3. Faulty AC Pressure Switches
An AC pressure switch is a safety device that monitors the pressure in the AC system. It is made up of a diaphragm, a spring, and a switch.
The pressure of the AC is monitored by the diaphragm, and when the pressure reaches a certain level, the switch will be triggered and will turn the compressor off.
Most AC systems have two pressure switches, a low-pressure switch, and a high-pressure switch. The low-pressure switch is triggered when the pressure in the system is too low, and the high-pressure switch is triggered when the pressure in the system is too high.
When the pressure in the system is too low, the low-pressure switch will be triggered, and the compressor will be turned off. This is done to prevent the compressor from running dry, which can cause damage to the compressor.
When the pressure in the system is too high, the high-pressure switch will be triggered, and the compressor will be turned off. This is done to prevent the compressor from overheating, which can also cause damage to the compressor.
When the pressure switch is off, the current will not flow through the AC compressor coil. As a result, the compressor will not engage.
If either the low-pressure switch or the high-pressure switch is faulty, it can cause the compressor to cycle on and off every 5 seconds. This is because the faulty pressure switch will keep sending false readings to the compressor, causing it to turn off and on in short intervals.
How to spot it?
To test the AC pressure switch:
- Turn the AC on to full-bast mode.
- Connect one end of the multimeter’s test leads to the wire of the AC pressure switch and the other to the ground.
- Turn the multimeter to the Ohm setting.
- Start the car and turn on the AC.
- The multimeter should read zero as the pressure switch is closed when the AC is on and an open circuit when the switch is open. If the multimeter reads differently, the switch may need to be replaced.