AC was working fine, then one day it stopped. Need to get it working again.

Here is what I know:

1) I have Freon. Pressures are good.
2) Pressure switch is fine, contacts are closed like they are supposed to be.
3) Compressor is fine. If I apply 12v directly, clutch engages and compressor does its job.
4) Looking for 12V at pressure switch and not getting it.
5) Checked AC fuse and it is good

So....it appears that the signal to engage the clutch is not working. So thinking it is electrical. What else is in the circuit that I can check, and where are those components? There is probably a relay somewhere that I can test. What else?

__________________
Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

I am not remembering when the cut off for the servo ACC system is but if you have the "newer" ACC system with the push button unit...

You might have a problem in the push button unit. They are prone to cold solder joints.

Internally it is similar to this:
126 830 02 85 W126 First Gen Climate Control PBU - Imgur

The system is a three piece setup
1- push button unit (above)
2- temperature regulator unit (000 822 09 03 - 126 First Generation Temp. Regulator - Imgur)
3- blower motor speed controller ( 000 822 11 03 - W126 First Gen Blower Speed Control - Imgur)

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

No, this is not a pushbutton unit. It is the older style with the three dial knobs.

__________________
Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

Anyone else able to assist with some basic troubleshooting on the control circuit for the AC on an 81 240D? Actually, the best thing that would help me is a wiring diagram, so anyone out there have a copy that could be posted here?

__________________
Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

This document/website should have the items you are looking for:

Untitled Document

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Thanks JamesDean, those wiring diagrams were exactly what I needed. Discovered that there was a lead from the temp knob/switch that was not plugged in, and it was preventing the control circuit from kicking the compressor on. Also, looks like my charge is a little low, so once that is taken care of I think I am well on my way again.

__________________
Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K