W126 climate control flaky

[bhatt]

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)