My auxiliary fan stopped working, and I'm hoping someone can help me troubleshoot the problem. I know that the fan works fine, because I jumped a wire from the battery to the hot lead on the fan and it fired right up. I'm wondering if the relay is bad. Would somebody mind pointing me in the right direction (both conceptually and physically)?

Thanks!

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1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Does your a/c work?

The aux fan is triggered by the refrigerant temp switch on the a/c receiver drier. If the a/c doesn't work well, the fan won't operate.

You can test the fan circuit by jumpering the two wires that connect to the temp switch. With the key in the RUN position, the fan should operate. If it does, the fan circuit is okay.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Yes, the A/C does work. Where is the temp switch?

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

The temp switch is near the top of the receiver/drier. Usually mounted perpendicular to the upper refrigerant line.

If the a/c, although working, is less than fully charged, the refrigerant often won't get hot enough to trip the temp switch.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Just to be clear, we're talking about jumping together the two wires that plug into the lower right of the receiver drier in the picture?

Attached Thumbnails

 

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Reference the picture, yes. The two connectors that are rightmost in the picture. Disconnect them and jumper the ends that are no longer connected to the switch. Key in RUN.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Check. Jumped them together and the fan runs. Does that mean the temp switch is bad?
And if so, can it be replaced without loosing the charge in my A/C system?

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

The temp switch could be bad. But it's more likely that your refrigerant level is low. The temp switch can be removed without affecting the a/c charge. You can test it in hot water; it should close at around 125 F.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Careful with torque on reinstalling the temp switch. It's soft brass and breaks off easily. Yes, BTDT. Snug, for good temp transfer; not uber-tight since in this model it doesn't seal the refrigerant.

Note: I just checked the Fastlane parts ref and it doesn't look correct for your model. It your aux fan temp switch turns out to be bad and you're buying, confirm you get the correct part - most likely a threaded fitting with about a 6" pig tail and two spade connectors. I think there's also a diesel temp value and a gas temp value for W123's. I forget which is lower. You can check on STARTEK. I think it posts the closing temps for the switch.

I can't speak for your present weather, but on my '83, the auxiliary fan will only work on a hot, humid day with the car standing still. I am running R12, that may make a difference.

The auxiliary fan relay is in the black box, on the driver side fender, in the engine compartment. There will be two relays there, one for the AC compressor and one for the fan.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Got it. Thanks everyone. I have two questions. Do I need to be worried about taking the temp switch out (i.e. breaking it off)? Also, is there a way to check and see if the fan relay is bad?? Your help is very much appreciated. I'm preparing for summer. . .

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

Yes.

You already confirmed that the relay is good. You jumpered the temp switch and the fan worked.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Oh yeah. . .thanks!

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

So, the switch works. I have a cup of hot water and a continuity tester sitting in my kitchen, and when I drop it in, it lights up. But, at what temperature should it come on? Right now, we're at about 150 degrees. For some reason, I'm think that it should be at about 120. . .

__________________
1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks