor connection could be damaged.
-
1
Tips & Warnings
Never discharge Freon into the atmosphere; garages will evacuate it for free.
