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

daw_two · #1 05-01-2012, 12:18 PM

Okay, folks, here are the 2 symptoms:

Symptom #1 described:
About 2-3 weeks ago, I'm driving on a warm day with the AC cold air blowing out the center vents.....and the air starts getting warmer....then hotish. I'm running errands, so I stop the car. Came back to the car in a few minutes, start the car, and viola, I have cold air starting to come back thru the center vents.

I'm thinking this is a possible KLIMA erractic malfunction.

It happen 3 times yesterday. AC ice cold air starts getting warmer....turn off key; restart the car, and I have ice cold air again.

Symptom #2 described:
I was playing with the AC a lot this morning. If the AC is on MAX cold (feel the click in the thermostat wheel on the ACC), the AC is icy cold and blowing thru the proper vents including the center vents. I adjust the thermostat just a bit, with the fan speed on any setting, and the center vent seems to switch.......hardly any air flow thru the center vent.....can hear the roar of air moving....buts it's not coming out of the defrost vents.....I turn the thermostat back to MAX cold, and the air flow returns to the center vent.

Weird, huh?

I replace the Mono Valve on this car (87 Champagne) back when I bought it, so, I'm thinking it's not related to it.

eatont9999 · #2 05-01-2012, 01:16 PM

A similar thing happened to my 300SD yesterday after I topped it off with R134a. At idle the AC was cool, not near as cold as I would like, but noticeably cooler than the outside air. I decided to drive the car around the parking lot for a few minutes to see if the AC would get cooler past idle. Well, it stayed the same until it stopped putting out cool air. Suddenly, I was getting ambient temp air. It wasn't hot like the heater was on but about the same as the outside temp.

I have yet to get cool air from the car again.

ah-kay · #3 05-01-2012, 01:22 PM

Problem for symptom #1 is Kilma relay. It happened to one of my SDL, A/C cut off after a while then return after turning off car. I hacked the relay to only monitor the freon switch and everything is OK. I ran the hacked relay for about 1 year without issues until I found a good one in a JY.

Cannot offer anything on #2. Good luck.

daw_two · #4 05-01-2012, 02:54 PM

Since we all know about the engine speed compared to the compressor speed in the KLIMA....and since the 87 Champagne car had a small power steering leak (over the edge --- replaced the seal/gasket on the lid), I'm thinking I will take a shot at cleaning the speed sensor on the AC compressor and see if that fixes the issue.

In addition, I guess I will increase the priority of the vacuum pump replacement, serpentine belt replacement, and tensioner damper. The dancing tensioner is probably impacting the AC compressor speed:
Bought some 1987 Champagne

Anyone want to chime in here about the KLIMA circuit?

Thanks, BC for this post ---- AC challenge: 300SDL compressor cut- out

I've been doing alot of reading....

eatont9999 · #5 05-01-2012, 05:02 PM

I noticed my compressor clutch is not engaging when I have the AC on. What are the correct low and high side pressures for a MB AC system? What should the ambient pressure with AC off be? How can I bypass the Klima temporarily?

brandlj · #6 05-01-2012, 06:14 PM

Hey David,
Symptom #1: Probably Klima doing it's job correctly if your serpentine belt is slipping which is allowing the speed sensor on the compressor to sense this and shut off compressor. If the belt is moving around a lot because of the tensioner, speed of the compressor may not be the speed of the engine.
BUT also, the kickdown switch could be flaky. Kickdown switch shuts off compressor. Also full throttle microswitch in the engine compartment will shut off compressor. Check those things.

Symtom#2: Probably not a Climate control pushbutton unit failure. Default mode for 87 sdl is all of the air will blow out of the defrost only. BUT turning off the car and turning it back on resets the PB unit until it fails again.
But you say you hear roaring, but no air coming out. I am leaning towards the vacuum tree on the passenger side of the footwell. Perhaps an erroneous signal is closing the vacuum to the center vent pod. Of course it could also be the center vent pod. When mine went bad it closed off the center dash vent, but then all the air blew out the foot and defrost.

What you really need is the Climate control Paper book manual so you can run the step by step diagnostics. I have one and will loan it to you if you would like. Just drop me a line.

Summer is almost here, Memphis summer is NE Louisiana summer. It sucks!!!

daw_two · #7 05-01-2012, 08:14 PM

Yeah, John. I think Summer is here today. I wish I would have had an extra shirt with me today, so I could change after coming back from lunch.

Anyway, yeah, I know about the microswitch, but had to find this picture of it to know where it is located:
http://www.w124performance.com/images/OM603_misc/microswitch.jpg

For now, I just unplugged it.

Hmmmm....studying the KLIMA relay circuitry here:
AC challenge: 300SDL compressor cut- out
and
it looks like I can leave the full throttle microswitch unplugged. EDIT --- I seriously doubt it can be left unplugged if the KLIMA is plugged in the socket.

I measure the resistance of the speed sensor using sockets 9 and 11 ---- ouch.....measured 686 ohms. Looks like my speed sensor is out of range.

daw_two · #8 05-01-2012, 11:11 PM

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?

brandlj · #9 05-02-2012, 07:29 AM

Awesome news! Yeah the speed sensor resistance appears to be to high, but then as things get older...
Anyway, I am glad you had another KLIMA relay. Try and stay cool. We are looking at record highs here for the next 7 days with no prospects of rain.

ah-kay · #10 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 · #11 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 · #12 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 · #13 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 · #14 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 · #15 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.