Randy V

Recently, the driver side cooling fan has stopped working. The other one performs normally.

The non-op fan spins freely when turned by hand.

Any suggestions as to what the cause might be?

I have not yet tested for good connection or continuity through the fan.

Thanks.

Herman K

Did you check the fuses on mine I had a partial melt down on one. replaced with some external fuse holders and it has been fine since.

How old are the fans they may be draging and drawing to much current causing the melt down.

Alan

check the fuses as Herman says - then swap the fan connectors and see what happens. If that fan works and the other stops - its the controller, if the same fan is dead its probably just the motor on that fan (brushes worn out or burned out winding maybe...)

Alan

Leon Speed

Yes check the fuses. The fans do draw a lot of current and a dirty connection can cause a lot of heat. melting the fuse. Also, I seem to recall there is a safety feature when one fan motor stops working the other one blows at high speed all the time, it that the case?

Speedtoys

No..that's the radiator temp switch. If THAT fails, they blow 100% all the time.

Alan

For a fan failure - whenever the fans are needed the remaining functional one will run at full speed

Alan

GregBBRD

Randy:

Fuse, fan, or fan amplifier.

Check the fuses. Hook 12 volts up directly to the fan and see if it runs. Disconnect and spray the connector into the fan amplifier with contact cleaner. If the fan and the fuse is good, I can send you my "test" fan amplifier to plug in. The logic circuit in the fan amplifier is very clever, but can "fool" you very easily. If the problem is a fuse or a fan, you can "fix" the problem and not have both fans run, immediately. If the "logic circuit" has shut off the current to one fan, because the fan is not working, it will not re-energize that circuit immediately.

The "circuit" checks the "bad fan" every couple of minutes, to "see" if it is now functional and ready to run. You can actually hear this "checking of the circuit", when one fan is running at high speed. Every couple of minutes, that fan will slow down, while the logic circuit checks the other fan. If the other fan is then ready to work, it will "fire" both of them up, at normal speed. If the other fan is still bad, the circuit will then speed that one good fan back up.

What does all this mean? If the fuse or the fan is bad, it can take a couple of minutes for the fan amplifier to know this and resume "normal" operation. You have to be patient. Give things a few minutes.

Speedtoys

What? Then I have something very quirky. I have occasionally -1- fan working.

Other fan does NOT run full speed all the time.


*grumble*

Alan

Note what I said in detail - if the FAN fails. If the driver circuit fails it may not work so gracefully...

You should never have one fan doing different than the other except if there is a failure - so should be both off or both half speed or both full speed - never anything else

Alan

mirousse

Been there...

First run the diagnosis procedure of the service manual. Most likely you'll end up with a faulty output module.

Here's what I did and worked just fine for me.

1- Open the unit by removing the back plate
2- Replace the 4 transistors (search for the equivalent on this forum - about 25$ total at any electronic component store - also buy heat sink paste for step 6)
3- Unsolder the round plastic plug
4- Reflow the circuit board in a conventional oven (lookup "reflow computer circuit board" on google - I believe its at 285 for 12-15min - VENTILATE THE HOUSE during the procedure)
5- Put the plastic plug back in place
6- Spread heat sink paste on the metal pieces on top of the transistors
7- Put back the back plate - don't seal yet
8- Test the unit by idling the engine and wait for the fans to kick on
9- Hopefully it'll work - seal the unit with your favorite car sealant - screw back on and be proud!

mirousse

Here's the post for opening the unit and replacing the transistors

https://rennlist.com/forums/928-foru...ive-fixed.html

GregBBRD

And know that I've seen so many of these units "ruined" by attempted home repairs that I no longer will accept an "opened" unit for rebuilding. Most of them look like they got attacked with an axe and virtually 100% never get resealed completely.....so even if they do work, they "die" from corrosion within a few years.

Some things are easy to fix at home....this is not one of them.

Randy V

Turns out it is the Output Fan module, PN 928 618 421 00.

This unit is NLA, although 928 International sells a rebuilt unit - and they're not cheap.

Our Greg B. is the one who rebuilds them. My unit has not been molested so it's good for a $200 core refund.

Kevin in Atlanta

They show up on ebay all the time.

Randy V

Maybe, but not when I need one - like now.