Main.TrailIndexPage | Electrical Systems | Electrical.Heating

Heating system


The Heating (German: Heizung) system is part of the Cooling, heating and air-conditioning systems in the car. The heater is not as effective compared with a modern car... The heat works best if you have the fresh air lever (top left) in about the middle position, not off.

For historic reasons (don't ask) the heating system is described in the Electrical Systems section of the Technical Manual, and it is too much hassle to move it elsewhere.




The heater effect can be improved by:

1. Making sure that the engine is running at the correct operating temperature. Install a 190F (85C) thermostat if necessary.

2. Remove the rubber plug at the top of the firewall and make sure the lever on the heater valve is at the full-on position. Adjust or fix the cable and/or R&R the valve if necessary.

3. Clean or replace the air filter at the bottom of the cowl air intake.

Old Yahoo content

The following is the content from the old Yahoo documents on the site. It needs to be structured and edited in the correct sections of the entire document. After moving particular content to its correct place in the manual, please delete it here.

The heater core is removed from under the dashboard.

  1. In order to remove the heater core it is necessary to remove the heater blower motor. While I had it out I found a local shop which rebuilt the motor by replacing the bushings and bearings. The local shop also rebuilt the blower motor for my air conditioning unit.

I went over a few good bumps and it sounded like something let go inside the dash, banging metal sound. I narrowed it down to heater box, removed (from inside) and found a 16 inch by @3inch pice of flat metal (says buhr), there are three small holes on each end and it has insulation glued to it. I think it probably came apart from the scoop in front of the front window and then fell down into the heater box. All of my controls operate (and function) correctly, can anyone ID where it came from before I take the scoop off? The side with the insulation is black and the other side is metal (looks galvanized).

My mis-spelling, it says Behr. I was able to get it out by removing the right side plastic cover of the air control box. It was resting in the box and against the heater core, appears to have fallen from the scoop area. Maybe its a backing plate for the fresh air flap?, it's about that size.

Oh yeah now I see where it came from (imagining a 3d image in my head). That is one of the side plates used to attache to the heater matrix core, the three holes on each end are for the rivets to hold together the shield for the matrix. Can you picture the heater matrix inside the plastic housing for the heater box? Ok, now picture a smaller metal box immediately surrounding the heater matrix itself on all sides but two large flat sides where the air passes through within that bigger plastic box, and there you have it. The mystery is solved, and if you are worried about it missing from there, you won't notice any effect other than the slight drop in the full heat temperature coming out the vents, as the air passing through is not as concentrated as before.

If you get involved in replacing the mysterious metal part be careful. The side plate to the heater core is not riveted on. The hoiles are solder points. Mine came off and I had it soldered back on when I had the heater core out.

It does say BEHR, I do have AC but it is the Kuhlmeister. Per advisement, I surely will leave it out till my heater core bites the dust! Everything functions perfectly without it so why look for trouble! You can diagnose this problem by rapping on the underside of the heater box fan (metal section resting on tranny tunnel), you will hear metal banging around (kind of tinny sounding when banging with hand), but when driving it sounds like the noise generates from the back of the gauges!

If the air coming into the cabin through the small side vents, the top edge of the dashboard and below the dash (i.e. all air outlets other than the louvred fresh-air vents) is very warm/hot despite having the two slide controls in the "cool" position, then there is likely something wrong with the warm water shutoff valve located just below the rubber grommet just under the hood, at the base of the cowl air box. In short, the temp slide controls each operate one flap that is located right below the chrome-louvred air intake cowl. When the control is set to "hot" (red) then the flaps channel air via the heater core (if I understand the operation correctly). The driver's side lever also operates a hot water valve located on top of the heater core, through a short linkage that is very similar to all of those gas linkages in the engine bay. This valve, which controls the amount of hot water from the cooling circuit to the heater core can seize, and the slide lever on my car was for this reason disattached by a previous owner. Instead, he/she put a manual valve in the hot water line right in front of the firewall under the hood, and this allows me to manually control the amount of hot water (from zero to max). The sliding controls in the dash do the rest by controlling the amount of air that is heated by the core. I suggest you check out the operation of the flaps and the valve, all located below the air intake cowl. In order to access the valve you (should) need to remove a large circular rubber grommet. If the valve is seized or will not close all the way, you will have warm to hot air even if the slide controls are set to "cool". If the valve is in fact seized, and you do not immediately want to remove the heater core to have this fixed, I can recommend the "external" valve solution as applied on my car. It works fine, only drawback is you have to open the hood to close/open the valve, but then again you typically only do this a few times a year maximum. I guess it is also possible that the slide controls do not actually attach properly to the flaps. While you are at it, you can also check whether the water drainage holes are clear (in the outer corners, see also recent post on suggested spring cleaning activities here) and whether the 'main flap' (the one that allows any air into the interior to begin with, also located in the intake cowl box) has its rubber gasket intact. I found mine to be brittle and I replaced it with a new one.

Heat shield under passenger floor? I am having a problem with heat (enough to smoke my new carpet), caused by the pipes that run below the floor. The pipes are in the right position and the fuel and air mixture is correct it seems, but the temp about 1ft. back from the last bend is great enough to blister the undercoating off. I don't have a heat shield and don't see that one is missing. Did all 250sl's have this item? I have a temporary shield in place and it works wonders (muffler repair pad). If I create a real shield from bent metal should it mount to the floor or pipes?

My heater fan sounds like it's dying. Any advice? Is it as miserable/impossible to replace as the 108? If so, FUGEDDABOUTIT! Also, I need the rear axle ratio & understand it's stamped on the axle. But that involves a lot of greasy/ dirty/ poorly lit/ hard to get to territory. So if anyone could provide a more specific location it would really help.

To answer your question .... MB basically built the rest of the car around the heater motor. Plan on one difficult job.

Having been in the heater fan neighborhood last weekend (I even went so far as to rebuild the existing motor). It isn't a terrible job but it does require a fair bit of patience. I guess the big hint is to have some foam tape on hand to replace the seals that will be deteriorated with age. Also the bracket that holds the lower center of the fan housing has to come out and is thru bolted to the tunnel, which means that you have to access the nut by peeling back the carpet on the right side of the trans tunnel and removing the access plate on the side of the tunnel. Once I got the housing out I removed the side covers and removed the fan wheels(be sure to mark them as to rotation and hand). I removed the set screws from the inside of the fan wheels and used a pair of locking pliers (Vise Grips) on the shaft and one on the outside of the fan wheel hub to break them loose.
< Cigar Lighter | Main.TrailIndexPage | Electrical.Blower >