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A/C Pressure Switch Replacement
 
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Pelican Technical Article:

A/C Pressure Switch Replacement

Steve Vernon

Time:

30 minutes30 mins

Tab:

$10

Talent:

*

Tools:

27mm wrench or deep socket

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Switch

Hot Tip:

Make sure you are replacing the right switch

Performance Gain:

Proper A/C cooling

Complementary Modification:

Recharge the A/C

The air conditioning system on the W123 has two sensors on the receiver/dryer; one is a pressure sensor and the other is a temperature sensor for the auxiliary fan. The pressure sensor needs to be functioning for the A/C system to work. If your sensor has failed it can be replaced relatively easily with the exception that the sensor sits in the actual flow of the coolant and cannot be changed without removing the refrigerant from the system first. If you just try and remove the sensor you will quickly vent the refrigerant to the atmosphere which is dangerous and illegal so make sure to have your refrigerant removed and stored to reinstall after you replace the sensor.

The switch is located in the right front lower section of the engine bay and depending on whether you are using a 27mm deep socket or 27mm wrench can be changed without removing other components. We removed the air box on our 300TD to get better pictures of the procedures but you should be able to get your hands in there and replace it without pulling the box if you are using a deep socket. If you want more room to work please see our article on air box filter removal for further instructions.

Over the years your car may have been serviced by multiple people including previous owners and this can lead to parts replaced with different size fasteners and hardware. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches. If something is different on your vehicle please let us know and share your info to help other users. If you have any questions or comments or even a different procedure you would like to share please leave it below and please leave your vehicle information.

The receiver/dryer is located in the lower right front of the engine bay (red arrow).
Figure 1

The receiver/dryer is located in the lower right front of the engine bay (red arrow). You should be able to change the switch out without moving anything else but if you want to pull the air filter box on the newer Turbo diesels please see our article on how to do this. Remember unless your system is empty of refrigerant you will illegally vent the refrigerant to the atmosphere if you remove the sensor before safely discharging it.

There are two sensors or switches attached to the receiver/dryer.
Figure 2

There are two sensors or switches attached to the receiver/dryer. The one that comes off the "T" on the top is the temperature switch (yellow arrow). The other switch (red arrow) is the pressure switch and is in the stream of the coolant; if you accidentally remove or open this switch you will vent the refrigerant into the atmosphere (which is illegal) and lose all of your coolant.

Remove the two wires connections for the switch apart.
Figure 3

Remove the two wires connections for the switch apart.

Use a 27mm wrench or deep socket and remove the switch from the receiver/dryer housing.
Figure 4

Use a 27mm wrench or deep socket and remove the switch from the receiver/dryer housing.

This photo illustrates how the sensor sits in the refrigerant flow, once you have the sensor out it is very important that nothing gets in this opening (red arrow).
Figure 5

This photo illustrates how the sensor sits in the refrigerant flow, once you have the sensor out it is very important that nothing gets in this opening (red arrow).

The sensor must have a small rubber O-ring on the bottom to assist in sealing the opening and helping keep the system pressurized.
Figure 6

The sensor must have a small rubber O-ring on the bottom to assist in sealing the opening and helping keep the system pressurized. Installation is the reverse of removal.

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Page last updated: Mon 12/5/2016 03:01:24 AM