190/16 Valve A/C and Engine Idle Stability Is Intermittent

[JimSmith]

Hi, I hope someone can help me out here. My 1986 190E 2.3-16, a grey market vehicle I imported new in 1986 and have used as daily transportation for the last 15 years now has 199,450 miles and still runs strong. I recently started using a lot less oil, and get around 2 to 3 miles per gallon better mileage, so I think it is really breaking in, finally. When I got it new it used about a quart of oil every 1,500 to 2,000 miles and got 23 to 24 mpg. Today it uses no oil between oil changes (3,000 to 3,500 miles, always synthetic, either Mobil 1 20W50 or Castrol Synteck 5W50) and gets up to 27 miles per gallon. So the machine is in relatively good shape.

Around 110,000 miles ago the idle control died, and the car would stall all the time. I had the "idle-motor" on the intake manifold replaced and the problem went away. The new one was significantly different in shape than the original part, but it fit and works great. Until last summer, when the car began to idle at a high rpm most of the time. Some times the the idle would be normal (900-1100 rpm) but for the most part it would be around 1500 to 1800 rpm, regardless of the engine temperature. This had no significant effect on the mileage.

Then, also last summer the A/C would decide on its own when it would be on. The factory A/C in this car is the manually controlled variety as the fancy climate control system was another $2400 and for that kind of cash in 1986 I felt turning the A/C on and pushing a little lever to control how cold it got was a better deal. The intermittent A/C operation is becoming more off and less time on these days, and I cannot figure out where the problem is. When the A/C is on, it provides good cold air, so I do not think the freon charge is the issue.

I have been reading threads mentioning the overvoltage protection relay for this car having some control over the idle and the A/C operation. At present the idle seems ok, but the A/C is still acting up. Any clues?

I also noted the auxiliary fan hardly runs, if ever. It is not siezed, but I have not heard it lately and when I run the car hard in hot weather, or get stuck in traffic idling, the car heats up pretty good. There is a resistor mounted on the driver side inner fender that has some corrosion on the connections, which I will clean off today, but is there a resistance value for this item I can check?

Thanks for any ideas. Jim

The idle problem could be either the overload protection relay or once again the idle air valve. If it is OK now, then let it be.

The AC could be a problem with the AC Comp. relay (KLIMA), or any of the inputs that tie into it.

The ballast resistor for the aux. fan is there to step down the fan speed when the red (or green on early cars) switch on the drier turns the fan on. Just check the resistor for continuity. When they go bad they go 'open'. If you jump the red switch on the drier with the key on, then the fan should turn on.

[JimSmith]

Thanks, I will try by-passing the switch on the drier tomorrow afternoon and let you know. I found the "KLIMA" relay this afternoon and pulled it out to check the pins for corrosion and general condition. There was a little green stuff on it, so I cleaned it off and cleaned the receptacle with a spray cleaner and a little wire brush. No net effect. I there a way to check the function of the relay with a multi-meter? Thanks.

[crookednose]

Where is the Klima relay located and what does it look like? I want to check this on my 1987 190 Euro.

[JimSmith]

The "KLIMA" relay is located directly behind the battery. In my car there is a thin black piece of plastic right behind the battery that is held in place by the formed rubber gasket that seals between the hood and the engine compartment at the firewall. If you raise the hood to the 90 degree position, this rubber gasket lifts off the firewall, and then the plastic shield also lifts out. The "KLIMA" relay is about an inch thick, and two inches wide and two or three inches tall. It is a black plastic box, and has the words "KLIMA 4 ZYL. 12 V" in fairly large white letters on the top. It sits behind a relay, same basic size and shape, that says "4 ZYL 7100 min KVS" on the top.

I took out both of the relays and cleaned them and then put them back in. The pull out vertically and have the ususal Mercedes-Benz array of silver plated eighth inch diameter pins on the bottom. They were a little hard to pull out, mainly because there is not much room to get a good grip on them in the little cubby hole they sit in.

Good Luck. Jim

[JimSmith]

Well, I have checked the reistor and shorted the drier switch with no changes. Is there a relay that controls the auxiliary fan anywhere? What about the A/C compressor clutch? Is there a way to check that circuit? Thanks, Jim