The AC pressure switch is part of the air conditioning (AC) system in your vehicle. Also known as a refrigerant pressure switch, this device senses when the pressure inside the AC system is either too high or too low and disables the AC compressor to prevent damage to the system.
As is the case with any AC system, including the one in your vehicle, refrigerant inside undergoes a series of pressure changes as it passes from a gas to a liquid and back again. The AC compressor compresses gaseous refrigerant and pumps it through a tube to the condenser, where the high-pressure gas becomes a high-pressure liquid. From there, the refrigerant travels to the expansion valve where it transforms into a low-pressure liquid. Finally, it goes to the evaporator and becomes a low pressure gas once more before returning to the compressor to begin its journey again.
It is in the evaporator that heat is drawn from the passenger compartment and cool air is blown in. But if, at any point in the process, the pressure of the refrigerant rises too high or falls too low, then damage can occur to the AC system. The AC pressure switch is in place to make sure this does not happen. Some vehicles rely on a low pressure switch, others a high pressure switch. Some include both.
To replace an AC pressure switch, a technician will likely disconnect the battery, taking care to preserve the memory of your vehicle’s computers. From there, the task of replacing the switch itself is not, in and of itself, a complex repair on most vehicles. That said, it is important for the technician to have access to vehicle-specific repair information to determine whether or not the refrigerant must be evacuated from the AC system.
On most vehicles, the refrigerant does not need to be removed and replaced, as long as other components are not also being replaced along with the AC pressure switch. That is because its mount is typically equipped with a special valve that closes to keep the refrigerant in place when the switch is removed. Therefore, in order to replace the switch, a technician will unplug the wiring from the switch, use a wrench to unscrew the body of the switch from its mount, and insert a new switch in its place.
Once the wire has been plugged into the new switch, the technician will start your vehicle and run the AC system to verify that the repair was successful.