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Replacing Your Mercedes Benz Heater Core
 
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Pelican Technical Article:

Replacing Your Mercedes Benz Heater Core

Steve Vernon

Time:

4 hours4 hrs

Tab:

$120

Talent:

***

Tools:

8mm, 10mm and 13mm socket and wrench, screwdrivers, small needle-nose pliers, rags

Applicable Models:

 
Mercedes-Benz 190E (1984-93)
Mercedes-Benz W124 (1986-95)
Mercedes-Benz W126 (1981-91)

Hot Tip:

Take lots of pictures.

Performance Gain:

Working heat

Complementary Modification:

Replace your coolant

Mercedes-Benz W201 models are known to eventually have problems with their heater boxes, or more specifically, they usually need to have the heater core replaced. If you are in need of a new heater core you will need to remove the heater box to perform this work. While this job does not need any special tools or even any special talents, it is time consuming, and can be very nerve racking (as you are going to be taking most of the cars controls out). It can easily be done by a DIY mechanic if you take your time, follow the instructions and take lots of pictures to help you put it all back together. Keeping the fasteners for each area in Ziploc freezer bags (the kind you can write on) will reduce confusion, assembly errors, and some of the nervous stress, especially if the job stretches over days or weeks.

There is a fair amount of work that needs to be done before you can remove the heater box, and due to the length of this article I am going to refer you to our other articles to get you to this point; this article will only cover removing the heater box and replacing the core.

First you will need to remove your instrument cluster, please see our Pelican Parts Technical Article on Removing Your Instrument Cluster for more information.

Next, you will need to remove the center console, please our Pelican Parts Technical Article on Removing Your Center Console for more information.

Next you will need to remove the dash, please see our Pelican Parts Technical Article on Removing Your Dashboard for more information.

To replace the heater core you will need to remove the heater box from the car. There are two coolant lines connecting the heater core to the engine coolant system. If your heater core has already failed or split you probably have coolant all over the interior of your car, if it has not, it is important to get as much coolant out of the lines and core as possible to keep it from spilling inside the vehicle.

You are going to be working with the coolant so make sure the vehicle is cold. Begin by safely draining the coolant, and then place a large catch pan under the engine. Disconnecting the heater hose that runs from the rear of the head on the driver side, it is located behind the last intake runner and beside the oil filter.

Loosen the clamp and remove the return hose by the recirculation pump. Coolant will spill out so be ready for it.

You are now going to try and evacuate all of the coolant in the lines and the heater core by using compressed air. You do not need a lot of pressure, twenty pounds should be fine. I used an extra ball joint seal over the air nozzle to help seal the hose and put the compressed air in through the return line. Be careful as the coolant will come out of the other hose with a fair amount of force and speed. Once you have gotten as much coolant as possible from the system move to the interior of the vehicle. You can also use a shopvac to suck (through the tubes) any coolant remaining in the heater core.

Remove the vacuum line from the vacuum element on the top of the heater box.

Disconnect the wiring harness located on the passenger side of the heater box by the return tube.

Lift the passenger side plastic air duct up and out.

Wiggle the wiring harness out from the top driver side of the heater box, and cut the plastic wrap holding the wiring loom.

Working in the driver side foot well, pry and slide the plastic clip on the heater line back from the grommet where it passes through the bulkhead. Remove the two 8mm bolts holding the metal heat line going into the heater core. Loosen the 10mm nut that holds the heater box to the bulkhead. You will need to pull the heater line from the core. Gently wiggle it back and forth while pulling it straight out.

Separate the two vacuum lines from the vacuum element on the heater box by the speedometer cable.

Behind where the center console was and under the heater box are three vacuum lines connected to pink vacuum elements. Take pictures or label the lines for reassembly and then separate the lines form the units.

Move to the passenger side of the heater box and remove the two 8mm bolts holding the return heater line to the core. Pull the line straight back while wiggling gentle.

With the line disconnected loosen the 10mm nut holding the heater box to the lower bulkhead below the return line.

Move to the top of the heater box and remove the two 10mm nuts holding the box to the bulkhead.

Slide the driver side air distributor from the box.

You can now lift the heater box up and out of the car. To get the core out of the heater box you will need to disassemble the box. Flip the box over so you can see the internal flaps. Remove the three Phillips-head screws. Remove the cover over the vacuum unit attached to the flap for the defroster on the driver side of the box. Place a flathead screw driver on the shaft of the left hand defroster and pull the vacuum nozzle away from the flap while pushing down on the shaft with the screw driver. This will disengage the nozzle from the shaft. Remove the three clips on the top of the box along with the clips on the defroster shafts, and the lower heat distribution channels. Remove the lower unit along with the vacuum pod and metal control rod. Remove all the remaining clips on the box. Flip the box over so you can see the core and remove the six Phillips-head screws on the plastic piece over the core. Separate the plastic cover and remove the core from the housing. There are four small, square nuts that sit in the plastic ends of the heater core that hold the bolts from the coolant lines in place. They are held in place by the housing and will fall out when you remove the core. Note: Make sure you reinstall these before putting the heater box back together! If you forget you will need to disassemble the unit and start the assembly over again, as there is no way to install them once the core is in the housing and the heater will leak like a sieve without them!

