Cabin overheating!

My euro '78 350slc is heating constantly. I've adjusted the few controls I have, but too minimum success. When I lowered all four levers, the heating decreased a little. I don't have an a/c by the way. Any ideas on how I could fix this? Is it possible to disable the heating? I'm not willing to invest any money, if possible. Please help, I'm driving long distances and the heat is not bearable with the windows up.

[mbdoc]

Any R/C 107 car w/o climate control has a vacuum controlled heater valve under the hood. Sounds like the vacuum valve isn't working.

Can I close the heater valve permanently? With a clamp or something? This wouldn't have anything to do with an escaping air sound I hear when letting off the accelerator pedal, would it?

Is someone going to respond?
thanks

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1978 350SLC
250000km

[jeffsr]

Sounds like you have a vacuum leak. If it's as audible as you say, it should be easy to find. This may be your problem. See if you can isolate the source of the hissing noise. Probably a broken vacuum hose or fitting.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE

I'm sorry, I should have mentioned that I had already localized that hissing sound. I managed to alleviate it temporarily half a year ago. It's coming from a round like instrument with a small cylinder on top of it, having about the width of a quarter. It's under the air intake manifold, next to the firewall, close to the throttle lever and spring. There's a small piston in it, I think. It's cover was missing. So I made a cover. I put a penny on it and sealed it with bubble gum. It worked and the hissing quit. I'm not sure though if the heating was malfunctioning at this time. It was winter you know. Now it is hissing again. So if anyone thinks this could be causing my heat problem I'll try to seal it again. The noise doesn't really bother me.
Thanks

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1978 350SLC
250000km

[This message has been edited by Mark Sare (edited 09-29-2000).]

[jeffsr]

This is an older car, so I'm taking a guess here. What you are describing is either a vacuum check valve or a vacuum modulator valve. See if it has any lines running to the vacuum heater valve. It should have a least one coming from a vacuum source. Try and trace the lines. At any rate, whatever it is, it surely sounds broken. Get a shiny new penny and some new gum or try and remove it and get a part number and check whth the parts shop here, or your local, friendly, money grubbing MBZ dealer. Good Luck..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE

Could you give a short description of what this vacuum heater valve looks like? I also don't see how pushing the gas pedal would affect the heating. These are probably two different problems.

I'm not that car fluent, but am I right in the assumption that when the heater valve opens, heat is dissipated into the cabin and when it's closed heat is held in place? So it could be that it's stuck in the open position because it's broken or because this vacuum check valve isn't providing adequate suction. Then is there any way I could manually close this heater valve?


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1978 350SLC
250000km

[jeffsr]

The heater control valve is usually near the firewall. Attached to the heater bypass hose from the water pump or front of the engine. Usually round/cylindrical with a vacuum dashpot on one end. Has a vacuum line which heads towards the heater control system inside the car.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE

[Larry Delor]

I can see how pushing on the gas can affect your heat. When you push on the gas, vacuum levels generally drop...so if a vacuum operated device no longer gets enough vacuum to keep a device shut, (like in a hot water valve or something) it will let it open. Sounds like you should have replaced the broken part you mentioned earlier, instead of jury-rigging it. There's gotta be an MB place somewhere near where you live.

I'll try to jury rig it again and if that doesn't solve the problem I'll just have too go to the dealer . Sadly, whenever I take my car to a MB dealer they always find loads of work to do and in addition to that they offer terrible service. For example, I had severly bent the right front supporting arm on my axle, after hitting a sidewalk. It happened on a a wet cobble stone road. My insurance towed it to a MB dealership. They estimated 12000DM ($6000)damage. So my car was a total loss. I got some money and managed to get the car fixed for 1400DM ($700) at a local mechanic. Now I just have liability insurance. I've experienced this at two different MB dealerships. They are always trying to take advantage of one. On another occasion, for just some routine work, the MB dealership in Hanau scratched up my hood, pretty deep scratches, and totally messed up my after market spoiler, I threatened to sue them, but couldn't prove the hood scratches, just the spoiler. So they repainted it. There are many more stories I could tell. Anyway, I have a strong aversion towards MB dealerships and try to avoid them whenever I can.

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1978 350SLC
250000km

[Larry Delor]

Why don't you see if you can find a part number on that broken piece, or see if you can squeeze the number out of the parts guy at MB. Once you have it, buy it from here, and to heck with that pompous dealership.
-Larry
Do you speak fluent German? Sometimes Dealers get a little hoity-toity with foreigners.

I think a part is actually missing. That part I described above has two hoses running from it, as well as one more hose that leads to nothing. I checked within it's radius and can't find anywhere where it could have possibly been connected. So I took some gum and plugged the hose, now there is no more hissing. The penny-gum cover I made is obviously still sealed. So this hose must've been connected to something before. The car still heats up though.

No, I don't speak fluent German. I'm actually American. Yes, I agree that could be the reason for my treatment, but also because I have an old car.


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1978 350SLC
250000km