Your car air conditioner stopped cooling – how do you determine what is wrong with it? Here are some test procedures to use and get to the problem. Hopefully this will help you understand some of the causes and cures for an air conditioner that is not working.
Of course, some car AC repairs are best left to a professional technician because of the skills and tools required. If you are not comfortable performing these repairs, or if you do not have the right equipment, do not hesitate to take your vehicle to a professional – they will follow any version of the process described below.
Electrical and mechanical AC elements
Start the engine and turn on the AC, then open the hood and observe the compressor. Is the clutch engaged and the compressor shaft rotating? If not, there are several things to check, starting with the fuse.
If the compressor looks good, proceed to the low pressure switch, usually mounted on the suction hose near the evaporator or on the accumulator / receiver wiper. Disconnect the wiring harness from the low pressure switch and jumpers on the wiring harness with a jumper wire. If the connection now goes together, you look at two possibilities ̵
If the clutch does not engage the low pressure switch, turn off the engine and disconnect the wiring harness from the compressor clutch. Using a multimeter, check for continuity and resistance across the two poles of the coupling magnet. If the test shows an open circuit, the windings of the coupling magnet burn. Repair or replace if necessary. If it shows continuity and a low ohmic reading, then measure the distance of the clutch shoe from the magnet.
Determine the distance between the clutch shoe (sometimes called a plate) and the clutch magnet using a track gauge. The measurement should be between 0.020 “and 0.010”. If the reading is over 0.020 ”, the shoe must be removed and a washer removed from the shaft to allow the shoe to be reassembled at the correct distance.
Shoe removal requires a special puller intended for the specific compressor. Attempting to remove the clutch shoe without proper tools will result in damage to other compressor components that far exceed the cost of the shoe puller.
Connect a manifold gauge
If the compressor will rotate, but the air conditioner does not cool down, it is time to connect a refrigerant manifold to the AC system and check the system pressure with the engine running and the air conditioner on.
Connect the blue hose to the suction port and the red hose to the pressure port. Open the measuring valves and observe pressure readings. If the pressure does not check the specified readings according to the service manual, it is possible to add some refrigerant as a test to try to get the system back into operation.
If the reading of the pressure gauge is high while at the same time the reading of the suction side gauge is low, a blockage in the system line is suspected. The plug is probably at the expansion valve / opening pipe as this is a limited flow point where the expansion of refrigerant takes place to enable cooling. This will require refrigerant recovery and opening system to access the expansion valve / opening pipe and clean or replace as needed. The entire system must be flushed before reconnecting the components, vacuuming and charging with coolant.
The compressor can rotate but does not pump due to internal damage. If the suction side and the pressure gauges show almost the same pressure readings while the compressor is rotating, this indicates that the compressor has failed. Replace a failed compressor and flushing, vacuuming and charging systems require equipment that the average DIYer probably does not have.
Lack of air flow over evaporator and condenser
The condenser (in front of the radiator) must have a good air flow to facilitate heat transfer to cool the hot coolant and in the same way the evaporator (embedded under the line) must have good air flow to distribute the cooled air inside the vehicle which is provided by a fan that forces air movement. Make sure there is no debris or debris blocking the airflow. Clean if necessary for maximum airflow.