Use new padding between the core and housing to help insulate it from heat and vibrations.

Installation is the reverse of removal.

This photo shows the heater box installed to the bulkhead of the car.
Figure 1

This photo shows the heater box installed to the bulkhead of the car. The entire heater box has to come out to replace the heater core.

After draining the coolant from a cool vehicle, use a flat head screw driver and disconnecting the heater hose (green arrow) that runs from the rear of the head on the driver side, it is located behind the last intake runner and beside the oil filter.
Figure 2

After draining the coolant from a cool vehicle, use a flat head screw driver and disconnecting the heater hose (green arrow) that runs from the rear of the head on the driver side, it is located behind the last intake runner and beside the oil filter.

Using a flathead screw driver, loosen the clamp and remove the return hose (green arrow) by the recirculation pump.
Figure 3

Using a flathead screw driver, loosen the clamp and remove the return hose (green arrow) by the recirculation pump. Coolant will spill out so be ready for it.

Use compressed air (around 20 pounds is fine) on the return line (red arrow) and blow all the coolant out of the heater core and lines.
Figure 4

Use compressed air (around 20 pounds is fine) on the return line (red arrow) and blow all the coolant out of the heater core and lines. You can also use a shopvac to suck out any coolant remaining in the heater core.

Remove the vacuum line (red arrow) from the vacuum element on the top of the heater box.
Figure 5

Remove the vacuum line (red arrow) from the vacuum element on the top of the heater box.

Disconnect the wiring harness (yellow arrow) located on the passenger side of the heater box by the return tube.
Figure 6

Disconnect the wiring harness (yellow arrow) located on the passenger side of the heater box by the return tube.

Lift the passenger side plastic air duct up and out.
Figure 7

Lift the passenger side plastic air duct up and out.

Wiggle the wiring harness out from the top driver side of the heater box (red arrow), and cut the plastic wrap holding the wiring loom (green arrow).
Figure 8

Wiggle the wiring harness out from the top driver side of the heater box (red arrow), and cut the plastic wrap holding the wiring loom (green arrow).

Working in the driver side foot well pry and slide the plastic clip (red arrow) on the heater line back from the grommet where it passes through the bulkhead.
Figure 9

Working in the driver side foot well pry and slide the plastic clip (red arrow) on the heater line back from the grommet where it passes through the bulkhead. Remove the two 8mm blots (green arrows) holding the metal heat line going into the heater core. Loosen the 10mm nut (yellow arrow) that holds the heater box to the bulkhead. You will need to pull the heater line from the core. Gently wiggle it back and forth while pulling it straight out.

Separate the two vacuum lines (green arrows) from the vacuum element on the heater box by the speedometer cable.
Figure 10

Separate the two vacuum lines (green arrows) from the vacuum element on the heater box by the speedometer cable.

Behind where the center console was and under the heater box are three vacuum lines connected to pink vacuum elements (red arrow).
Figure 11

Behind where the center console was and under the heater box are three vacuum lines connected to pink vacuum elements (red arrow). Take pictures or label the lines for reassembly and then separate the lines from the units.

Move to the passenger side of the heater box and remove the two 8mm bolts (yellow arrows) holding the return heater line to the core.
Figure 12

Move to the passenger side of the heater box and remove the two 8mm bolts (yellow arrows) holding the return heater line to the core. Pull the line straight back while wiggling gentle.

With the line disconnected loosen the 10mm nut (yellow arrow) holding the heater box to the lower bulkhead below the return line.
Figure 13

With the line disconnected loosen the 10mm nut (yellow arrow) holding the heater box to the lower bulkhead below the return line.

Move to the top of the heater box and remove the two 10mm nuts (green arrows) holding the box to the bulkhead.
Figure 14

Move to the top of the heater box and remove the two 10mm nuts (green arrows) holding the box to the bulkhead.

Slide the driver side air distributor (green arrow) from the box.
Figure 15

Slide the driver side air distributor (green arrow) from the box. You can now lift the heater box up and off its mounts (red arrow) and out of the car.

Pull the heater box clear of the fire wall and take it to your bench to remove the core.
Figure 16

Pull the heater box clear of the fire wall and take it to your bench to remove the core.

This picture shows the air conditioning condenser in the fire wall.
Figure 17

This picture shows the air conditioning condenser in the fire wall. This is not the heater core and you do not need to remove this.

This photo illustrates the heater box.
Figure 18

This photo illustrates the heater box. You will need to take this apart to replace the core as it is contained inside the housing.

Flip the box over so you can see the internal flaps.
Figure 19

Flip the box over so you can see the internal flaps. Remove the three Phillips-head screws.

