LoveLEE143

1989 300E


OK so I am trouble shooting my aux fan as it doesn't work. I have search through many other threads but have not seen one with pictures. Different people have been using different names for the same part which has lead to some confusion.

First I have put 12 volts directly to the fan plug and the fan spins.



I checked with volt meter that 12v is running across the fuse in the fuse D. Which is the fuse for the aux fan.



I checked with volt meter that 12v is running across the strip fuse.



I jumped the AC dry receiver together. I get a clicking noise from the relays behind the fuse box.



I jumped the temp switch and I get a clicking sound from the relay behind the fuse box.


I tested the resistor and got no voltage. I tried jumping the wires and still got not voltage.



I am not sure what else to check. I prefer not to trace every single wire in the whole system. Thanks for your help in advance.

shadowgriffen

stupid question but -

EDIT: NEVERMIND I don't know how I failed to understand it's your "fan" not working itself...

LoveLEE143

You have confused me?

shadowgriffen

sorry I was going to advice that you change your HVAC unit for a new one, but I read that you said it was your fan, not the HVAC unit itself.

shdoug

12 volts DC ACROSS fuse = blown fuse. Should be 0 volts DC across fuse, 12VDC from both sides of fuse to ground.

I've read on here that many people replace all of their fuses to eliminate problems like this. I see there a few fuses that look like they are from a Dodge Dart in there. At least wiggle all of them around to get a good connection.

LoveLEE143

OK I put wire straight from the battery to the resistor in the last picture. If I put it on the top of the resistor then the fan spins at a low level. If I put it on the bottom side then the fan spins at a high level.

shdoug

It sounds like you've determined that the fan and resistor are good. If I have time when I get home I will look at the wiring diagram and see what else controls it. I know it can be activated by the high pressure switch on the AC Condenser. If you turn on the AC on high and compressor runs for a minute or so it should build up enough pressure to turn on the fan. If the compressor cycles off by the high limit (cutout) switch before the fan starts then that is a problem. It would be difficult to determine if the compressor is cycling on the low cutout switch, which is normal, or the high cutout which is an emergency safety switch. If the liquid line (small silver tube leading OUT of the condenser toward the firewall) becomes very hot and the fan never activates then this is a clue that the fan circuit is faulty, which you may already know.

It can also be activated by one of the temp sensors at the t-stat housing, but I THINK that is an input to a logic board somewhere. Note my signature/disclaimer.

92300E

I am not sure if your problem is like mine. My problem was that the aux fan would not come on under any normal operation conditions and the engine would heat up to near max when I sat in traffic for a while.
What I did was take off the fuse box cover lid that you open to get to the normal fuses. Then, you see two screws directly underneath the lid as well as four more a little further back towards the cabin, all of which hold down the black plastic cover that the fuse lid snaps onto. You will need to open the hood all the way for this. Then, once the screws are out, take the cover off, and you will see a bunch more fuses, all of which control the low and high power fan setting. As soon as I replaced the fuses, one of which was obviously melted through, the fan works perfectly.
I hope this helps,
Leo

rorypff

Good Day

If both relays are clicking then it could be a problem with the wiring from the relays to the aux fan resistor or the relays themselves are faulty.

The two relays are in a plastic box (remove screws to release lid) behind the fusebox.

The ac HP switch switches on the one relay which in turn conects to the low speed side of the resistor, the coolant switch switches on the other relay which connects to the high speed side of the resistor.

Trust this is of use

Eliot

When I had this issue it was the wiring.

landspeed124

Pull the fuse out and check the resistance from the output of the fuse(bottom) and the wire going to the fan, should be less than 0.5ohms. My car had the same issue and the fuse got so hot causing the fusebox to melt under the fuse pushing the terminal down and causing an open circuit. I heated up that portion of the box with butane torch and pushed the terminal back up, let it cool and then packed the fuse connection with dielectric grease to promote a good connection.

jharrisiii

Electronics 101 note on using a Volt/Ohm meter - When checking for voltage or lack of, the black lead goes to a solid ground, like a screw that penetrates sheet metal. The red lead goes to the point of interest. Handy if the black lead has an aligator clip adaptor, frees up one hand.

When checking a fuse in a circuit, black lead goes to a solid ground, the red lead goes first to one side of the fuse, then the other side. If there is power to the fuse, you should see exactly the same voltage reading on each side. If you get zero voltage on both sides, either that circuit isn't powered up (ex. key off) or the power to the fuse block is a problem. Not all fuses have power all the time and under all circumstances. Fuses are also subject to intermittant corrosion and thermal failures - it may take a particular circumstance for a fuse to stop "fusing". The act of removing and reinserting a fuse may be all that is required to reset the failure condition and "fix" the problem.

Measure resistance (Ohms) when checking a fuse out of a circuit or fuseblock/holder. Red lead to one end, black lead to the other with nothing touching the fuse except the meter leads. Should be zero ohms; dead short. Anything other than zero ohms could be a problem.

Hope that helps.