Hello all,

Have a 1986 300SDL with a problem that has been getting worse over the last year.

Heater, defrost, etc all work fine. The correct pods open & close so the right vents are working at the right times.

A/C is flaky. Once it starts, it runs forever. Otherwise it won't run at all. Happens at any time (car cold/hot/etc). The compressor just doesn't kick in.

I've jumped the low pressure switch with it not running, and that didn't start it up.

Here's the weird thing.. I can make it work by doing the following:
1. Push the DEFROST button (far left button). This always gets the compressor running.
2. Push the BI-LEVEL button (next one to the right)
3. Push the middle button (can't remember the name, but it's the one that runs the A/C. It's not the ECON button)

By doing this, I can usually get the compressor to start (and stay) running. Sometimes I have to do it 3-4 times, and sometimes it won't work at all (although that is quite rare).

I'm guessing I have a climate control that needs to be resoldered? Doesn't it sound like the circuit that engages the compressor is flaky?

I thought of other pressure sensors in the A/C system (compressor speed sensor, etc.) but I don't think it's those. The compressor speed sensor would shut off the A/C until the car is restarted, but I can usually get it running again. Since my method above gets the A/C working again, how can it be a sensor?

Any thoughts before I take apart the climate control unit and start resoldering?

Thanks!
Neal

PS. Is the "late" style W126 climate control the same in every car? Have seen some 1989-1991 560SEL climate controls for sale and they look exactly the same. Can I buy a good one & swap? I'm talking about the late style with three black buttons on the right side (high fan, AUTO, low fan) not the early style (high fan-black / autom.-clear / low fan-black)

__________________
'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

Yes, there is a thread on re-soldering the CCU. I had done this on my SDL and it worked for a while I bit the bullet and bought a reman'd CCU (fortunately ours is not the pricey ones). The CCU lasted 18+ years, guess I can't be upset over that.

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BENZ THERE DONE THAThttp://www.peachparts.com/shopforum/...c/progress.gif
15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

If you wish, you can perform some testing with the Klima relay disconnected. If you monitor the single pin from the PBU, you can instantly determine if the PBU is the culprit.

The pin is a ground connection. The PBU provides the ground to engage the relay inside the Klima.

LMK if you want to perform this test prior to taking the PBU apart. I'll look up the details of the pin.

Neal

Brian's comments are right on.

The low pressure switch is in series between the ACC and Klima; I would check for ground at the low pressure switch when calling for AC. If none, I think the ACC pushputton unit is the culprit (barring a wiring problem, which seems unlikely).

As an aside, I had a bad Klima (and I know I everyone says these never go bad) on my '87 SDL. My symptons, however, were different from yours: A/C would just cut randomly as if it were a speed sensor problem.

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5

I believe the middle button function is called Total Ventilation.

I think the PBUs are different for 86-87 and 88-91. I don't know what the difference is but some places list different replacement part numbers.

Sixto
87 300SDL