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Car Forum / Mercedes-Benz Cars / October 2005

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84 300SD blowing air, but no heat

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Mia - 24 Oct 2005 15:12 GMT
Hi,

I was wondering whether anyone encountered the following problem: when
the heater is turned on, only the cold air is coming out of the vents.
I noticed sometimes when the car idles, the air gets hot only by the
windshield vent.  Also, the air always gets cold once the car starts
moving and never gets hot again.

Thermostat?  Heater core?  Where?  How?  How much?!

:)

Thanks!

Mia
T.G. Lambach - 24 Oct 2005 17:06 GMT
Is the engine's operating temperature 80 degrees C.?

Are both heater hoses hot?

Your car's heat control valve has a screen. It could be that the valve
or its screen needs a look.

The valve CAN be rebuilt with a kit if that's necessary.

There's an electric auxiliary water pump that runs only between certain
temperatures; it's NOT the problem here.

Alternatively, the climate controller may not be giving the heat valve
the ON signal. Check the fuses before tearing into anything.
T.G. Lambach - 24 Oct 2005 21:36 GMT
Heat control valve is called "the monovalve" .
Henry Kolesnik - 24 Oct 2005 18:50 GMT
check the monovalve insert and solenoid.
Hank
> Hi,
>
[quoted text clipped - 11 lines]
>
> Mia
dynamorph@hotmail.com - 25 Oct 2005 16:20 GMT
I had same problem. Check the monovalve
first, which is easy to remove. Mine had a hole
in the rubber gasket. They are not expensive
at parts.mbz.org.

Jim
mickey - 25 Oct 2005 17:01 GMT
I've the same problem in my 85 but it's intermittent.  I've no idea
where a monovalve may be though :)
Mia - 25 Oct 2005 17:30 GMT
Yeah, where is this monovalve in my car?
Mia - 27 Oct 2005 20:57 GMT
I looked around inside the engine compartment and read my manual ...
Nothing.  I called the mechanic ... He said that because the air is
blowing, and the temp gauge is fine, it can't be anything serious.
Time to get some heat!
Henry Kolesnik - 30 Oct 2005 03:44 GMT
The monovalve is under the hood a liittle off center on the passenger side.
4 screw hold the cap that has the rubber insert.
Hank
>I looked around inside the engine compartment and read my manual ...
> Nothing.  I called the mechanic ... He said that because the air is
> blowing, and the temp gauge is fine, it can't be anything serious.
> Time to get some heat!
Mia - 31 Oct 2005 17:50 GMT
Well, here's a lesson to all of us newbies:

My heater would blow cold air only, guys in this group suggested
replacing the monovalve, I didn't listen, I paid the mechanic $170, the
monovalve really WAS the problem.  I got heat, I am happy, but I wish I
got out of work an hour earlier and figured it all out myself instead
of spending the cash.  Although, I haven't seen my mechanic in 9
months, so I guess it was time ... :)

MJ
 
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