A/C compressors are difficult to work with because of the refrigerant stored inside. When a compressor clutch does not disengage, it will cause the refrigerant to build up and freeze the line. To disengage the clutch, a switch must be replaced.
The Low-Pressure Switch
The low-pressure switch tells the car that the clutch needs to engage and disengage and will shut off the A/C compressor. When the switch goes bad, it will no longer be able to measure pressure and will leave the clutch engaged the entire time. This switch is located on the metal canister next to the compressor. It is screwed into the refrigerant canister and has two wires extending from it toward the wiring harness.
Because the switch is a connection between the canister and the condenser, the refrigerant must be drained from the canister. It is illegal to drain this into the air; it will have to be drained by a professional company. Once the canister is drained, unscrew the switch from the canister with a wrench. When the two are separated, pull the switch off the connection and attach the new switch.
Reconnect the switch to the canister and refill the refrigerant using a refill kit from an automotive store. Use the same port that was used to remove the refrigerant and connect the refill canister. Fill it up until the pressure indicator on the refill canister stops moving and disconnect the refill canister. Start the car and let it run to ensure the compressor clutch disengages.