Strange 280C AC Problem Solved

[ctaylor738]

If we ever have a thread with "Dumbest Things I've Ever Done to My Car" as a topic, I will also post this there.

Decided to tackle the non-functioning AC in the 280C this week. The system was working a couple of months ago, so I thought that I had knocked a connection loose when I took the console out to hook up the radio and speakers.

So I pull the console back. Everything looks to be connected. I try the switch. The vacuum gizmos close the flaps and appear to actuate the cutover switch. But the AC fan will not come on and neither will the compressor.

Check the schematics and determine that source of power is a 16A fuse mounted on the firewall. Fuse looks good, getting 12V in, 12V out.

Remove cutover switch and bench test. Works flawlessly. When AC switch turned on, Pin 2 receives power from the 16A fuse when the blower switch is turned on. From Pin 2, power goes to the blower motor via Pin 6, and to the compressor clutch and the little green light via Pins 1 and 5 respectively.

Verify with switch out that Pin 2 gets 12V with ignition on and fan on. Remember, Pin 6 sends power to blower. Jump Pin 2 to Pin 6 and, after removing console completely, note 12V supplied to blower motor at connector, and that ground on other side of connector is good. So why will the blower not work?

Jump Pin 4, which gets power from different fuse with ignition on to Pin 6, turn on blower switch, and voila - blower works. Now I am really confused. The blower works with 12V from Pin 4, but will not work with 12V from Pin 2. Does it not like Pin 2's power?

Perform various other tests to insure it's not the ground etc. and conclude that Pin 2 must have poison power, because the blower will run on anything other than that feed.

At this point I go back to the fuse, and discover THAT IT'S NOT SEATED CORRECTLY IN IT'S LITTLE CLIP! ONLY THE POINT IS TOUCHING THE FLEXIBLE PART! I re-seat it, cleaning it and the contacts for good measure. Miraclulously, the blower now likes the power from Pin 2. Start car and both compressor and blower work. I have AC!

Conclude that the poorly-seated fuse supplied enough voltage but not enough amperage to run blower.

Feeling like an idiot, spend next hour re-installing cutover switch, console, power window switches, etc.

Moral of the story - look closely at the simple stuff first!

Long time no hear. Glad to see that your skinned knuckles has paid off. Sold the 230SL and replaced it with 2002 320SLK and after that, a 1982 240D (for the bad days).

Cheers.....Say hi to the boss!!