87 300SDL --- weird, erractic AC issues - Page 2 - PeachParts Mercedes-Benz Forum

ah-kay · #16 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.

brandlj · #17 05-04-2012, 08:52 PM

DUH!!! You are absolutely correct. I confused it with the pressure switch on the drier.

daw_two · #18 05-04-2012, 10:30 PM

Well, maybe I'm confused.

Isn't the "Temperature Switch" on the drier what controls turning on the aux fan when the AC is on and the freon (R134A) gets too warm? Maybe the part numbers I quoted were for the Temperature sensor on the head, but I'm talking about the thing on the drier. Is it called something else?

ah-kay · #19 05-05-2012, 01:22 AM

The switch at the rec/dryer is a pressure switch for the SDL. There are 2 switches in the r/d. One low pressure to indicate freon is present and up to pressure. The other one is high pressure switch ( 15 bar? I cannot remember off hand ) to activate the aux fan at low speed.

daw_two · #20 05-07-2012, 09:28 AM

Quote:

Originally Posted by ah-kay

The switch at the rec/dryer is a pressure switch for the SDL. There are 2 switches in the r/d. One low pressure to indicate freon is present and up to pressure. The other one is high pressure switch ( 15 bar? I cannot remember off hand ) to activate the aux fan at low speed.

So, is the high pressure switch in contact with the R134A ? At what pressure does it come on? I thought the FSM indicated the switch on the drier was a temperature switch.

Thanks for the clarification!

ah-kay · #21 05-07-2012, 12:18 PM

Quote:

Originally Posted by daw_two

So, is the high pressure switch in contact with the R134A ? At what pressure does it come on? I thought the FSM indicated the switch on the drier was a temperature switch.

Thanks for the clarification!

I looked at the FSM manual for 300SDL pressure switches at rec/dryer:

Freon presence switch - Off 2.0 bar On 2.6 bar
Aux fan switch - Off 15.0 bar, On 20.0 bar

Hope this help.

A Man · #22 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 · #23 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!

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