According to learned advisors, my temperature control problem on my '85 300SD may be caused by a problem with the "in-car temperature sensor", which supposedly is located on the dash, either adjacent to the right speaker or behind a small grill in the center of the dashboard. Does anyone know where it actually is? I have been over that damn dashboard and can't see anything remotely looking like a "small grill", etc. Many thanks for your help.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

It appears to be on the ceiling of my car above the rear-view mirror.

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VR
1967 250SL

Check out this link. http://www.mbca.org/MBCA_Troubleshooting_cruise_cont.htm

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

Thank you! I never thought to look up there. Now if that only is the cause of the problem...... Thanks again!

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

What is the temperature control problem?

Thanks for asking. The car warms up fine, and when driving on the freeway with the EC button chosen and no fan, I get little or no heat no matter the setting. If I turn the car off , then on immediately, I get a decent amount of heat with no fan, but if I turn the blower on, either high or automatic, the heat dissipates quickly. I ran a resistance test on the sensor and it is o.k. and the suction blower now pulls air past it. When I have heat available, if I pull the connector to the monovalve, I get no heat - which I was told is the test for the monovalve's proper operation. Frankly, I am beginning to think I have a problem with the recirculation pump not running, but that is so buried it is almost not worth it to fix the damn thing. Any fis or testing suggestions will be warmly welcomed!

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

Ron, it sounds like you have a coolant circulation problem, not a temperature control problem. The suction blower in my late '85 stopped turning and I'd ROAST until the cabin heated up the sensor and turned the heat down.

Since you've checked the sensor and the monovalve, that probably leaves the circulation pump. The rest of the gang here can probably give you the hot tip on checking and replacing it.

I'd replace it, because your 300SD isn't even broken in yet and you'll have it around for quite a while to enjoy the heat. Good luck.

BTW, I STILL miss the old '85!

BCingU, Jim

Ron,
Before you eliminate the mono valve as the cause of your problem, take it apart and inspect it. If the diaphram is torn, it needs to be replaced, as antifreeze gets behind the solenoid and causes a hydrostatic lock. This keeps the valve closed when it should be open. Your symptoms are typical for this problem. Hope this helps.
Dan