Remove the cover over the vacuum unit attached to the flap for the defroster on the driver side of the box.
Figure 20

Remove the cover over the vacuum unit attached to the flap for the defroster on the driver side of the box. It is held in place by two plastic clips inside by the flaps.

Place a flathead screw driver on the shaft of the left hand defroster and pull the vacuum nozzle away from the pushing down on the shaft with the screw driver.
Figure 21

Place a flathead screw driver on the shaft of the left hand defroster and pull the vacuum nozzle away from the pushing down on the shaft with the screw driver. This will disengage the nozzle from the shaft.

Remove the three clips on the top of the box along with the clips on the defroster shafts.
Figure 22

Remove the three clips on the top of the box along with the clips on the defroster shafts.

Remove the clips from the lower heat distribution channels.
Figure 23

Remove the clips from the lower heat distribution channels.

Remove the lower unit along with the vacuum pod and metal control rod.
Figure 24

Remove the lower unit along with the vacuum pod and metal control rod.

Remove all the remaining clips on the box.
Figure 25

Remove all the remaining clips on the box.

Flip the box over so you can see the core and remove the six Phillips-head screws on the plastic piece over the core.
Figure 26

Flip the box over so you can see the core and remove the six Phillips-head screws on the plastic piece over the core.

Separate the plastic cover and remove the core from the housing.
Figure 27

Separate the plastic cover and remove the core from the housing.

There are four small, square nuts that sit in the plastic ends of the heater core (red arrow) that hold the bolts from the coolant lines in place.
Figure 28

There are four small, square nuts that sit in the plastic ends of the heater core (red arrow) that hold the bolts from the coolant lines in place. They are held in place by the housing and will fall out when you remove the core. Note: Make sure you reinstall these before putting the heater box back together! If you forget you will need to start assembly over again as there is no way to install them once the core is in the housing and the heater will leak like a sieve with out them! Use new padding between the core and housing to help insulate it from heat and vibrations.

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Comments and Suggestions:
willydefender Comments: Pelican, What other parts should be tested or replaced while the dash board is torn apart? What do you recommend?
September 29, 2016
  Followup from the Pelican Staff: Just the heater core, maybe the evaporator. - Nick at Pelican Parts  
DanaR Comments: I am wondering what is going on with my hoses here?? Is this a possible bypass to replacing the heater core? I also have no heat, blows cold air. But I am wondering where that hose is supposed to go?
April 10, 2016
  Followup from the Pelican Staff: Looks like the heater core has been bypassed. You are likely missing hoses and a connector. 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
 
EuroClassics Comments: I plan on performing this tedious job on a 92 2.6. Do I just reverse the order of taking it apart in order to put it back together?
January 19, 2016
  Followup from the Pelican Staff: Yes take notes of item and wiring positions to help with reassembly. - Nick at Pelican Parts  
rairden Comments: 1987 190E. 227,000 mi. Heater core blew last May. Exciting hot-foot and steam bath. Been driving since then with hoses clamped off. California isn't too cold. Last week I finally got up the nerve to attack the dashboard, instrument cluster, center console, etc, with invaluable help from these great tech articles. Still was a mess, and fairly destructive. Lots of broken plastic tabs, but nothing fatal. Worked a little each day, finally got the core out of the heater box tonight, and yes it seems to have blown the seal at one end. Just now ordered a Behr replacement core, says Friday 13th delivery. Gonna be a long weekend trying to put everything back together.
February 11, 2015
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
cmar Comments: 1993 190e with a/c/heat issue. when the push button climate control is pushed for redirection of air flowother then defrost, that the only part workingthe unit sounds like it is over loaded and you here a ping sound.bi-metallic thermal overload tripping the unit is a year old and just replaced the mix air flap potentiometer/relay, depends on the service manual you are reading. I understand the compressor cutout control unit may be at fault or the vent flap switch over valve. many major parts of this system are new,, any insight would be greatly appreciated. polar vortex and we are freezing in this car. thank you, cmar
January 8, 2015
  Followup from the Pelican Staff: If you hear a noise in the instrument panel, I am not sure if the compressor would be at fault. You could have a broken flap in the heater box, causing a motor to over-extend. - Nick at Pelican Parts  
vince Comments: from pictures provided and instruction, i did not read or did not see anything about heater control valve and vacuum element. will i need to do all these steps to get to the heater control valve with vacuum element in order to replace it? if possible pics with steps. thank you for your time and your products are awesome.
January 23, 2014
  Followup from the Pelican Staff: No, those items are separate from the heater core. If we get a chance to perform that repair, we will create a tech article. We currently do not have instructions for it. - Nick at Pelican Parts  
Mike Comments: would it be a good time to remove and install a new air conditioner condenser at this time? I have a 1986 model.
November 28, 2013
  Followup from the Pelican Staff: The condensor is mounted in front of the radiator. You might mean the evaporator. It would be if you have the tools to discharge the and recharge the system. Evaps always seem to leak and this will save you having to go back in there. - Nick at Pelican Parts  

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