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Pelican Technical Article:

Heater Valve Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$700

Talent:

**

Tools:

13mm, 10mm socket, pliers, flathead screwdriver, large bucket

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

New heater valve

Hot Tip:

Work on a cool car

Performance Gain:

Proper HVAC heat

Complementary Modification:

Radiator flush

If you are having trouble with your climate control system on your W124 from no heat to heat all the time, one of the issues can be the heater valves. The heater valves allow hot coolant from the engine to circulate through the heater core and warm the HVAC system. If you are only getting cool air from your system even with the heat turned to MAX, or you get nothing but hot air all the time you may have a faulty heat valve. One of the ways to check is to carefully place your hands on the heater core hoses to tell if warm coolant is flowing through them while the heat is turned on. Use care as the coolant and hoses can get very hot.

The valves also use the hot coolant to heat the windshield wiper fluid on the vehicle.

This article will show you how to replace a faulty heater valve. Begin by working on a cool car. You will be working with the coolant and do not want to burn yourself. You do not need to drain the entire cooling system. If you are replacing the very expensive heater valve now might be a good time to give it a good flush. Please see our article on flushing and replacing your coolant.

Removing the coolant reservoir will give you more room to work. If you would like to remove it please see our article on replacing your coolant overflow reservoir for additional assistance.

The heater valves (red arrow) are located on the right side of the car between the battery and firewall.
Figure 1

The heater valves (red arrow) are located on the right side of the car between the battery and firewall. You can see the main coolant line from the engine and the two lines that run to the heater core (yellow arrows) along with the windshield reservoir heating line (green arrow) in this picture.

Begin by pinching off the coolant hose from the engine or draining the coolant.
Figure 2

Begin by pinching off the coolant hose from the engine or draining the coolant. Even with the line pinched off there will be some coolant that spills, so be prepared for it. On the engine side of the firewall use a flathead screwdriver and remove the clamp then hose from the valve body (red arrows). You can leave the windshield fluid reservoir line attached as it is easier to remove later.

Disconnect the wiring harness from the top of the forward solenoid (red arrow) by squeezing in the clips and pulling it back.
Figure 3

Disconnect the wiring harness from the top of the forward solenoid (red arrow) by squeezing in the clips and pulling it back.

Disconnect the wiring connection (red arrow) from the lower solenoid (yellow arrow) in the same manner as above.
Figure 4

Disconnect the wiring connection (red arrow) from the lower solenoid (yellow arrow) in the same manner as above.

Next disconnect and remove the battery.
Figure 5

Next disconnect and remove the battery. Please see our article on battery replacement for additional assistance. With the battery removed use a 10mm socket and remove the two bolts holding the tray in place (red arrows) Pull the tray up and out.

With the tray removed you can see the two heater core lines (yellow arrows) connected to the heater valve (red arrow).
Figure 6

With the tray removed you can see the two heater core lines (yellow arrows) connected to the heater valve (red arrow). It is a good idea to clean all the dirt and debris you will find under the tray (green arrow).

Pinch off the two heater core lines and use a flathead screwdriver to remove the hose and clamps on the lines.
Figure 7

Pinch off the two heater core lines and use a flathead screwdriver to remove the hose and clamps on the lines. Separate the lines from the heater valve (green arrows). Even with the lines pinched off there will be some coolant that spills.

If you are replacing the heater core hoses, they attach to the core by standard hose clamps.
Figure 8

If you are replacing the heater core hoses, they attach to the core by standard hose clamps. It is a tight fit but use a small flathead screwdriver and remove the clamps and hoses (red arrows).

There are three rubber grommets that sit in cut outs in the heater mount (yellow arrow, one shown).
Figure 9

There are three rubber grommets that sit in cut outs in the heater mount (yellow arrow, one shown). Slide the rubber grommets (red arrow, one shown) out of the cut-outs. The valve is now free.

Pull the valve back out from the grommet in the firewall (yellow arrow).
Figure 10

Pull the valve back out from the grommet in the firewall (yellow arrow). Turn the valves on their sides and remove the hose and clamp to the windshield fluid heater (red arrow).

This picture illustrates the heater valve out of the vehicle.
Figure 11

This picture illustrates the heater valve out of the vehicle. You can see the heater connections for the heater core hoses (green arrows), coolant hose to the water pump (red arrow) and the windshield reservoir heater hose (yellow arrow). Installation is the reverse of removal.

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Comments and Suggestions:
Dray Comments: Hey there, I wasn't getting any heat to my system with the temperature turned fully up and the fans on max in my 1991 300ce. I tested the heater valve and found it to be faulty, so I used your instructions to change out my heater control valve with a newly tested replacement. Thanks to your article it went smoothly. However, after installing the new heater control valve I still wasn't getting any heat. The new valve tested good but still no heat at normal operating tempertures, just cold air. The hoses running to the valve from the water pump/engine are hot, the two hoses from the valve are hot, but right before the one hose connects to what I believe is the metal heater core line going into the cabin, it gets cool like the coolant is not running any further. Does this sound familiar to anyone and can someone point me in the right direction. Thank you sooo much for these tech articles.
September 10, 2015
  Followup from the Pelican Staff: Coolant to the valve, but not through it? See if you can manually activate the valve, confirm coolant flows through the heater core. - Nick at Pelican Parts  
quest1966 Comments: My pleasure. I don't know if you can answer this but I have a question about that valve. I am planning to do a thorough flush of the coolant system. Rather than running everything through the block and radiator drain. I would like to flush the heating system directly running water from the driver side line to the heater core and detaching the hose on the heater return line under that heater valve. The question - does the flow from the windshield washer heater through the valve stay open at all times? If not, will it open if the heater is on? Thank you!
May 1, 2015
  Followup from the Pelican Staff: Good question. I believe it runs through the washer fluid all the time. - Nick at Pelican Parts  
quest1966 Comments: In Figure 11, the red arrow connection is identified as, "input coolant hose from the engine." Correct me if I'm wrong but I believe that connection is the return to the water pump.
April 29, 2015
  Followup from the Pelican Staff: You are correct sir! I will have the article updated.

Thanks for catching that. Feedback likes this just makes the articles better. - Nick at Pelican Parts
 

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