Greetings all!
I just bought my 1st MB, a 1987 190E. I got a good deal because it has some "issues"such as the heater is always on full. Not a problem now here in Wisconsin, but may get uncomfortable come July and August. Any suggestions where to start with troubleshooting it??

Thanks

When you say the heat is always on full, do you mean the fan is on high AND the temperature is full-hot?

Jeff Pierce

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Jeff Pierce

Current Vehicles:
'92 Mercedes 190E/2.3 (247K miles/my daily driver)
'93 Volvo 940 Turbo Wagon (263K miles/a family truckster with spunk)
'99 Kawasaki Concours
Gravely 8120
Previous Vehicles:
'85 Jeep CJ-7 w/ Fisher plow (226K miles)'93 Volvo 940 Turbo Wagon
'53 Willys-Overland Pickup
'85 Honda 750F Interceptor
'93 Nissan Quest
'89 Toyota Camry Wagon
'89 Dodge Raider
'81 Honda CB 750F Super Sport
'88 Toyota Celica
'95 Toyota Tacoma
'74 Honda CB 550F

The temp is always on full but the fan can be adjusted with the selector switch.
Don't know if this is related or not. I've noticed that, sometimes, when you accelerate there's this sound of rushing air from the dash (defroster?) like the fan kicks into a higher speed. But I've not noticed any increase in airfllow out of the outlets.

Thanks for the help

Hi - and welcome.

Congratulations on your purchase.

I am no expert but methinks you have lost 12 volt supply to the duovalves -- they fail to the hot setting.

A search in this forum on duovalve/heat/electrical should yield an answer for you.

Happy New Year

NormanB

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NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K

Either loss of vacuum to the heater control valve or the valve diaphram itself. The valve is under the cowl behind the battery area. You might have enough leaking servos inside the car to cause enough of a leak for the valve not to close. First off test the valve itself, then start it and check the supply to it. (odds are the valve is bad)



Joe

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Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

1stbenz,
I had the same symptoms on my wife's '91 190e. I just fixed it a month ago.

Test the heatermonovalve first then start testing the vacuum elements under the dash. In my case, the monovalve was good but I had two bad vacuum elements under the dash: the defroster element and freshair/recirc. element.

I took the dash off and replaced the two elements and also the heater potentiometer while I was there(they frequently go bad).

Everything works now. Let me know if you have any ?'s. I wish I had taken pics while I did it...

What are you refering to by "heater pot" ? I noticed in the Haynes manual they show 2 knobs for the heater control. Mine has 1 temp select knob and pushbuttons for the defrost/heater etc functions. There are 2 pots on the circuit board that that this knob controls. Is one of these the pot your refering to?

Thanks every one for your advice. I'll start checking it out this weekend and let you know what I find.