I have been doing some searching on the forum, but have not seen anything specific on w126 91 350SDL. Yesterday it got up to 88 here and my AC was struggling to keep up. Car never got above 80C. My buddy and I checked the freon and with an outside temp of 80, the best I could get out of the vents was 58F. We added freon, and the temp started to come down. We noticed the cooling fans were not coming on, so we took a garden hose and cooled the condenser down with water and the temp drop down to 50F. My question is when do the fans come on, and shouldn't they be running with the AC on. By the way it has been converted to 134 and I a have been told these older MB do not alway like the new stuff.

Do the aux fans run at all?

For the aux fans to run the AC system must be properly pressurized. Check the system pressure.

No, they did not come on at all. The system seemed to be pressurized. It was taking on freon like normal.

Pressure switch for fan is near dryer. It is easy to overcharge with 134 if you are using the sight glass looking for bubbles. Recommend guages to check pressures

We were using gauges. We did not want to put more freon in until we could get the fans to come on. What should the gauges read on the high/low side to be completely charged?

What refrigerant?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

AC Kits site has ambient temp and freon pressure charts.

Have you tested the fans by feeding then 12v from the battery? The fans kick on also based on the temp of the freon at the dryer. Being 134a it would be better if the fan came on based on ambient temp and when the compressor kicks in.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I believe the cooling fan in front of the condensor (auxillary fan) should come on at low speed whenever the AC is on. Disconnect the plug for the fan and attack leads to the battery. If it turns on, you can start looking for other problems with the circuit. It's fairly common for those fans to fail.

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1976 BMW 2002- 100k
1995 BMW 325i 175k
1984 Mercedes Benz 300D Turbo Diesel- 270,000 mi

1981 Mercedes Benz 240D- Estimated 300,000+ mi Returned to the earth

Thanks for all the advice, I am going to try and apply 12 volts to the fans and see if they come on to make sure they are not fried. Then I will start working up to the switch on the dryer. Do both of those fans come on with the switch at the dryer?

Wait a minute. There are 2 switches at the dryer (if like W123 and W126). The pressure switch mentioned several times above has nothing to do with the fan or fans. It completes the circuit for the compressor if there is sufficient refrigerant pressure. {rrgrassi mentions the heat trigger}
The other switch is the one that "operates" the aux fan or fans, and it is activated by temperature, via the heat from the condenser.
I believe if not perfect, my info is at least close to accurate....

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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