87 300SDL --- weird, erractic AC issues - PeachParts Mercedes-Benz Forum

ah-kay · #1 05-02-2012, 11:29 AM

Quote:

Originally Posted by daw_two

So, I attempted to build a simple ice cube relay to control the AC compressor with just the ACC thermostat wheel. After that failed (I guess there's a reason why I'm not an Electrical Engineer), I kept staring at the KLIMA relay that I have from that 1991 350SD parts car. I turned it over and saw the labels on the pins --- they are the same as the 300SDL. Plugged it in and cycled the key and ACC unit and presto, I have working AC.

I did test to see if jumping "hole" 5 & 7 and sure enough that powers up the compressor without any protection.

Oh.....btw....after I turned the car off, I remeasured the resistance between "hole" 9 & 11 (speed sensor) and measured 707 ohms. I'm guessing the range of 530 to 650 ohms is a cold measurement.

So, it looks like my existing KLIMA relay was the culprit.

Anyone want to give me a lesson in reading/interpreting the KLIMA relay diagram?

Good job. I do not realize that you have a 19i91 SD parts car. The Kilma should be compatible. So the time I spent last night to hack the Kilma circuit and PM'ed you was all in vain.

The problem is the Kilma, not the speed sensor in the compressor. Speed sensor rarely goes wrong unless it is open circuit. The speed sensor measurement is done by a IC differential circuit. One cannot fix it unless one knows the part number.

daw_two · #2 05-02-2012, 11:38 AM

Quote:

Originally Posted by ah-kay

Good job. I do not realize that you have a 19i91 SD parts car. The Kilma should be compatible. So the time I spent last night to hack the Kilma circuit and PM'ed you was all in vain?

Nope --- I'm thinking of modifying my old KLIMA to be used as a standby.....in case I have this issue in the future. Thanks for the drawing --- saw it this morning --- I'm still trying to understand how that thing works and how you can get by with tying those 2 together.

I tried 3 times to pass Circuits I in college. After my third time dropping the class, I decided to change my major from Electrical Engineering.

daw_two · #3 05-03-2012, 11:04 AM

Well......maybe it wasn't the KLIMA. Why is it so hard for me to spell that word correctly? I have spelled it KILMA many more times.

Anyway, so, yesterday, I had one AC hiccup where the air started blowing warm. Cycled the key off and then restart the car and it was good the rest of the day. Here's my next hypothesis:

Full Throttle Microswitch

So, I know where it is located. Is it serviceable? Does it "stick"? Can it be cleaned? The one AC hiccup yesterday seemed to have occurred right after I started from a dead stop (red light) and I was in a hurry to get to my 2pm appointment. Maybe, I did "get" the throttle all the way open --- it's hard to tell from a dead stop in a 300SDL.

brandlj · #4 05-04-2012, 09:06 AM

It will take 2 people to check this, but perhaps your accelerator linkage is not adjusted correctly. Perhaps the linkage is closing the microswitch in the engine compartment before you are at wide open throttle. Shine a light on the switch while someone steps on the accelerator and make note that the microswitch should not be closed unless the pedal is all the way to the floor.
If the throttle linkage is adjusted correctly, perhaps the switch is sticking. I would think a spray of electrical contact cleaner should help.
Good Luck. It is too hot already to start having A/C problems!

daw_two · #5 05-04-2012, 11:05 AM

Quote:

Originally Posted by brandlj

It will take 2 people to check this, but perhaps your accelerator linkage is not adjusted correctly. Perhaps the linkage is closing the microswitch in the engine compartment before you are at wide open throttle. Shine a light on the switch while someone steps on the accelerator and make note that the microswitch should not be closed unless the pedal is all the way to the floor.
If the throttle linkage is adjusted correctly, perhaps the switch is sticking. I would think a spray of electrical contact cleaner should help.
Good Luck. It is too hot already to start having A/C problems!

Thanks, John !!! Yes, I know it's already too hot here for AC problems.

Yesterday, I was waiting in the parent car line for Middle School to let out at 2pm. All of a sudden, I notice the AC was starting to get warm, looked down at the temperature gauge and it had crept up to that mark between 80 and 120 (is that gauge linear? Would that be 100C?).

