How do you know your fan is fried? It could just be the thermoswitch needing a replacement! Unplug your fan and connect the leads directly to the battery just for a second. If it tries to start, your in luck! A thermoswitch is cheaper and since your AC has no refrigerant (most likely) easier to install! It's on the refrigerant gas dryer on the left side while standing in front of the car. It's about 3 inches in diameter, up to 10 inches tall and will be black with a few wires attached to it. There is a pressure regulation switch which keeps your pump from turning on if the refrigerant escapes, with most likely 2 wires on it and that part will be a little larger than the thermoswitch which turns the fan on when a certain temperature is reached. The pressure switch will be mounted on the side (wide part) of the rectangular little box on the reciever/dryer top and the thermoswitch will be mounted on one end (narrow part) of the rectanglular part. There should be a little dimple on top of the rectangular part, this is called the sight glass and most have them. Jumping the 2 wires on the pressure switch will turn on the compressor when the engine is running with the AC controls on, Jumping the 2 wires together at the thermoswitch will start the fan if you AC has been turned on. This is only to be done momentarily to confirm your electrical system for your AC is ok, OK? Your Haynes Manual should have a picture of this. When you add refrigerant to the system, you watch the sight glass and when it looks like the foaming/ bubbles are about to stop, your system is near full! This is a rough description, but for basic principles, it's a good way to understand how some of this works! Let us know how you get along with this, OK?

wow. thanks for the info. unfortunately, though, i meant that the fan motor seems to be burnt out, as its basically rocks solid, and nearly impossible to move!

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1982 300sd, 230,000 miles, svo/wvo conversion... yellow

http://www.jaymoschella.com

Your right, not a good sign, but it is cheaper and easier to replace than a compressor!!! HA HA! Hopefully your compressor will be ok! I'm almost willing to bet the fan burnt out and someone cut the belt either because they didn't understand how to go about making repairs or just cutting the belt off was simpler! Lucky for you if the latter is true! Boston may be cold in the winter, but it gets hot and muggy in the summer. I used to live there! I did see some reasonably priced fans on ebay. Check it out, you could get kinda lucky in all this!

So far no one has mentioned transmission cooler lines. Does this car have them? I've swapped radiators a couple of times on my '80 300 TD, and found these two lines connected to the bottom plastic tank of the radiator. The first time I got them off and on again without problem, but the second time I managed to twist loose the nipple on the tank. I was going to replace the radiator anyway, but I didn't like breaking stuff that way. Any suggestions ?
Steve

Yes, grasp the fitting on the radiator with a thin wrench or vise grips if you have to. There should be a spot on the fitting where both sides are flat for this, but your wrench will have to be thin and this is best removed from the bottom. I sure you know that if you break the plastic, you are screwed! The threads on the fitting are tapered and will be on a new radiator as well providing your new radiator comes with new fittings! Most do. You need to grasp the fittings with your wrench especially when tightening your cooling tubes from the transmission to it! Be Careful, this is delicate! Helpful hint.... if you can get your hands on a couple of golf tees, they made great tube plugs so all you tranny hydraulic fluid doesn't drain out and make a mess!

Considering that the a/c has no refrigerant, what circumstance would cause the thermoswitch to close and provide power to the aux fan?

If you want to just check your fan, just unplug it and jump it with a battery. I know that if everything is working that the wires to the temperature switch can be unplugged from the switch and touched together and the fan should run. But if there are any problems there might not be 12 volts at the temp. switch. But every MB I have messed with has had power to the temp. switch and even with a bad compressor or no belt the fan will run if the 2 wires are touched to each other.. I also like to unplug the compressor and use a battery to jump the compressor and see if the clutch is in working order..Jim

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James A. Harris

Heat basically! If the thermoswitch at the location I described to the originator of this post happened to be the only one, then I would think it was locked into a closed position. (Stuck on all the time) I've seen that before. Being a Mercedes Benz, I wouldn't be suprised to find out that Benz put in a failsafe somewhere, like another thermosensor. I never really thought of that before. If your fan is coming on in hot weather and cycling on when needed, then there is another thermoswitch. I do know that the one I described earlier is attached to the receiver/dryer because when a refrigerant is going from a high pressure gas to a high pressure liquid, it is giving up heat and the dryer is one of the most reliable places to find it. It will get hot in the process of doing it's job! If your fan is coming on when you first start the motor, then your thermoswitch is stuck on (closed). Are you having problems in this area?

Yep, my story too. It's been over a year now and still have a ways to go. But in the mean time it is a driver and I've learned a lot (mostly from this site). And over all she's been pretty easy to work on. All in all I coulda done much worse.

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Sonny


86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work

What is wrong with your radiator??????// Jim

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James A. Harris