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Pelican Technical Article:

Heater Valve Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$410

Talent:

**

Tools:

10mm wrench, flathead screwdriver, large bucket

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Heater valve

Hot Tip:

Get a really big bucket

Performance Gain:

Working heater

Complementary Modification:

New hoses

If you cannot turn off your heater, there is a good chance that your heater control valve has gone bad. The valve is powered in the close position which means when it fails it is stuck in the open position; this is so you always have use of your defroster and while being able to use your defroster is good it is not such a great thing when there is constant hot coolant in your heater core. Changing the valve is not difficult; you just need to remove the heat shield first to get access to it.

You can change the valve without draining the coolant but be prepared for some to spill. Se sure to catch and dispose of it correctly. This is also a good time to check your hoses and replace the coolant if necessary. Modern coolants last a very long time and if you need to drain your coolant to work on other parts of the vehicle you really should consider draining it into a clean container so you can reuse it. A couple of safety precautions/instructions you may want to observe before beginning: allow cooling system to cool down to a coolant temperature of less than 90°C. Open the cap of cooling system slowly; turn a conventional coolant cap as far as the first detent and turn a screwed coolant cap approx. 1/2 turn and release the pressure. Wear protective gloves, protective clothing and eye protection. Always dispose of used coolant in accordance with the regulations in your region; NEVER pour coolant down a drain, into the ground or a sewer.

The heater valve is located behind the engine on the right side of the bulkhead behind the heatshield (red arrow).
Figure 1

The heater valve is located behind the engine on the right side of the bulkhead behind the heatshield (red arrow).

Remove the four 10mm screws (red arrows) holding the shield in place and remove it from the engine compartment.
Figure 2

Remove the four 10mm screws (red arrows) holding the shield in place and remove it from the engine compartment.

You can now access the heater valve (red arrow).
Figure 3

You can now access the heater valve (red arrow). Begin by pulling the wiring connection off of the top of the valve (yellow arrow).

Use the appropriate tool for removing the two hose clamps on your heater valve (red arrows).
Figure 4

Use the appropriate tool for removing the two hose clamps on your heater valve (red arrows). You can use a flathead screwdriver and remove the side hose but it is easier to remove the lower hose once the valve is disconnected from the bulkhead.

Use a 10mm wrench and remove the two bolts holding the valve in place (red arrows).
Figure 5

Use a 10mm wrench and remove the two bolts holding the valve in place (red arrows). The right side bolt has a fastener on the bottom that you will need to secure while removing the bolt.

You can now remove the valve and replace it.
Figure 6

You can now remove the valve and replace it. Installation is the reverse of removal and do not forget to top up any lost coolant.

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Page last updated: Wed 12/7/2016 03:02:51 AM