I definitely need the aux fan to come on sooner. I wonder if I have a "lower" temperature aux fan switch somewhere. Here are the different configurations and what some other forum members have done in the past:

603 Aux Fan Switch (mounts on the dryer, correct?)
Red: 006-545-42-24 (100/110)
Green: 006-545-45-24 (105/115)
Grey: 006-545-61-24 (105/120)
Blue: 006-545-64-24 (105/128)

The first number in parenthesis is the temperature that the aux fan engages at high speed, and the second number is when the AC compresor will cut out.

HitMan_X installed the red one
gsxr installed the grey one

Oh, WAIT a minute. Is the temperature/aux fan switch (green in my 87 Champagne) in direct contact with the R134A ??

Hmmmmm......

brandlj · #6 05-04-2012, 04:39 PM

My 86 sdl originally had the green switch. When I just rebuilt the A/C system, I installed the red switch. I do believe that it is in direct contact with the R134A.

Years ago I had a 1989 BMW 535i. It was notorious for not cooling very well at idle in traffic with R134A. I actually ran a jumper wire to the two leads of the High Temp fan switch and ran it inside the car to a toggle switch. At idle in traffic I would manually turn on the toggle switch to turn my electric cooling fan on high. It helped a little bit.

ah-kay · #7 05-04-2012, 04:52 PM

Quote:

Originally Posted by brandlj

My 86 sdl originally had the green switch. When I just rebuilt the A/C system, I installed the red switch. I do believe that it is in direct contact with the R134A.

What do you mean by direct contact?? The p/n switch is the thermostatic switch on top of the cylinder head. It will NOT be in contact with any R134A or R12, they are poles apart.

The slow speed of Aux fan is controlled by the high pressure switch at the Rec/Drier.

The high speed of the Aux fan is controlled by the thermostatic switch on top of the cylinder head when the coolant reaches 100, 105 ( depending on color code of the switch ). AC will be cut off when it reaches the 110-128 temp by the Kilma sensing the switch.

A Man · #8 05-07-2012, 12:53 PM

Quote:

Originally Posted by ah-kay

Good job. I do not realize that you have a 1991 SD parts car. The Kilma should be compatible. So the time I spent last night to hack the Kilma circuit and PM'ed you was all in vain.

Perhaps it was not all in vain!

Anyway I can get a copy of this? I am having issues with my A/C as daw_two knows. The patient is a 1991 350SD. (I could use a 350SD parts car too lol) I've charged the system with refrigerant and can now get the clutch to kick in by connecting pins 5 & 7. With the car idling, clutch engaged via jumper, I have a 228mvAC signal on pins 9 & 11 but nothing on pins 1 & 2. Upon disengagement, the voltage goes to about 5mv. Pins 9 & 11 are the compressor speed signal, right? Is this a good operating signal while engaged?

Pins 1 & 2 should be the engine speed, correct? As far as I am able to interpret the schematic, they are the tachometer signal after it comes from the EDS. I have a 4.28VAC signal from the pick-up on the flywheel but no tach on the dash, and nothing on these pins at the KLIMAY relay. Anyone have any ideas what might cause this?

I have replaced the single 10A fuse in the OVP, since the ABS light was on and the idle was rough. The ABS light went away, I can't tell if the idle improved.

I'm about to make an 8 hour weekly work commute to south LA from AR and I would very much like to have the comfort of A/C

PS Daw_two thanks for the info on the fuel thermostat! I was able to bypass it and drive the car home last week.

A Man · #9 05-17-2012, 12:26 PM

Quote:

Originally Posted by A Man

I have replaced the single 10A fuse in the OVP, since the ABS light was on and the idle was rough. The ABS light went away, I can't tell if the idle improved.

Well, I removed my OVP relay from the car to investigate if there was any internal damage. I attempted to remove the metal cover but after stabbing my finger with the pick and nearly stabbing my chest,

I gave up. Lo and behold, when I reinstalled the relay in the car with it running, the car went VVVVRRRROOOOOOMMMMMM!!!!! and sat there purring like a cat.

The belt stopped jerking and the car stopped shuddering. I now have a voltage signal for the tachometer on the test connection under the hood, at the KLIMAY relay and all the way to the tach in the dash, but still no operable tachometer.

Addtionally, the SRS light went out on the dash and the A/C compressor switches on from the Climate Control.

Apparently, the OVP relay is not making good contact into the wiring harness as the A/C stopped working during my last commute and the idle went to pot again but a simple replugging of the OVP relay fixed both.

So does anyone have a good working tachometer that they would like to sell?

Thank you all and have a wonderful day!