Two Problems: A/C & Oil Light - PeachParts Mercedes-Benz Forum

Tump · #1 06-04-2002, 07:09 PM

Hello All!

First off, I love this web site, have learned a lot and have basically restored my '87 300E completely.
There are, however, two remaining annoying problems that I'd like to fix by myself or with the inexpensive help of my MB mechanic (if the repair time is under 2 hours at $85/hr).

After doing all possible high mileage repairs at about 180K, ie: the head (gasket(s), valve guides, seats and all), the radiator, all hoses, water pump, mono belt, tensioner pully, alternator, a/c compressor, blower motor, shocks, brakes, wheels and tires -- I love the car and it drives like a dream! I removed the resistor that retards the timing 6 degrees BTDC and the car gained 11 hp, operates at a lower temp., and gets about 20 mpg, driving hard. With a perfect obsidian black exterior, a palomino interior and an Alpine/Competition MB Quart CD changing system, I want to keep the car going as long as possible. It will never be financially reasonable to sell it, so ...

Problem 1:
The engine is very tight now and doesn't burn or use any oil, and I've been running Mobil1 Tri Synthetic 0W30 (winter) and 5W30 (summer). These lubricants seem to work very well to quiet the engine substansially at high rpm's and to lower it's operating temperature (80-81 c. at all outside temp's w/ A/C on or off). However, the oil level light on my instrument panel lights up often when going up or down a hill, under heavy braking and under hard acceleration. The light comes on for a second or two and then goes off. This happens even though the oil is at the correct level (I check it often manually) and whether I use the O or the 5 weight oil. My mechanic suggested that I replace the oil level sender unit with a new one, he did, and the problem remains the same. Any ideas or suggestions? Is the viscosity of my oil too low to properly trigger the oil level sender switch?

Problem 2:
Eventhough I have a new A/C system w/ 134A, a Nippondenso condensor, and a new MB suction hose, that blows very cold air -- the system still has a problem. When I set the fan to high and the blower motor makes a lot more noise and seemingly blows a lot more air, not much air comes out of the center or side vents (during A/C or heat operation). In a fully functional system, the air should blow your hair back with the fan set on high. With my system, you can barely feel the air on your cheeks when the fan is set on high.
The pushbutton control unit works, it is new I just replaced it, I replaced the mono valve and I disconected the aux. water pump (I will replace it with a new one at the begining of the winter). My mechanic thinks that the flap behind the center vent is stuck or that its operating diaphram is ruptured or that there is a vacum leak somewhere. Does this seem right? If so, how expensive is this to fix (how many hours) and could a reasonbly handy guy (me) do the work himself? Are any special tools needed? Any opinions or help would be appreciated.

I have another subject that I will make the subject of a seperate post.
Marc
Restored87300E

euro 287 · #2 06-04-2002, 08:44 PM

First thing you would have to do on the a/c actuator problem is figure out which one is leaking, on the passengers side that carpet panel that runs along side of console , remove the one screw from it and pull the panel gently toward the front of the car ( it tabs into the console) after you remove that take a mityvac tester and ck all the vacuum lines on the switchover valve block. Tell us the color of the ones that leak. The switchover valve is mounted on the case.

bluerhino · #3 06-16-2002, 10:59 AM

Hi Tump,

What's the status on your problem #2? I have the same problem at the moment - less cool when the a/c is on high and relatively ok when the setting is minimum.

Thanks.

Tump · #4 06-17-2002, 10:46 PM

Hi Bluerihno:

I followed Euro 287's advice and had all the vacum lines checked. The lines that control all the valves/air flaps with vacum switches and the "vacum pot" behind the instrument panel. The diagnostic was not expensive: 1 hour of labor. The good news was that all my vacum lines were fine and that, there were no leaks. The bad news, however, was that the mechanic concluded that, because the vacum switches were working, the blower motor had just been replace and the air flow was still so reduced that, the vent flap comming out of the heater core must be either stuck or broken or jammed (somehow permanently fixed at 1/3 open). Fixing this inexpensive valve would be very expensive. It involves, my mechanic explained, about 13 to 14 hours of labor to remove the dashboard and locate the valve at the base of the heater core and replace it. It's so expensive to fix that I decided to live with the reduced air flow problem and keep my air on "low."

Then, as luck would have it, I decided to take the Benz dealer up on his offer to let me trade in my old 87 300E for $9K against a 1999 C43 AMG (w/ 40,000 miles)(Black on Black) just brought in off lease. I'm very excited, and should get the newer car this Friday.

Marc
99C43 AMG

bluerhino · #5 06-17-2002, 11:39 PM

You're solution is absolutely perfect. Should I ran out of patience, I think I might do that myself.

To be honest, MB is beginning to be a challenge to me. It is troublesome as compared to my other car but for some reasons, we're all hanging on.

Amuso · #6 06-18-2002, 10:52 AM

I'm interested in finding out where the resistor that controls the BTDC is located, and how to remove it for gained hp.

Tump · #7 06-18-2002, 04:57 PM

Dear Amuso:

On the 87 300E and 86 300E, I believe, that resistor is located just in front of the fuse box on the driver's side of the engine bay, behind the firewall. It is held onto the low pressure ac line (the one with a blue cap) with a wire tie. Slide the wire and resistor out from under the wire tie; remove the plastic male connector that holds the resistor; cover the remaining female plastic connector on the end of the wire with electrical tape; slide it back under the wire tie on the low pressure ac line. Total time: 3 minutes. Alleged horsepower gain: 11. Do a search on "resistor" to read the posts on the subject.
Marc
C43 AMG