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  #1  
Old 03-01-2004, 07:00 PM
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Posts: 187
Heater suddenly won't blow warm air

HELP!! PLEASE!!

I've never had problem with my 450 sEL W116 '77, with MANUAL a/c and heater controls (euro model). It has always quickly blown almost red hot air when I wanted it to.

All of a sudden, tonight, even with heater 'bars' in the total up position, no heating whatsoever. All hoses seem fine. It woked as usual this morning. Blower works fine. Temp guage in usual position.

But it blows non-heated air. I hadn't even a clue that this would happen. No slow diminution of heat output.

Could this just be a relay? Or fuse? Or because it got warm outside over last few days, it just won't blow hot until outside air gets cooler? Could heater core just have went like that?

I hope it's something simple.

What can I check for on this manually controlled W116? Where can I start?

Can youg ive me a checklist?

any help will be much appreciated.

Thanks!!

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  #2  
Old 03-01-2004, 07:03 PM
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P.S.:

Oh...forgot to mention:

I don't know if this might have anything to do with it, but I changed my oil (myself) over the weekend.
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Old 03-02-2004, 03:32 PM
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Location: Evansville, Indiana
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Check your coolant level -- if it gets low on that car, you can end up with little or no heater flow.

Also check for a cable popped off the heater valve.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #4  
Old 03-02-2004, 03:45 PM
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Thanks. Update:

Worked just fine and strong this morning. Only seems to blow cooler and not hot when it gets HOT outside, which is when I don't need it. When cold out, blows super hot.

How would you explain this?

PS: no loose hoses and coolant at right level.
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  #5  
Old 03-02-2004, 07:23 PM
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Location: Evansville, Indiana
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Could you have a strange thermostat that cuts off the heater flow along with the bypass flow when it opens?

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #6  
Old 03-02-2004, 08:08 PM
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Peter...I don't know. I'll just keep monitoring the situation. So far, i'm not suffering any. We'll see.

Bob
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Old 03-04-2004, 07:46 AM
mapab
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Re: Heater suddenly won't blow warm air

Quote:
Originally posted by bobboyer5
HELP!! PLEASE!!



All of a sudden, tonight, even with heater 'bars' in the total up position, no heating whatsoever. All hoses seem fine. It woked as usual this morning. Blower works fine. Temp guage in usual position.


Thanks!!
OK, this is a common problem on W116s with manual heater controls. The entry of hot water into the heater matrix (hm) is controlled by a vacuum operated diaphragm in the engine bay on the bulkhead. When either (or both) of the heater levers is at position that's above the bottom, vacuum is either shut off or engaged (can't remember) and hot water travels into the hm. The amount of heat is controlled by air mixers which mix external air with internal air. When you operate the up/down heater levers you control the flaps that do the mixing. In the lowest setting there's a mix of 20% hot and 80% cold air. In the highest it's 100% hot.

To diagnose you really need a vacuum pump. With it you can test the heater valve diaphragm. If it's intact then there's not "enough" vacuum. The problem must lie under the dash. Remove the heater control panel and check that the connections for leaks. What the specs are you will have to check in a manual.

Adam
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Old 03-04-2004, 08:24 AM
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Thanks, Adam. However, I don't think I'm going to mess with the panel removal unless or until lfie is too cold and it becomes uncomfortable for me.

Good job. You know your stuff!!

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