I'm trying to get the A/C working after replacing the evaporator core last fall. Summers in DC are just too hot not to have A/C. I've got everything together and decide to stick with the R-12 based on the threads on this board. Take it up to an A/C shop and they tell me that the Auxiliary Fan doesn't come on and that, after putting 1 lb. of Freon in, the pressure gets too high to proceed. They indicated that there must be a blockage in the lines.

I've done the following:

1) Visual inspection - there is a small kink in the hose which sits near the aux. fan, (which I missed when changing things out), but that hose has been that way since the car DID have some cooling.
2) Did the check that the CD gave on the freon pressure switch. Got 15V on one terminal, nothing on the other. The CD indicated that was either a bad switch or low freon. OK - I know the freon's low, so this really didn't help.

I know I need to troubleshoot the aux. fan and fix that first. My question is - is the aux. fan problem enough to cause the pressure to go too high to proceed? I'm trying my best to avoid having to void the system (and its $70 worth of Freon I just bought) in order to fix the problem.

Are there any other obvious checks I need to do to try to fix this with minimum grief? In an ideal world, I'd find that the aux. fan relay needs to be replaced, then I could shoot more freon in and the world would be good again.

Thanks for any insights you might have on how to proceed from here.

__________________
1987 300SDL 265,000 mi.
1982 300SD 325,000 mi. (and holding)
1956 Packard Clipper 150,000 mi.

You can check the operation of the auxiliary fan by unplugging the wiring and applying 12V directly to the plug. If it does run manually and does not come automatically, make sure the engine is hot enough (may take 20 minutes of idling) you could have a bad coolant temp switch or relay. The auxiliary fan is designed to only engage at an engine coolant temperature of 212 degrees as well as a refrigerant temperature of over 140 degrees. These conditions are usually met when driving slower like around town, not on the highway when there’s enough air movement to cool the engine. A brass switch mounted in the thermostat housing measures coolant temperature. Normally the car is supplied with a 212F (100C) switch, but this can be changed to either a 194F (90C) or 230F (110C) Part number for the 90C is # 006 545 36 24.

I don't believe the fan's operation would limit your freon charge.

Sorry I can't answer your other questions.

How do you get to the evaporator?

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David Drum
Topeka, KS

On a hot day pressures can easily get too high (400psi or more) while charging if the aux fan doesn't come on.

The 82 300SD aux fan is only controlled by the drier switch at 126deg F. No engine temp component.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

dcdrum and Steve,

Thanks for the feedback. I'm going to go through the aux. fan checks and get that working, then I think I'll take it back and see if that solves the problem before evacuating.

dcdrum,

The evaporator is the biggest pain in the butt job I have ever done on a car. The car appears to have been designed around the evaporator. It's the black box under the dash, behind the center console. I had to remove the console, dash, and basically take it down to the firewall before the evaporator came out. The car looked like a bomb had gone off inside it before I was finished.

But nobody in this area wanted to replace it, and it would have cost thousands if they had.

__________________
1987 300SDL 265,000 mi.
1982 300SD 325,000 mi. (and holding)
1956 Packard Clipper 150,000 mi.