Help.One of my mercedes is a 1980 450sl with only 50k miles on it.I seldom drive it today I took it for a drive,and noticed the climate control was not working.the fail safe defrost would give me pleanty of heat and blower.But no other button would react at any temp setting.The last time I used the car the climate control worked.Help.Michael.

The 1980 450SEL and SL have similiar circuitry and failsafe mode (which you've discovered one of them).

For the 450 SL, check fuse numbers 6 (16 amp) and a inline fuses. The inline fuses are in the fuse box. They look just like the type you see on car radios. one is 2 amps and the other is 8 amps.

Anytime any of those go, it's all or nothing heat. Not bad for a limp home mode, 'cause it could be worse.

PLEASE let us all know if that's the answer.

__________________
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)

J.R.Thanks for helping.All of the fuses appear to be ok.I will put a meter on them to be sure.The inline fuse you mention I cannott find.In the box all of the fuses are the same type.with diff ratings of corse.Again thanks.When I get it working I will let everyone know what it was.Michael.

Michael,

Pull the main fuses involved and check with an ohm meter.

Regarding the inline fuses. There is an auxillary fuse box on top of the main fuse box. Unless there is an error in my MB Electrical Troubleshooting manual, that's where you'll find them.

Good luck from California, MD (just South of Hollywood ,MD)

__________________
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)

JR I will give that a shot.You and I are almost neighbors.My daughter live near hollywood on the water.I live on the family farm.If I find you in the book I will give you a call Best Regards Michael.

JR.In the sl the fuse box is in the pass.side kick panel.If there are any fuses anywhere else.I cannott find them.They do not show up in the owners manuel.Could the thermo switch at the bottom of the servo be causing this.I will repeat symptons.Plenty of hot air in defrost.No other button responds except to change the vacume flap settings.When I turn the car off I can hear the servo run to its park position.Could I hire you to solve this problem.I do not live very far away.Best regards Michael.

You have a vacuum problem. With no vacuum on the master switch nothing works EXCEPT defrost which is always HOT.

To test, verify the vacuum on the temp switch at the base of the servo unit (in the engine compartment). Both sides of the switch should have vacuum. It goes from there to the pushbuttons and the master switch.
.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Michael, No you can't hire me to fix it, but I'd be happy to help a Fellow Benzer look under the "hood" and investigate Steve's suggestion (which is code for "more than likely").

Drop me an email.

__________________
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)

A common problem in the cars with the servo(black unit on the right firewall) is cracking at the base which lets antifreeze get into the motor.Have someone turn the key on and listen to the servo. You should hear it running a cycle. If not look at the base and see if there is any sign of cracking or leaking.If you see a crack replace it!

I can hear the servo go to park when I shut the car off.JR I found those other fuses,I had to take the pass side under dash panel to find them.Still no luck finding problem.I have vac at the yellow line going to the temp switch at the bottom of the servo.I tried bypassing the temp switch by hooking the yellow and black together.no diffrence.All of the vac flaps seem to be operating but I cannott get the fan to blow anywhere but defrost.

Do you have vacuum in both lines when the blower isn't working. You need to tee into the line. If you have vacuum on both sides then you need to find the blower vac switch and see if vacuum is getting to it.

Bypassing the electrical portion of the swicth will undoubtably give back your blower functions. Try it as a test. Unfortunately you can't just leave it bypassed as you will find that the system can not be turned off in that case. You will need a vacuum schematic to find the leak.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,

Regarding the vacuum in both lines. If I understand your post, your saying regardless of coolant temp, pull both line (black and yellow) at the Temperature switch (in effect bypassing the 40C opening), place a T between the lines, install a vac gauge and test (engine operating). I also suspect that if one doesn't hear the typical vacuum leak down when a system is pulled apart then there is more than likely a leak. Then the search is from there (backwards and forwards for the vacuum leak.

About how many bar/inches of Hg would you expect to see with a properly functioning system? The same as measured at the engine vacuum connection?

Also, Is there enough similarity between the 116 and 107 ACC that a 116 ACC MB Service manual (specifically the vacuum diagrams) would work?

__________________
S, J.R. Brown
2000 G500 LWB Obsedian Black
2005 Toyota Tacoma Access Cab Off Road Sport
1993 Volvo 240 Sedan Anthracite
1980 450SEL Champange (owned it for 15 years. Great car)
1986 280GE LWB Anthracite (Sold it and kinda wish I hadn't)

No... You misunderstand what I am asking. I will attach a picture of the gauge arrangement I suggest. The picture was done for an article I wrote that will appear in next months "Import Car" on diesel transmission adjustments. The hose is the white MB hard plastic vac line and I am using a 4 way but a 3-way is what is easiest. (vac line 000 158 14 35, 3-way 117 078 01 45 the line is sold by the meter and is a little over a dollar a meter)

What I am asking is that you insert the gauge into the system (AS IT IS DESIGNED - non-intrusive testing so to speak). I am basically wanting to see if vacuum is in either line as this is the easiest place to test (that I could describe in writing). The switch is usually open (especially in Florida), testing on both sides confirms it. If vacuum is here then you usually will have it at the master switch, which is much less convenient to test. The point to all this is your main symptom: only defrost works. This almost has to indicate a problem in the master switch as it is hard to imagine any other blower problem that could cause that symptom.

The switch and all elements will work at very low vacuum levels maybe as low as 3in vac. The system also has a programmed leak so it won't maintain vacuum without the engine running. This programmed leak will throw you. It is a bundle of green wire plugged into a tee. Evidently the vacuum makes it out through the strands of copper.

The system in the SEL is basically the same. There is one different switchover valve and some different vac elements as the dashes are different but the designed and control concepts work in either the same.

Attached Thumbnails

 

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks for all of the help.I will give the latest a try.JR.did you get the e mail I sent to your home.Regards Michael.

its alive its alive.I did everything yall said nothing worked.I wiggled wires and hoses,all of the sudden it started working as good as new.I dont have a clue as to what happened.The next time I try it I may be back to square one.Will keep you posted.thanks everyone.