87 T124: A/C works too good... - Page 2 - PeachParts Mercedes-Benz Forum

Bio300TDTdriver · #16 07-24-2010, 06:09 PM

Quote:

Originally Posted by Jeremy5848

About $23 in late 2008 according to my spreadsheet. I have the receipt somewhere. It came from a 1992 300E. The original from my '87, which I keep as a spare, has a silver sticker that says "Bosch / 12V 058 / 1 147 328 503" and then "Mercedes-Benz / 124 830 02 85 / Made in Germany." It has a Celsius temperature dial; the newer one that I installed has a Fahrenheit dial and a later revision code in its part number but otherwise is identical.

I would be willing to be wrong about the gasser and diesel versions being different but don't know why that would be so. Certainly there might be some different input connections but the ETM does not show any wiring differences. In any case, the unit now in my '87 300D came from a gasser and has worked for me since January 2009. It would also be to Mercedes' advantage to use a controller common to both gasser and diesel.

EPC indicates that gasser and diesel use the same unit and there's another thread (#278238) on this forum that discusses the same question. Several other forumites have successfully moved gasser PBUs into their diesels.

[MK] is indeed the logo for Kammerer. "Mildred Kammerer," I think. [That's a joke, son.

]

Jeremy

Jeremy,

Next time you are at your local junk yard, eh, used auto parts place would you look for one from a late model 124? I'd be happy to pay you for your time to remove it.

Chris

sixto · #17 07-24-2010, 06:36 PM

Does the compressor remain engaged if you remove one of the wires at the low pressure switch behind the left headlight?

Sixto
87 300D

scottmcphee · #18 07-24-2010, 11:26 PM

I think there is a difference between gasser and diesel units, with the microcontroller programming. I have a spare on the bench, on a sticker on the main CPU has hand written on it "6-86 TD"

Electrically the units are probably similar, but the programming is probably different. For whatever reasons.. due to difference in gas and diesel setups.

Bio300TDTdriver · #19 07-25-2010, 12:39 AM

Quote:

Originally Posted by sixto

Does the compressor remain engaged if you remove one of the wires at the low pressure switch behind the left headlight?

Sixto
87 300D

I'll check the next time it happens. It is not a constant condition.

Biodiesel87TD · #20 07-25-2010, 01:24 AM

Quote:

Originally Posted by sixto

Does the compressor remain engaged if you remove one of the wires at the low pressure switch behind the left headlight?

Sixto
87 300D

Is there a visual/auditory indication (Besides engine speed) that would show that the compresor is engaged? I guess I could just run it for a while and feel the air coming out. If the compresor is functioning correctly should it disengage with the removal of the wire?

sixto · #21 07-25-2010, 01:41 AM

Interrupting the compressor signal at the low pressure switch isolates the PBU from the Klima relay. If the compressor continues engaged with either wire at the low pressure switched disconnected, the problem is with the Klima relay.

IIRC, the PBU sends a ground signal to the compressor. If so, it could be a faulty wire between the PBU and Klima causing the compressor to remain engaged when it shouldn't be.

Are you saying you can turn the temp wheel to max heat and you still get cool air from the dash vents? If so, there's something wrong with the PBU. Heat trumps cold any day so if you set the temp wheel to max heat, you should feel the heater overwhelm AC. Any ACC mode should also respond to the max heat setting by closing the dash vents.

Sixto
87 300D

Jeremy5848 · #22 07-25-2010, 02:15 AM

Quote:

Originally Posted by Bio300TDTdriver

Jeremy,

Next time you are at your local junk yard, eh, used auto parts place would you look for one from a late model 124? I'd be happy to pay you for your time to remove it.

Chris

I'll see what I can find. Be aware that the price may have gone up in the 18 months since I last bought a PBU.

Biodiesel87TD · #23 07-25-2010, 04:23 AM

Thanks everyone!

I think it's a problem with the PBU for sure. Even though it is set to max heat and there is some change in where the air is coming out (center vents are dead), the air coming out is still fairly cold if not frigid. I'm getting a replacement tomorrow so we'll see if that cures the problem.

babymog · #24 07-25-2010, 09:36 AM

There are three part numbers for the CCU in the 124s that I know of: the early diesel, early gasser, and later cars.

I don't know what the difference is, but I have a few of each example if someone nearby (like Indianapolis for example) wants to look at a few, maybe do some testing and reconditioning.

The recall specified the Bosch units only, so it's possible that they (or likely a supplier) had a problem with their soldering process.

I don't know what the differences are, whether they are A/C related, or possibly heater related (timing of the heater start after starting the engine, aux-pump control parameters, others?). With the different engines and different plumbing in those engines, plus the small amout of heat that the diesels produce at idle, I suspect that it is heat and not A/C control that changes. Probably hard to tell the difference in operation.