AC compressor intermittent

[resto108]

Put one of Rollguy's Sanden kits in my 83 SD last year and it worked great all summer. So this year when it got warm, it turned it on and the compressor isn't running. Usually, if I just leave it on AC long enough, it will eventually come on, then works normally until I turn the key off. Then sometimes it comes right back and sometimes not. I have verified the clutch is not getting power. I have verified the pressure switch is not getting power. The mode of AC nor the temp wheel setting makes no difference. I swapped an unknown temp control box from my 123, (slightly different part number) and it did start running, but was probably random. If I unplug the temp control box while the compressor is running, it will continue to run. Turned the key off and started again, compressor didn't run. So I don't suspect the temp control box. Any ideas?

[SD Blue]

If you're not getting power at the Low Press. Cutout Switch, it may be an intermittent F11 or Compressor Relay isn't engaging due to a problem in the Pushbutton Controller or the Evap. Temp. Regulator. Attached is a pdf with the electrical diagram for the clutch on page 307. Most of my intermittent Climate Control problems were due to cracked solder joints inside the Pushbutton Controller. The circuit boards are arranged in an "H" pattern and the joints crack where they meet. Look for pics with a search of "resolder".

https://www.startekinfo.com/StarTek/outside/12253/program/ETM/ACC83-85.pdf

[resto108]

That reminds me, I did swap the relay with another one in the fuse box while it was running. No affect.

[kelley312c]

I had a similar problem in my 87 300d and it turned out to be the push button control unit.

[resto108]

Just to close he loop, I swapped in a 123 push button control unit that I just had rebuilt by James Dean and it worked normal. Sending the 126 unit off to him this week.

[BillGrissom]

Sounds like you might have had 2 bad used push-button boxes, but wait a month to insure it wasn't incidental, like from wiggling the cables when you swapped boxes. I have opened several, but found no cold solder joints, and even reflowed one just to be sure. There are so many things to go wrong in the climate system that it is tedious to trouble-shoot.

[resto108]

On a similar note, does anyone know the difference between a 123 and 126 push button control unit for ACCII? I looked them over pretty well side by side and didn't see a difference, other than the part numbers molded into the bottom.