1998 Mercedes-Benz S420 Air Conditioning Refrigerant Pressure Switch Replacement Cost

The air conditioning refrigerant pressure switch is a safety component of the AC system that senses when the pressure in the system is either too high or too low, both of which can cause damage to the AC compressor. If a high or low pressure situation is detected, the switch turns the compressor off to prevent damage. Some vehicles have bot a high and low pressure switch, while others have one of the two.

The air conditioning refrigerant pressure switch monitors the pressure cycling through the AC system. Refrigerant in the system is, at some points, under low pressure, and, at others, under high pressure. This essentially creates two "sides" to the system: the low side, and the high side. Generally, there are two pressure switches. A low pressure switch disengages the compressor clutch when the pressure is too low on the suction side (low side) of the AC system in order to protect the compressor from damage. A high pressure switch does the same thing if pressure builds too high on the discharge side (high side) of the system. It may also control the AC condensor fan. Some vehicles have only one switch.

If the air conditioner is turning on and off frequently, or not turning on at all, the air conditioning refrigerant pressure switch might be faulty. Even a system that is unable to cool the vehicle properly can be a sign that the pressure switch has failed. The pressure switch is tasked with cutting off power to the AC compressor if the pressure in the system is either too low (on the "low side") or too high (on the "high side"). An AC system that cycles on and off is normal. Just as a household air conditioner turns on and off as needed to maintain a consistent temperature, the AC system in a vehicle will turn on when the temperature in the passenger compartment rises, and turn off when it is cool. But constant and frequent cycling of the AC compressor is not normal, and may be due to a faulty pressure switch. And if the switch is not working at all, the compressor may not turn on at all. The high and low refrigerant pressures in the AC system are key to the operation of the system. If the pressures are too high or too low because a pressure switch is faulty, the system may have a difficult time cooling the vehicle.