'89 230 TE Heater - Cold Middle Vent
 

i have an '89 230TE, this is a european car. the climate control is a bit of a mystery since i have no info in my factory manuals on this particular system. i'm having a bit of trouble finding documentation on this system. the controls have two temp wheels and two rotary switches, so it's completely different than the north american ACC controls. this car does not have air conditioning. i have done some web research on a UK MB site which is helping a bit, maybe there's more help here...

so far here's what i have:

heat works on floor and outer vents. thermostat seems fine, operating temps are fine. centre vent blows cold regardless of temp wheel settings.

on the duo valve i have both outlet hoses to heater core hot. as i understand the system, the core is split in two and the centre vents are off one half of the core, the other vents off the other part of the core. is this correct?

so with the symptoms i have now it's possible that the part of the core that is for the centre vents is blocked. it just seems unlikely that these vents would blow dead cold while the other vents are nice and hot.

any ideas on next steps to take?

Centre vents are for fresh air and air conditioning.
Heat does not come from the centre vents - that's the design.

Scott, close the center vent for the Winter. It's that simple.

those 2 center vent only work when the ac setting is set to economy,plus is you believe heat shoukd be coming from them check underhood to see is you have an auxilliary water pump,if its not working it does not blow hot coolany up into the dash board.

Center vent only blows unheated air.

When you set the controls for heat, there is a vacuum damper that should close off the center vent on a W124 car.

The easy solution is to simply move the manual thumbwheel on the vent to the closed position....

Jim

thanks for the replies.

there is some confusion still. first of all, this car has no A/C. i realize the center vent on an A/C equipped car will not blow hot air, only cold. on my '87TD for instance, the centre vent will never blow cold air unless the A/C is on, ie the thumb wheel setting is lower than the ambient temperature. the climate control system on this car is quite a bit different.

as far as simply closing the vent, yes that works reasonably well to shut off cold air flow to the inside of the car. it will still leak a fair bit of air. i had thought of removing the vent and putting some insulation in the duct so no air can pass, this will work fine. but to me it still seems like there is something wrong with the way the system is working at the moment.

so on my euro car, the vacuum pot for the center vent is still there, like on my '87TD. this makes the most sense, that when you select heat the vacuum actuator should close off the center duct. it doesn't make any sense to me that the air regulating thumbwheel on the vent grille would be solely responsible for closing off cold air supply to the cabin. in our climate the outside air is very cold at this time of year and with the way the system is behaving now, you get a lot of cold air even with the grille thumb wheel closed off, especially if the fan is on one of the high settings.

Over the 20 year plus period the seals deteriorate and let a bit of excess air through.
If you live in a warmer climate this is exacerbated because warm leaks out when you don't want it.
The seals in my car are fine. When turning the central wheel to seal off the centre vents they are sealed up tight.

In my Euro W124 AC cool air is emitted from the centre vents whether or not the air circulation is closed to interior or fresh air.

what do you mean by 'air circulation'?

The re-circulation air switch.
Unfortunately you don't have it in your car - only in A.C. models
Here's your car - probably
http://farm6.static.flickr.com/5044/...5ecdb1a9_z.jpg
http://farm6.static.flickr.com/5203/...68288031_z.jpg
http://farm6.static.flickr.com/5203/...26d59d4c_z.jpg

correct, no re-circulation switch on my car.

also, correct on the diagrams, yes those are super helpful and exactly what i need, thanks.