Quote:
Originally Posted by 1981_300sd
Well the reason I called them "major" issues is because one, the car runs 100% fine at idle, but when ac is on, the car shakes, sometimes dies, and is not natural for any car. I understand the 240d is not a powerhouse, but the car should not die. Especially if the car idles perfect without it on.
Oh and my idle adjust knob is not functional. If anyone knows a quick fix for that im all ears 
Even with the AUX fan on, the temp goes pretty high - I think I will change/flush the coolant as well as clean my radiator fins. |
Chances are the problem you see at idle is simply that your idle is set a little too low to start with and with the additional load of the compressor it becomes below the critical level needed to run well. You can adjust the idle and make it a little higher all the time without the adjusting dial in the car working. You may also have an overcharged system which makes the compressor work too hard (it is trying to compress liquid instead of gas). If you want to check that you'll need gauges to check the pressures.
On some models they actually had two temp switches that operate the aux fan. One is on the AC receiver and one is on the thermostat housing. Either switch, if closed would activate the fan. My W115 240D had this and so does my 560SL. I don't think the W123 did though...
I still say it would not hurt to have the aux fan run anytime the compressor runs, but it is a work-around. The PO may have put the switch in not because his temp switch wasn't working but because the car was overheating before the refrigerant temp switch was closing. That indicates a cooling system problem and the aux fan running off that toggle resolved that, at least it addressed it.
He might have a failing fan clutch or plugged radiator that's causing the car to run warm. It's relatively easy to determine which is causing the problem but any radiator over 10 years old can easily be suspect. The question is not how to fix it right, but the question is how much time and money do you want to spend on fixing it? If tying the aux fan into the compressor clutch circuit solves all of his problems then I'd do that and not look further, but if you really want to know the root cause then examine both the radiator and fan clutch for proper operation too.