inadequate floor heat - PeachParts Mercedes-Benz Forum

woolf · #1 01-14-2009, 02:36 PM

This problem with my '85 280SL has had me confused for the last couple of months

I get good heat out of the screen vents, so-so heat of the dash vents, but barely any heat of the floor vents.
I removed the lower dash panels and could see that the flaps appear to move to the correct positions, and plenty of air blows out of the vents when I select them.

The heater valve opens ok, and I've flushed the cooling system just to be sure, but I guess that side of things must be ok otherwise I wouldn't be getting hot air on the screen.

Any suggestions welcomed - I'm getting tired of numb feet

JimFreeh · #2 01-15-2009, 06:29 AM

Quote:

Originally Posted by woolf

This problem with my '85 280SL has had me confused for the last couple of months

I get good heat out of the screen vents, so-so heat of the dash vents, but barely any heat of the floor vents.
I removed the lower dash panels and could see that the flaps appear to move to the correct positions, and plenty of air blows out of the vents when I select them.

The heater valve opens ok, and I've flushed the cooling system just to be sure, but I guess that side of things must be ok otherwise I wouldn't be getting hot air on the screen.

Any suggestions welcomed - I'm getting tired of numb feet

Do you have the semi manual temp control?

Left and right temp select and two ratary knobs, left for fan and right for vent select?

If so, sounds like a vacuum failure.

But I'm a bit confused by your description. Are you saying you get lots of cold air out the floor vents at the same time you get heat out of the defroster? This doesn't make sense, as the core supplies heat, then the airstream is routed to the various outlets. Other than the center vents (which do not get heat), the other vent openings (defrost, floor and outside dash vents) are all supplied with air that has been through the heater core first.

Again, sounds like you have no vacuum to your floor ducts, or the pod has failed.

Jim

woolf · #3 01-15-2009, 07:36 AM

Hi Jim

Thanks for the reply, my controls are different than you describe, there are 2 pairs of vertical sliders, and just one rotary knob which controls the fan.

I agree it sounds impossible, but I really do have hot air out of the defrosters and cool air out of the floor vents

JimFreeh · #4 01-15-2009, 08:52 AM

Quote:

Originally Posted by woolf

Hi Jim

Thanks for the reply, my controls are different than you describe, there are 2 pairs of vertical sliders, and just one rotary knob which controls the fan.

I agree it sounds impossible, but I really do have hot air out of the defrosters and cool air out of the floor vents

That sounds like the early style, usually found in pre 77 or so USA versions. Not too familar with that system, yet.

I'm surprised it was still being used on an 85.

Jim

woolf · #5 01-16-2009, 02:42 PM

Quote:

Originally Posted by JimFreeh

That sounds like the early style, usually found in pre 77 or so USA versions. Not too familar with that system, yet.

I'm surprised it was still being used on an 85.

Jim

Ok thanks anyway Jim, I'm just trying to avoid having to perform exploratory surgery.

John

ctaylor738 · #6 01-17-2009, 09:53 PM

I found this on Benzworld a while ago. It's a typically chatty thread, but there are some diagrams that may help with your problem.

http://www.benzworld.org/forums/r-c107-sl-slc-class/1376021-vacuum-diagram-needed-3.html

woolf · #7 01-18-2009, 03:34 PM

Quote:

Originally Posted by ctaylor738

I found this on Benzworld a while ago. It's a typically chatty thread, but there are some diagrams that may help with your problem.

http://www.benzworld.org/forums/r-c107-sl-slc-class/1376021-vacuum-diagram-needed-3.html

Thanks Chuck, can't say i've ever noticed any vacuum elements around my heater so I'll have another look. It hadn't occurred to me to search for vacuum diagrams

coleyjf · #8 01-19-2009, 02:18 AM

Hi Woolf

Your heater controls sound like my 88 UK ( Euro) - Is yours a Euro model perhaps?

Inside is like this:

(Sorry but the R/H control is partly hidden by the wheel and you may not have the "head light elevation control" as I don't think that's leagal in the US

Obviously it's all "the wrong way round" in your case!!!

Cheers

Jim

woolf · #9 01-19-2009, 03:06 AM

Hi Jim

Yes that's the same layout as mine (including the steering wheel

), so I guess this type must be fitted to the later Euro models.

Mine has air-con (not climate control) as well but I doubt it makes much difference to the airbox controls.

coleyjf · #10 01-20-2009, 02:37 AM

Hi Woolf

Mine's a facelifted (86-89) Euro (UK) spec 300SL so I would expect the 280 to be a very similar beast and of course being in the US you've got Air Con. My heating is VERY EFFICIENT in the foot well so as It's probably the same system I'll have a look later today and see if I can spot any areas you might look at. As I've never had a prob with the heating it's an area I've never investigated!

Cheers

Jim

woolf · #11 03-21-2009, 06:44 PM

Update - problem found and mostly fixed.

I had a good look behing the glovebox and behind the instrument panel and found that the floor heat flaps had jammed both sides, causing the operating levers to disconnect. It felt as though they were going slightly too far (over centre) and it took at lot of wiggling to get them back in position. I then adjusted the operating lever so that it couldn't throw the flap as far and now I have one side working well.
Unfortunately I had already managed to break the flap internally on the driver side by pushing the lever too hard last year so that will have to stay as it is, although I have temporarily bodged it by making a hole in the side of the heater box and pushing the flap into the position I want and sealing it there for now.