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Old 09-05-2004, 12:30 PM
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Climate Control

I'm having serious trouble out of my climate control. Just last month the A/C seemed to quit working. I checked the freon and pressures, all ok. I then noticed that I do not have any control of the temperature. It will not put out heat either, then noticed that the fan will not cut off. Is this a sure sign of the Climate Control Unit. Any help would be appreciated. :
87' 300D Turbo

Last edited by igotdebenz; 09-05-2004 at 12:32 PM. Reason: Car Model
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Old 09-05-2004, 05:16 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,811
I'd investigate the cabin temp sensor before investing in a new push-button unit but lack of blower control does indicate a bad PBU.

95 S420
87 300SDL
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Old 09-06-2004, 10:45 AM
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I'll check the temp sensor to make sure it is working properly. Sure wish there was a way to do minor checks with a multi meter. All books I have, show that you have to have the Impulse Counter to determine the failure. Any threads on this topic would be nice. I also want to say thanks to all the members of this forum. I used to come here a couple of years ago, but have slipped away. Keep up the good topics and discussion..
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Old 09-06-2004, 11:46 AM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Check the blower fuse, little box in front of the fuse box. A strip fuse just like the GP fuse, tends to crack in the center from flexing and leaves you with no blower.

Bad CC fuse will roast you out of the car on the road, so that's not it.

May have a bad cabin temp sensor blower, it's underneath the right side dash vent, have to remove the glove box to get to it. Hose can fall off, motor can go bad, so no air flow past the senor (which is in the dome light assembly, behind the little grille). Test by seeing if a 1 cm square piece of tissue paper will stay up there with the engine on and CC on. If not, either the blower or the Pushbutton unit is dead.

Pushbutton unit is unique to the diesel, I think (may be the same as teh 300SDL unit), so be carefull if junkyard shopping.

You may want to pull it and spray contact cleaner onto the temp wheel rheostat, mine was dirty in the TE and caused continuous mode switching.

You may also have a defective compressor clutch -- I've seen them with the rubber between friction and hub torn, so the compressor won't drive even though everything else is fine. PITA to remove, though.


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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Old 09-06-2004, 12:06 PM
jobah's Avatar
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Join Date: Jul 2001
Location: Chicago native-W.MI transplant
Posts: 281
my ACC behaved like yours and it turned out to be some desoldering of the two pots that are associated with the spin wheel. I would get random results (i.e., contact would be made then lost, then made, then lost....).

THis was 12 years ago, and still going strong with the original ACC.

'84 (11/83) 190D 2.2 5-Speed; Silver/Blue; Motor No. 00354, 402k mi (340+kmi mine)

'89 Porsche 911 Turbo Coupe; Black/Black; 53kmi
'05 BMW 530i 6-Speed; 302kmi
'19 Range Rover; 30kmi
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Old 09-06-2004, 03:37 PM
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Thanks Again, I'll check the items that you listed and let you know..

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