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Pelican Technical Article:

Replacing the Double Contact Relay

Time:

2 hours2 hrs

Tab:

$25 to $120

Talent:

**

Tools:

Flathead screwdriver, 8mm socket, 20-inch extension,

Applicable Models:

Mercedes-Benz R107 (1973-80)

Parts Required:

Vacuum switchover valves

Hot Tip:

Label the vacuum lines with a masking tape

Performance Gain:

Working climate control

Complementary Modification:

Change switchover valves

If your blower motor isn't blowing anymore and you made sure the fuse wasn't blown, it is possible that the double contact relay has failed.

In order to get to the double contact relay, the glove box must be removed. See our article on removing the glove box

Before you do any work on your car it is important that you wear safety glasses, work gloves and dispose of all fluids in a safe manner. Protect your eyes, hands and body from dust, debris as well as sharp objects and edges while working on your vehicle. Disconnect the battery before beginning work. Never work on your vehicle if you feel the task is beyond your ability.

Using a flathead screwdriver, pry off the plastic fastener that holds the glove box in place.
Figure 1

Using a flathead screwdriver, pry off the plastic fastener that holds the glove box in place. Be careful not to break the inset or the fastener. There will be two fasteners to remove.

Lift the glove box out from the instrument panel.
Figure 2

Lift the glove box out from the instrument panel.

Once the glove box is out, you will see the vacuum switchover valves located to the right side of the cavity.
Figure 3

Once the glove box is out, you will see the vacuum switchover valves located to the right side of the cavity. They are color coded with representative lines. You can start by pulling out the electrical jack located at the front.

Next notice the terminal jack which sends signals for all the valves.
Figure 4

Next notice the terminal jack which sends signals for all the valves. This can be removed by slipping the metal clasp downwards and pulling the jack straight out.

The vacuum lines can now be removed.
Figure 5

The vacuum lines can now be removed. The yellow check valves are an easy starting point. Labeling each with masking tape and indicating which line feeds which switch is very important.

Pull off each jack that is connected to each switchover valve.
Figure 6

Pull off each jack that is connected to each switchover valve.

Using an 8mm socket and a 20-inch extension, loosen and remove the three bolts holding the switchover valve plate.
Figure 7

Using an 8mm socket and a 20-inch extension, loosen and remove the three bolts holding the switchover valve plate.

Using wire-cutters, locate the lines connecting the switchover valves and clip the cable tie.
Figure 8

Using wire-cutters, locate the lines connecting the switchover valves and clip the cable tie. The cable bundle will be located towards the driver side.

The bank of switchover valves with the double contact relay are now free.
Figure 9

The bank of switchover valves with the double contact relay are now free.

The double contact relay can be removed from the valve bank using a Phillips head screwdriver.
Figure 10

The double contact relay can be removed from the valve bank using a Phillips head screwdriver. Installation is the reverse of removal.

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Comments and Suggestions:
Panther Comments: Turning the 450SL off I have a buzzing noise ,Can not start the car. Disconnect the battery it stops Which relay switch does anything it is & location ?
October 25, 2015
  Followup from the Pelican Staff: hard to say. Check the electrical box in the engine compartment for the location of the sound. COuld just be bad connection. - Nick at Pelican Parts  

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