Mercedes-Benz ML550 Air Conditioning Refrigerant Pressure Sensor Replacement Cost

Air conditioning systems function by changing the phase of refrigerant between hot and cold liquid and gas. This allows some portions of the system to remain hot while other portions cool the inside of the vehicle. The system is divided into one high and one low portion, and both sides are pressure monitored by air conditioning refrigerant pressure sensors to protect the system in the event of a failure.

On the high side, the high pressure sensor observes pressures to ensure the compressor is creating the needed line pressure to cycle refrigerant through the system, and the low side pressure sensor ensures the high pressure liquid has been converted to a low pressure gas in order to cool the evaporator core. If these sensors read incorrect pressures, they will report it to the control module, which will turn off the air conditioning compressor to prevent failure.

A malfunctioning high or low pressures sensor will cause the air conditioning compressor to cease function, may cause the air conditioning light to blink, or may allow the air conditioning compressor to run although line pressure is incorrect. Operation of the air conditioner is likely not intermittent, but will fail altogether.

There is no necessity to repair the air conditioner immediately. Replacement is based on convenience and comfort alone. In some locations, the heat outside may be sufficient to consider using a vehicle with no air conditioner a health risk for children or seniors, so this would raise safety concerns.

Air conditioning high and low pressure sensors are among the most common components that cause air conditioners to fail. This can be due to liquid in the system, external damage, wiring issues, or the sensor may be reporting a high or low pressure problem. Typically, these sensors will last quite some time before needing replacement, but failure can occur at any time.

Diagnosing the air conditioning refrigerant line pressure sensors is as easy as connecting a set of gauges to the high and low side service ports, monitoring the pressures, and comparing those to the values sent from the sensors to the control module. If the values show high correlation, the control module may be malfunctioning, or there is a fault in the refrigerant system. However, if there is incongruence, the sensor circuit will be verified before replacing the sensor.

Replacing these refrigerant pressure sensors requires the system to be evacuated of all refrigerant, the sensor unscrewed and replaced, and then recharging the system. If the vehicle uses an orifice tube, the technician will likely recommend replacing it while the system is discharged, and if signs of water contamination are present, the receiver drier or accumulator should be replaced as well. Finally, the system can be recharged, and the air conditioning system will be tested to prove the repair.

We do not recommend the use of any off the shelf air conditioning refill products. These seldom work, and will cause clogs in the system and the expensive refrigerant recovery machinery. When the air conditioner needs service you can save time and cost by having a technician repair it properly the first time.

Discharging refrigerant into the atmosphere is hazardous to the individual releasing the refrigerant, and will cause harm to the environment. State and federal statutes prohibit this action, and all refrigerant must be extracted using a refrigerant extraction machine and recycled. Since a technician must vacuum the system to perform any refrigerant system repair, it is most wise to allow the technician to extract and recycle the old refrigerant also. Older vehicles will be required to retrofit the air conditioning system for newer, more environmentally friendly types of refrigerant, and this will cause additional costs during the air conditioning repair.

This is not a repair that can be performed by the DIY mechanic unless refrigerant recovery equipment and vacuum and recharge equipment are on hand. Since this equipment is very costly, the most cost effective option is to have the air conditioner serviced by a professional.