Ok so today was way hot outside and got to try out the air conditioning in my new 240d. I was excited because I thought everything would go well - well I was very disapointed.

There is a toggle switch that was mounted under the dash of the car. Didnt know what it was for. I had my ac on in the car and it was getting up to 110 degrees C - I pulled over and checked things out - it turns out someone mounted that toggle swich to control the aux fan! So every time I want to cool down the car I have to use the stupid toggle swich.

Second issue - the car runs great at idle, but when the AC is on, it struggles VERY hard to the point where it almost dies. Is there something that is supposed to kick in and turn up the idle when AC is on or could it be a failing compressor dragging it down?

So basically, I would really appreciate it if someone could tell me -

1. Where do I connect the AUX fan to let the car manage its operation rather than me using a toggle switch?

2. What could be causing the car to almost die at idle when AC is on?

Thanks once again all.

Raise the idle with the knob on the dash when you're using the A/C....should get rid of the almost stalling problem. As for the toggle switch....either just leave it on when driving/using the A/C, or you'll have to look into wiring it back to the temperature sensor...which is located on the receiver-dryer unit out in the front right side of the engine compartment. Looks like a little tank with some tubes going into it. The switch is usually on there and clicks the fan on and off based on temperature. I'm guessing the sensor went bad and the owner opted to just make the fan manually controlled.

You may want to check your radiator if it gets that hot....it may be dirty or plugged or something. My temps went down by 15-20C with a new radiator....and the highest I've ever gotten it to go with the new one was about 86C going flat out on the freeway when it was about 90 outside....110C is way too hot. Mine usually sits between 80-83C 99.9% of the time.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I have heard anecdotes that a 240D running the AC will dog down. of course variables apply.
hearsay....

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

I think any vehicle you drive has to compensate for the pull of the compressor. A 240D just has less "umfff" to pull from......


BTW, I don't think your title is very accurate. These are NOT "major" AC issues.....
Actually, a toggle switch for the aux fan ain't that bad a thing. It really should run anytime the AC is on, and it does help cool the car temp some. YOu just want to make sure that there is a fuse in the fan/switch circuit.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

I agree with the others, these shouldn't be major issues. You need to un-hack the stupid toggle switch (idiot PO) and restore the correct connection to the temperature sensor. The idle speed may just be adjustment (have the valves been adjusted yet?). My 240D does idle a tad slower with the AC running, but it shouldn't be dramatic if everything else is correct.

It wouldn't hurt to just wire the aux fan to run anytime the compressor is running. If the switch on the receiver dryer is bad then he'd need to evacuate (ie recover) the refrigerant first, then replace the switch and recharge it which is a bit of work for something that really isn't necessary. He can check the switch and if it is good rewire it into the circuit, but personally, if it were me I'd probably just tap into the wiring of the compressor clutch and let the aux fan run anytime the compressor ran. It won't hurt a thing. IIRC the aux fan is powered through a relay so the extra load on the compressor circuit to close that relay should be negligible.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

That would probably work, but it's still a hack that I wouldn't live with. Just fix it.

Actually, the switch that is plumbed into the freon path is the pressure switch, which completes the circuit for the compressor. The temp switch for the aux fan does not enter the freon path. It just screws into another rec/dryer opening.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

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.

It will just just increase the wear on the fan by a substantial margin. The fan is of little benefit except in stop & go situations.

Dad has a toggle switch on his sdl so that stopped in traffic he can put it on After twice replacing temp sender sitches he determined this was the best course of action

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commercial fisherman diesel in my blood in my boats trucks and Dear old Dad has had me drivin them since i got my first license in 1968
1986 300 SDL 427654
1999 Chevy Crew Cab Dually 225423
1986 300 SDL 287000 Dad's
1987 190 Turbo 158000 Mom's (my inheritance)

Ok let me ask this - on the 240d, in traffic on a warm day with AC on, what temp should it stay below?

It probably should be about 90-95C, but my 240D gets up to about 100C (my radiator seems to be a little clogged). My 300D (with a new radiator) stays below about 95C, even on warm/hot days.

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.

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I don't believe his car has a fan clutch, but I do agree that this sounds like it could be a radiator issue.