1990 300TE blows hot and cold air simultaneously

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Tom Sharples - 12 Mar 2005 01:51 GMT

Hi, my 1990 300TE after some amount of normal AC operation, will suddenly
start to blow hot air at the same time as the cold air. This happens at
random times regardless of the setting of the temperature wheel or push
buttons. I've taken the control box out and cleaned and resoldered any
suspicious connections- didn't help. Any suggestions or pointers would be
very much appreciated- thanks!

Tom Sharples

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Tiger - 12 Mar 2005 05:07 GMT

I suggest you use a can of air to blow clean the air intake sensor for
climate control system... where there is a cabin temp sensor... should be on
the top ceiling... near the middle... small cube with fins...

Sometime dust settle there and block passage for accurate reading.

Another source of your problem could be the climate control unit itself.

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crgill@aol.com - 12 Mar 2005 18:45 GMT

Sounds to me like the valve that controls hot water flow into the heat
radiator under the dash is leaking. This would cause exactly the
symptom you describe. The valve is mounted on the inside of the
firewall above the battery, on the passenger side of the car, costs
around $100, and is fairly easy to swap out.

Chris

> Hi, my 1990 300TE after some amount of normal AC operation, will suddenly
> start to blow hot air at the same time as the cold air. This happens at
[quoted text clipped - 4 lines]
>
> Tom Sharples

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pool man - 13 Mar 2005 04:24 GMT

if it has a mono like my 82SD then unscrew the 2 screws that hold the
top on.
pull the magnet out and look for ANY rips in the rubber.

if it has leaked at ant time it will bind it up.
i just got the new valve and replaced it.
i know of people that get a new valve and put the guts from the new one
in the old one for fear of breaking ANY of the plastic
crap under the hood.

if you take your time things will come loose <well they did on mine>
if your car doesn't have this valve
OOPS

the case, minus a few cans!

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marlinspike - 17 Mar 2005 19:40 GMT

I have a similar problem (turn on the heat and I get cold air out of
everything except for the upper side vents on my W126 - even the center
vents open to put out cold air - but replacing the monovalve and cleanign
the temp sensor did nothing for me. I'd be interested in hearing the
solution.
Richard

> Sounds to me like the valve that controls hot water flow into the heat
> radiator under the dash is leaking. This would cause exactly the
[quoted text clipped - 17 lines]
>>
>> Tom Sharples

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