2009 Mercedes-Benz S550 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.

A faulty air conditioning refrigerant pressure switch will prevent the air conditioner from operating properly. While a vehicle can certainly be driven without air conditioning, damage to the AC compressor is possible if the switch is bad and the system is used for extended periods of time.

The more the air conditioner is used - especially if it is turned on and off frequently - the shorter the lifespan of the pressure switch. Under normal operating conditions, the pressure switch should last the lifetime of the vehicle.

A technician will check the operating pressure in the air conditioning system to make sure it is in the proper range. If the pressure in the system is normal - not too high or too low - the technician will test the pressure switch (often by bypassing the switch and jumping the harness terminals) to determine if it is working - or if problems with the air conditioning system are the result of a different faulty component. For instance, a faulty high pressure switch might prevent the AC condensor fan from working properly, but the problem could also be a malfunctioning fan. A technician must be able to correctly identify whether or not the switch is at fault.

Once a technician has located and diagnosed a faulty pressure switch, replacement is usually straightforward.The electrical plug is disconnected from the end of the switch and the switch is unscrewed from its mount. It is common for the mount to employ a self-closing valve that prevents refrigerant from escaping when the pressure switch is removed. In most cases the refrigerant does not need to be removed (evacuated) from the system. however, it is necessary to have access to vehicle-specific technical information to ensure this is the case.

It is recommended that diagnosis and service to the air conditioning system be left to a professional who has access to specific information relative to the vehicle, and who can perform a comprehensive test of the system to accurately identify the source of the problem. The air conditioning systems on various vehicle makes and models will differ in design. Also, accidental discharge of refrigerant can be quite messy - and it is not lawful for refrigerant to be vented into the atmosphere. Special equipment is used for evacuation , vacuum, and recharging of the air conditioning system., should these operations be necessary.

Prolonged use of the air conditioning system with a faulty pressure switch - one that works intermittently - can lead to significant stress on the AC compressor and a significantly higher repair bill. The air conditioning system should be periodically inspected by a repair professional.

A common problem with DIY repairs of the air conditioning system include over-charging or undercharging with too much or too little refrigerant. An understanding of the relationship between temperature, pressure, refrigerant volume and weight is important for accurate charging of the system. Special gauges are also required. Although it is a fairly straightforward procedure to replace a pressure switch on most vehicles, because improper charging (pressure too high or too low in system) can mimic problems with the pressure switch, diagnosis and repair should be left to a professional.