Thanks to MB Doc for replying to the previous question about a "reluctant" A/C system. Now if I can get it to misbehave long enough to pull the cover off the blower and check the signal voltage...

I indicated in the previous post that I didn't think I had any DTC's stored - I was wrong.

I checked this AM and found these codes:
43 - ECT Sensor / open short
75 - Coolant circulation pump - open / short circuit
91 - A/C compressor ground activation - open / short circuit.

All 3 of these errors are classified with a footnote #3, which indicates intermittent faults.

Other issues noted - with the temp dials set at the same position on the climate control, the temp of the driver's heater core is always 5-6 degrees higher than the passenger (and you can tell it in the temp of the air from the left center vent vs the right center vent).

Several times over the past week or so, the fan, while blowing at an accelerated level, has abruptly turned off, then back on again.

Yesterday, while trying to get comfortable (I was hot but the inside/outside temps were in the high 60's with 100% humidity) - I set the temp dials to LO. After about 5 minutes at this position, I began to smell the unmistakeable odor of cooking resin. (Worked for years at a company that manufactured a variety of high-temp fiberglass products - know the smell well). I think I was cooking my brand new Unwired Products fan speed regulator. I'll have to pull the cover off to check my suspicions. The fan speed was set to AUTO, but when I backed the temp dials down to 68, the smell went away.

The main engine harness on this car has been replaced, along with the charging/starting system sub-harness. However, the wires that go to the A/C compressor are showing the dreaded signs of insulation degredation.

The coolant circulation pump has been replaced - probably needlessly, when the climate control (before I had it rebuilt) indicated the same error. The original pump would run, but it was a bit noisy, so it would have probably failed eventually.

I'm thinking these intermittent problems are symptomatic of a A/C harness that is packing it in.

I need to do some more sleuthing under the hood on the wires that go to the ECT sensor, the coolant pump, etc. to see if I can detect more insulation degradation.

Can others shed light on my suspicions and help me drive the last nail in this coffin? The car is dark blue with a dark blue interior, I live in Houston and I am hot-natured. I'm GOING to need a good A/C when the hot weather arrives all too soon.

Most "aftermarket" blower regulators fail way too quickly..

I have replaced 100's of them less than 2-3 months after installation

The pump/heater valve codes are common & 99% of the time mean NOTHING!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

In my post I did note that I can visually see harness degradation where it connects to the A/C compressor.

If I do a little more sleuthing (I got a photocopy yesterday from MB of all the places this harness touches) and find more indication of insluation failure, I'm thinking the smart long-term solution is to replace the harness, and then worry about the other issues with the system.

Bottom line is that if the harness is failing, I'm never going to get reliable service out of the system. It will always be one thing, then another and another. Plus I'd think I risk damaging other items, like the control unit, etc, which can run into more $$$.

Not that the harness is cheap - my cost is about $1K. But I've sunk so much money into this car that another $1K is just another $1K.

The car is great and has all the indications of giving me many many years of happy service. ONCE I GET RID OF THE GREMLINS (like that's ever gonna happen on an old 140 chassis!).

While I'd love to own a 600SEL, I'm glad I've got the "bargain basement" version of this car - no ASR, no fancy suspension, etc etc - so nothing to give me trouble.

I appreciate your insight on this - if I find more rotted wire, replace the harness????

Thanks!

Have repaired that 3 wire connection on MANY cars...replacement of the chassis harness is RARE.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

cool - I'll see what my detective work turns up when I check the other connections on that harness.