Question about auxilliary fan not working
 

Folks, I just got my AC fixed after going without all summer, and realized this evening that my auxiliary fan didn't come on. First thing that I'll do tomorrow is to check the fuses, but the fan turns and is not bound up. This is on a 1983 300D. Is there anything else that I can do to troubleshoot this issue? Thanks so much again for your help!

Aux fan is on a temp controlled thermostat located by the pass. headlight, on top of the A/C dryer.

If that switch is bad, it's not going to come on.

Also check Fuse 14/16 in your fusebox, that controls a lot of relays.

(If your thermo switch is bad, I have one for sale cheap that I don't need)

Disconnect the two wires at the temp sensor on the receiver/drier. Then connect the two wires (the ones not attached to the switch) together. The fan should run when the key is placed in the "run" position.

The temp switch looks like this:
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2650Q36L326X0CCT0A&year=1983&make=MB&model=300-DT-001&category=R&part=A%2FC+Temp.+Switch

Thanks so much, folks, for your help. I'm going to take a look at things this morning and will get back with you, thanks again!

i leave my 2 wires connected together all summer deathly afraid of overheating

Thanks so much again, folks, for taking the time to reply to my question. I didn't have a chance today to check into the fan, as I was busy replacing the overflow tank, flushing out (as best I coulde) the radiator and refilling with fresh antifreeze and Water Wetter, then installing my ipod adapter for my new car stereo and putting everything back together again. Tomorrow I am going to try the wiring trick with the auxiliary fan and hope to change out all of the fuses for new ones. Thanks so much again!

Well, folks, I had an opportunity to look at the wires going to the receiver/drier today, and before I do anything that I regret, I thought I'd double check with you all to ensure that I disconnect and connect the appropriate wires.
I have two sets of wires going to the receiver/drier; a blue and a brown wire, going to a switch located on the top of the receiver/drier, and a green and blue striped wire and a blue wire going to a switch located more to the side of the receiver/drier.
Which set of wires do I disconnect, and which do I connect in order to turn on the fan?
Thanks so much in advance for your help and patience!

You want the one on the very top. The wires connect to pigtails from the switch, not to the switch itself. (On the other switch, the wires connect directly to the switch.)

Once the two wires are disconnected, take the two that are no longer connected to the switch and connect them together. That should cause the fan to come on with the key in the run position. The a/c need not be on.

qft, it can't hurt anything.

What's the CFM on the Aux Fan vs. the Main Fan? I feel like the main fan saps too much power, and was thinking of converting it to an electric, or getting a dual aux fan setup and just using that.

Nothing but the fan.

Well, folks, I did what you suggested, and the fan did not come on. As I placed them together, I heard a kind of clicking noise over by the fuse box, so I removed the fuse box cover, and did not see any blown fuses. Over the weekend I replaced ALL of my fuses, as I'm sure some of them were original to the car. At any rate, the fan didn't come on, I could see no sparks, and I don't know where to look next.
Any ideas or suggestions would be GREATLY appreciated, Thanks so much in advance!

The clicking sound would have been the fan relay, located under the plastic cover on the inside of the left fender well.

If you trace the power cord from the fan, you will find a connector. Unplug the connector and connect the fan directly to the battery.

Thanks, folks, for your suggestions. This evening I looked at the wiring harness on the Aux fan, and it looks as though it goes under the engine compartment under the windshield washing fluid cannister, but I don't know where the connector is to disconnect it from the rest of the circuit, in order to just connect the fan straight to the battery to isolate whether or not the fan is bad or perhaps the fan relay is bad.
Any suggestions?

Thanks so much in advance!

It would be great if you would enter your car year & model with your signature.

You will find the fan connection behind the lower cowl on the drivers side. A zip tie was used on mine to hold the harness to the cowl on the side (of the connection) opposite the fan. At least that's where my '84 location was. You will probably have to turn the front tires out or raise the car to access the connection.

And this fan is triggered on by A/C pressure not simply that the compressor engages. So, if ambient temperature is not real hot the fan will not come on for some time. It is also triggered on by engine temperature thru another circuit, so again, if engine temperature is stable within range, the fan will take forever to turn on.

Thanks, folks, for your comments and advice. I have added my 1983 300D to my signature line. I realize that it is activated by A/C pressure, and as the previous posts indicate, we are attempting to determine whether the fan is faulty or the relay. I have already disconnected it from the Receiver/Drier, and attempted to connect those two wires together, but all I got was clicking from the fan relay. The suggestion was made for me to wire it directly to the battery in order to see if it would come one, and I had to find the connector in order to do so. I won't have time between now and Saturday to jack it up and look for the connector, but I hope to do so Saturday. If it does turn out to be the fan, I found someone who is selling one for $25.00, and I need to determine whether or not it is the fan before purchasing that one.

Thanks again, and any and all other suggestions are welcome!

The fan switch is a temperature switch, not a pressure switch.

That would be factually incorrect.

The connector is a little tricky to find. It is roughly at the lower, left corner of the oil cooler. You can see it from the left wheel well. It's about the size/shape of a cigarette lighter (the old "box" style) and is just forward of the left-hand horn, clipped to the frame.

The fact that you hear the relay clicking is not a quarantee that it is working, but it's a pretty good sign. You could switch relays if you want.

Well folks, I had a chance today to disconnect the auxilliary fan and hooked it up to jumpers straight to the battery, and couldn't get it to turn, although it turns freely by hand, so I guess that pretty much proves that the fan is not working.
Any other suggestions?:confused:
Has anyone had luck rebuilding these fans? I read somewhere about rebuilding them, but don't have a source for brushes.

Thanks so much!

Well, to close the loop, I had purchased a fan on eBay, and it arrived today. When it arrived, I plugged it in, shorted out the two wires going to the receiver/drier, and it fired right up! With the help of my son, I installed it, drove around awhile, then had to let the car idle ~15 minutes before the fan kicked in, but when it did, it really roared!
Boy, that bottom bolt is a pain in the rear!
While the fan was out, I took the opportunity to examine the condenser. I couldn't believe how many little rocks and crud had gotten between the fins, so I blew out the condenser with water and air pressure, before installing the new fan.
Works great, and thanks again for all your help in troubleshooting and isolating the problem to the fan!