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  #1  
Old 09-06-2011, 07:22 PM
85 300TD
 
Join Date: Sep 2011
Location: Charleston SC
Posts: 45
First Thread! 2 AC problemas..

Hey Everyone!
Been reading a lot on the forum and there is some great info! I have tried the search function and can't quite find the answers I am looking for.

Anyway, we are proud new owners of an '85 300TD. Been redoing quite a few things including brakes all the way around, center driveshaft bearing, and of course lots-o-vacuum problems.

Just dropped about $900 on the AC system and it's finally working (kind of). The first problem is when the air is blowing, so is the heat. I can clamp off one of the heater core lines and the system cools down nicely. I am guessing it's in the control box under the dash (where the center vents are malfunctioning), but I am not sure. Is this where I should be looking?

2nd problem is obviously the classic center vent issue. I have the glove box out and was wondering if it's possible to take the top half of the dash off (dash pad) or do you have to remove the whole dash? I plan on removing the push rod pin from the actuator to fix this issue.

Oh! What is the correct way to disconnect the vents? The shop disconnected the passenger and broke it, so now it's glued together and I can't get it back in snug.

Any help would be greatly appreciated!!

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  #2  
Old 09-06-2011, 07:30 PM
Registered User
 
Join Date: Jan 2002
Posts: 18,350
Try replacing the monovalve.
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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 09-06-2011, 09:10 PM
Registered User
 
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
Monovalve repair takes about 5 min. This is the kit you will need: http://catalog.peachparts.com/ShopByVehicle.epc?q=1985-Mercedes--Benz-300td-Climate--Control&yearid=1985%40%401985&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6234%3AED%7C10000135%3AMBC%7C1518%40%40300TD&catid=242213%40%40Climate+Control&subcatid=242328@@Mono+Valve+Repair+Kit&mode=PD
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Sam

84 300SD 350K+ miles ( Blue Belle )
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  #4  
Old 09-06-2011, 09:15 PM
vstech's Avatar
DD MOD, HVAC,MCP,Mac,GMAC
 
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,835
First thing I'd do is measure the voltage to the connector on the monovalve. if it's got 12V AT the connector, then the CCU is working properly, and the problem is definitely in the monovalve. it could be seized in the open position, or the diaphram could be torn.
if there is no voltage at the connector, you must have positive and negative at the connector. don't measure positive at the connector and ground the lead to the motor... the ccu modulates ground to control the flow of heat.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
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  #5  
Old 09-07-2011, 07:49 PM
85 300TD
 
Join Date: Sep 2011
Location: Charleston SC
Posts: 45
Thank ya'll very much!
I will check voltage to the monovalve and go from there.

Cheers!
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  #6  
Old 09-10-2011, 02:12 PM
85 300TD
 
Join Date: Sep 2011
Location: Charleston SC
Posts: 45
Monovalve definitely bad. I will see if I can scrap one off of another TD I know of.

Thanks for the help!

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