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  #1  
Old 11-26-2011, 10:21 AM
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Lost heat in 300d

Hi all,

Cruising down the highway two nights ago, suddenly the heat stopped working in my 300d. It just started blowing cold air. Interestingly, before it stopped, when the heat did work, it only blew out of one of the air vents. When it stopped and only blew cold air, it blew it hard out of all the air vents.

I've been reading here about the monovalve. Where is it and is that the problem? Any other ideas are greatly appreciated. It's getting cold.

Many thanks,
BS
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  #2  
Old 11-26-2011, 10:36 AM
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On the firewall right hand side near the battery. Try unplugging it.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #3  
Old 11-26-2011, 10:41 AM
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Thanks, Kerry. I'll give it a try.
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  #4  
Old 11-26-2011, 10:48 AM
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Guess I'm just not seeing it. Is it under the battery, perhaps?
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  #5  
Old 11-26-2011, 11:01 AM
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Quote:
Originally Posted by sides View Post
Hi all,

Cruising down the highway two nights ago, suddenly the heat stopped working in my 300d. It just started blowing cold air. Interestingly, before it stopped, when the heat did work, it only blew out of one of the air vents. When it stopped and only blew cold air, it blew it hard out of all the air vents.

I've been reading here about the monovalve. Where is it and is that the problem? Any other ideas are greatly appreciated. It's getting cold.

Many thanks,
BS
What year 300D is it?

From what you describe occurring with the air vents, it sounds more like you have a problem with the acutuators for the vent flappers (ie, vacuum problem), and/or a problem with the CCU itself.

A problem with the CCU itself would explain both symptoms - if the CCU went funky and decided to shift from heat to vent mode, that would explain the change in air flow from the vents, and commanding the monovalve shut would explain the sudden lack of heat.

The monovalve by itself going south wouldn't explain the change in air flow out of the vents.

A loss of vacuum to one or more of the vent flap actuators, depending on which ones, could explain both symptoms as well, but after experience with my two 87 300D's, I'm sort of doubtful of that.

I'd first do a vacuum test on the vent flap actuators, to eliminate that possibility. If they check out, check the monovalve and aux water pump to ensure they work and eliminate that possibility. If they're OK as well, I'd say you're left with a flaky CCU (for whatever reason) to blame.
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'87 300D 212K miles
'87 300D 151K miles - R.I.P. 12/08
'05 Jeep Liberty CRD 67K miles
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  #6  
Old 11-26-2011, 11:08 AM
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Thanks, Mitchell. I'll dig in deeper and look at the CCU itself.

On a working version of one of these CCU's, how do you activate vent mode, anyway? I never could figure out how to simply get fresh air flowing through the system. Very confusing.

Also, where exactly is this monovalve? Kerry said on the firewall, right hand side near the battery, but all I see are hoses.

Thanks,
BS
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  #7  
Old 11-26-2011, 11:12 AM
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Monovalve pic

Quote:
Originally Posted by sides View Post
Hi all,

Cruising down the highway two nights ago, suddenly the heat stopped working in my 300d. It just started blowing cold air. Interestingly, before it stopped, when the heat did work, it only blew out of one of the air vents. When it stopped and only blew cold air, it blew it hard out of all the air vents.

I've been reading here about the monovalve. Where is it and is that the problem? Any other ideas are greatly appreciated. It's getting cold.

Many thanks,
BS
Try this link. Very good reading
whunter has provided pics of the monovalve in post #20

Damaged mono valve pictures please
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  #8  
Old 11-26-2011, 11:44 AM
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Thanks for the pics. But I still can't find the monovalve housing on my car!
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  #9  
Old 11-26-2011, 12:15 PM
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Need year and model.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #10  
Old 11-26-2011, 12:37 PM
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Sorry - it's a 1977 300d non-turbo. At least that's what the VIN # and the manuals indicate; the license plate people say it's a 78. Thanks, Kerry. I can't find the monovalve anywhere, but I think it's the CCU.
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  #11  
Old 11-26-2011, 06:44 PM
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77 explains it. You don't have one. You have the evil servo. Search on evil servo or servo for lots of info.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #12  
Old 11-26-2011, 06:52 PM
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If you need immediate heat without spending a lot of money for a new servo, search on servo bypass.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #13  
Old 11-26-2011, 06:54 PM
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It's far less likely to be the CCU with your system and far more likely to be the servo. The servo is far more dependent on vacuum and has a central vacuum control switch, which , if it fails, won't let the system operate. If you search on my user name and 'servo manual' I posted a link to anonline manual fo rthe servo system.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #14  
Old 11-26-2011, 08:42 PM
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Answer

Quote:
Originally Posted by sides View Post
Sorry - it's a 1977 300d non-turbo. At least that's what the VIN # and the manuals indicate; the license plate people say it's a 78. Thanks, Kerry. I can't find the monovalve anywhere, but I think it's the CCU.
This may help you.


Evil Servo service manual
Evil Servo, service manual - PeachParts Mercedes ShopForum

Evil Servo bypass
Evil Servo bypass

Maybe pictures will help. Trying to get my heater working. Where to start?
Maybe pictures will help. Trying to get my heater working. Where to start?


ACC servo unit = Heater Control Servo



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1973 300D
1973 309D - stolen
1978 280SE
1980 240D
1983 300D
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  #15  
Old 11-27-2011, 01:30 PM
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Thanks so much, folks. Seems a complex and thorny subject.

I'm gonna bypass. Does anyone have pictures of a completed bypass?
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