Mercedes-Benz Forum banner

1 - 15 of 15 Posts

·
Registered
1983 300D
Joined
·
9 Posts
Discussion Starter #1
My problem is the CC stays on defrost. It works on all setting but only blows out the defrost vents. The temp control only works on max hot or cold, no in-between. After search this site and Google I have concluded the the CCU needs to be replaced or re-soldered. Do you guys think this is correct? Is there something else I need to look for? I am not familiar with these cars at all.

Oh Yea I'm working on a '83 300D.
 

·
Registered
2013 MINI Copper S Clubman, '84 300CD-weekend car
Joined
·
10,152 Posts
I think you're on the right track, pull the unit and inspect.
 

·
Registered
1985 Euro 300TD Turbo, 1983 Euro 300TD turbo, 1979 Euro 240TD and 1981 300D converted to euro.
Joined
·
2,700 Posts
and temp senor in the center to of the dash.
 

·
Premium Member
W-1-2-3 Go!
Joined
·
16,161 Posts
If the CCU is either blowing all cold or all hot air then it could also be a sensor issue. Check the sensor if it's sensing cabin temp. If it is check the foam hose behind the dashboard/glovebox, if this hose is deteriorated it will not allow the cabin sensor to provide feedback to the CCU, so the CCU defaults to full heat or full cold all the time. The foam hose is a 1/2" inner diameter hose if you want to replace it with aftermarket (Home Depot) - the dealer may have a replacement for you as well.
 

·
Registered
1985 Euro 300TD Turbo, 1983 Euro 300TD turbo, 1979 Euro 240TD and 1981 300D converted to euro.
Joined
·
2,700 Posts
If the CCU is either blowing all cold or all hot air then it could also be a sensor issue. Check the sensor if it's sensing cabin temp. If it is check the foam hose behind the dashboard/glovebox, if this hose is deteriorated it will not allow the cabin sensor to provide feedback to the CCU, so the CCU defaults to full heat or full cold all the time. The foam hose is a 1/2" inner diameter hose if you want to replace it with aftermarket (Home Depot) - the dealer may have a replacement for you as well.
senor at the dealer is around 50 bux shop cost.
 

·
Registered
1983 300D
Joined
·
9 Posts
Discussion Starter #7
Thanks for the help. I went through the CCU last night and checked it this morning. When switching through the functions I could get it to change off of defrost but wouldn't blow out anywhere. By the time I got to work it was on defrost again and wouldn't change again. I'm going to pull it and check it again and check the sensor while I'm at it. I'm assuming the sensor is the one in the center of the dash on top.
 

·
Registered
1984 300D
Joined
·
492 Posts
In addition to the foam hose that falls apart, I replaced the rubber diaphragms in all the vacuum actuators. Two of them were ripped, and three more tore apart when I pulled on them. The vacuum actuators are what opens and closes the flaps to direct the air through the various vents. Vacuum is turned on and off to the actuators by the vacuum solenoid valves (VSVs) that are behind the climate control (CC) unit. Those VSVs are what your CC unit operates. Once I got all this fixed, my climate control works like magic.
 

·
Registered
1983 300D
Joined
·
9 Posts
Discussion Starter #10
Thanks for the input everyone. I haven't had a chance to pull the ccu again and check all the things you mentioned. Hopefully this weekend. I'll keep you posted.
 

·
Registered
1983 300D
Joined
·
9 Posts
Discussion Starter #11
Okay, I was able to go through everything on the CCU. Everything seems to be functioning properly which leads me to belive that it is vacuum related now. Does any one know which line provides vacuum to the CC? I want to put my own vaccum source on it before I start tearing into the vacuum actuators.

Thanks again for the help.
 

·
Registered
1983 300D
Joined
·
1,248 Posts
Okay, I was able to go through everything on the CCU. Everything seems to be functioning properly which leads me to belive that it is vacuum related now. Does any one know which line provides vacuum to the CC? I want to put my own vaccum source on it before I start tearing into the vacuum actuators.

Thanks again for the help.
Pull the driver's side underdash panel and there is an actuator near the throttle pedal. If you can use your hands and push the actuator closed, you can get air going through the vent. Then you can pull the line from the actuator to see if it is holding vacuum.

If it is not, then a replacement actuator is necessary or a rebuild kit with new diaphragms are much cheaper route from:
"Performance Analysis Co." owner George Murphy
969 Oak Ridge Turnpike, Suite 258. Oak Ridge, TN 37830
865-482-9175


.
 

·
Registered
1983 300D
Joined
·
9 Posts
Discussion Starter #14
Pull the driver's side underdash panel and there is an actuator near the throttle pedal. If you can use your hands and push the actuator closed, you can get air going through the vent. Then you can pull the line from the actuator to see if it is holding vacuum.

If it is not, then a replacement actuator is necessary or a rebuild kit with new diaphragms are much cheaper route from:
"Performance Analysis Co." owner George Murphy
969 Oak Ridge Turnpike, Suite 258. Oak Ridge, TN 37830
865-482-9175


.

Thanks for the info. I haven't had time to work on it with the holidays. I will keep you posted with what I find.
 
1 - 15 of 15 Posts
Top