I'm having thoughts of putting the AUX fan on a thermostat, so it runs when needed, instead of continuous. Any thoughts why not to do this, would be appreciated. '83 300SD/617 . I feel the AUX fan should come into play anytime the AC is on, and any time the water temp exceeds whatever value you choose on the adjustable thermostat. Especially for our cold climate. Thanks.

That is the way it is supposed to work... is your on continuously?

Is there a way to test the fan? Mine has yet to come on (I have only had the car for 3 weeks and no warm weather yet). I would like to test the functioning before it is needed and leaves me on the side of the road.

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Fantom71 aka Dale
Madison, AL

91 190E 2.6 5 speed 220k miles and this car still scoots!

The aux fan should come on when the AC is on or the engine temps reach a specific temp, normally that only happens during the summer months. There is a temp sensor that can be modified to turn the aux fans on earlier than normal, this is what I did.

Here is some info, although it may not apply to your specific model

http://pages.prodigy.net/jforgione/MB_CTS.html

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1993 500E
http://2phast.com/500e/500e-sig.jpg

Al,

On your 1983 300SD only the high pressure of A/C refrigerant will trigger the aux. fan. There is NO thermal control of it on your car, unless you add it.

On later (I think 85) models there is a sensor on the thermostat housing to trigger it thermally and this is where i drilled and tapped the housing to hold an electric fan regulator sensor wired then to a relay to turn on the aux. fan.

The electric fan kit is available from Spal, Sun pro and some others.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Jim H, yes mine runs all the time. I'm thinking someone has fudged it to run continuously. I didn't realize it wasn't supposed to be this way, but thanks guys, I'll go find where the glitch is. I did see a 15amp new style fuse plugged into the harness down near the glow relay. I'll pull that fuse tomorrow, to see if that's what is powering the fan. Jbaj, where is that switch located?

The swich for the aux. fan is on the receiver /dryer. It has pigtails.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

I thought that was the case. The fuse must be jumping current in the plug that normally plugs into the switch. Maybe the switch was bad, and this is someone's cheap fix. The car is new to me, as of a couple weeks ago. Thanks again, I'll eyeball it tomorrow.

OK, did some checking today. Can someone tell me how many electrical switches/senders belong on the Receiver dryer? The wires I spoke of earlier, are in fact the two that plug into the switch on the receiver dryer. Light brown or tan wire( I assume in a ground, and a light brown or tan wire with a light blue chaser. Both of these wires have the female mate to the aux fan switch pigtail, if I had a switch. There is already a switch on the receiver/ dryer, that is not configured properly, to mate with an aux fan switch pigtail. One of the fitting bosses on the receiver/dryer has a port plugged. Maybe this is where the aux fan switch belongs? The receiver/dryer is brand new, so anything is possible. I pulled the fuse that was jumping, and that killed the fan.

On the 83 300SD there should be two switches on the R/D.

One (black with two prongs) is a low pressure cut off switch to protect the compressor should refrigerant leak out.

The other is typically red (although green, a different pressure setting, is also available) with pigtails coming of it. This is the switch that turns on the aux. fan when the high side pressure reaches a set amount. It sounds like the P.O. did not insert this switch into the new R/D, but merely jumpered the two wires to it, keeping the aux. fan constantly on. ?

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Thanks for the comfirmation. He probably charged the system, then realized the switch was forgotten in the old R/D. I'll get a new red switch, and do it right!