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HVAC Temperature Sensor Replacement
 
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Pelican Technical Article:

HVAC Temperature Sensor Replacement

Steve Vernon

Time:

30 minutes30 mins

Tab:

$10 to $50

Talent:

**

Tools:

19mm deep socket, rags

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

HVAC temperature sensor

Hot Tip:

If you are really quick you don't need to drain the coolant

Performance Gain:

Working blower motor

Complementary Modification:

Coolant flush

There is a blower motor sensor located on the top right side of the motor between the valve cover and the EGR valve. This sensor stops the blower motor from running until the coolant has reached 33 degree C. Once 33C has been reached the blower motor circuit is provided a ground from the sensor and this allows the blower motor to function. If your sensor has failed replacement is quick and easy and if you are fast enough you can do it without draining the coolant from the vehicle. Just remember to check the level after you have installed the new one and top up the coolant as needed.

Whether you are draining the coolant to a level below the switch or just changing it fast make sure that you are working on a cool car. Please see our article on radiator flush and fill if you want to drain the coolant.

Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. 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.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

The HVAC or blower motor sensor is located on the right side of the motor between ERG valve and valve cover (red arrow).
Figure 1

The HVAC or blower motor sensor is located on the right side of the motor between ERG valve and valve cover (red arrow).

Locate the senor and pull the electrical connection off of the top (red arrow).
Figure 2

Locate the senor and pull the electrical connection off of the top (red arrow).

Use a 19mm deep socket to fit over the senor and remove it from the engine (red arrow).
Figure 3

Use a 19mm deep socket to fit over the senor and remove it from the engine (red arrow).

Use care when removing the sensor as this area can get very dirty and you do not want anything falling into the opening.
Figure 4

Use care when removing the sensor as this area can get very dirty and you do not want anything falling into the opening. If the opening is dirty or corroded make sure to carefully clean around the area so you can get a good seal (red arrow).

Always install a new crush washer when installing the sensor.
Figure 5

Always install a new crush washer when installing the sensor. The crush washer on our sensor was stuck to the engine so make sure you account for the old one and install a new one. Installation is the reverse of removal and do not forget to check the coolant level.

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Comments and Suggestions:
Frank Comments: I need to order one of these 33 deg C temp sensors.

What is the part number, please ???
August 5, 2016
  Followup from the Pelican Staff: You didn't mention your vehicle info. So I can't try to look it up.

For an instant response, give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need. - Nick at Pelican Parts
 

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