DanielD

I've done the search function and have come up with nothing on this particular problem.

Here's the symptom: The passenger side engine cooling fan works, the driver's side does not. Both fans are good.

The controller cycles through its normal 20 second routine and the flaps adjust as does the passenger engine cooling fan speed then it goes back to full speed.

I swap pins 6 & 8 in Plug I on the controller the inop fan stays on the driver's side. As pins 6 & 8 appear to be the controlling voltage for the fan amplifer I would think the problem would change if the controller were putting out bad control voltage. By the way, the control voltage is way high, about 17v on the meter on the driver's side fan control; it's about 9v on the passenger side. When I swap pins the high voltage stays on the driver's side.

I have about convinced myself that the dual fan amplifier is bad. Does anyone agree/disagree?? I don't want to have to buy one to find out I am wrong... I want better odds!!

Thanks,
Dan

Mrmerlin

it pretty easy to swap the fan plugs if the swapping makes the DS fan work then you have a open or cut wire to the DS

DanielD

Each fan operates normally when connected to the passenger side plug. The driver's side plug will not power either fan.

dr bob

Check the connections at the positive post at the battery. Two of those aux wires power the fans. Remove them, clean wth a small wire brush until shiny. Clean the bolt, the contact face, the washer and the nut. The snug the bolt up well.

There are separate fuses for each fan. 28 and 29 on my car. Look at the fuse holders when you pull the fuses to check for burned/melted/distorted plastic. Taking a cue from a related post on battery drain, remember that you can check for system voltage drop with a meter right on those fuses.

Last but not least, the two fans use separate power FETs in that driver unit on the front apron. A couple I've seen have failed on one side only. They are repairable if you have patience. soldering skills, and a good electronics store handy. Otherwise there are replacements around from the Usual Suspects.

DanielD

Ok dr Bob, I'm down to cleaning the battery terminals. They look good but I've never "taken it all apart, cleaned and put back together." After that I'll see if I have a voltage drop across the fuses. If not that, I need the part numbers of the FET's in the amplifier/driver box. I ohmed them out this afternoon and did not see anything obvious but maybe it is failing under the load of the fan.
Do you have the part number of the FETs?

Mongo

Are there 2 separate relays that control the fans or one big one? Sometimes a terminal or pin in the relay fails to carry over the current.

fraggle

I'll be watching this thread carefully, I think one of my fans is intermittant.

DanielD

I cleaned the battery posts and the attached connecitons. There are several.
I removed the ground strap and cleaned the cable attach point with a wire wheel so it shines now. I also cleaned the ground attach point on the car.
Everything has been reassembled and still no fan.
I checked the power for each fan at the plug on the fan amp and all is well.
Still no driver's side fan with everything hooked up properly.

Mrmerlin

OK so you now know that the DS fan wire has a cut in it,
it could be at the fan plug or where it attaches to the fan shroud look care fully along the wire harness for damage

dprantl

My passenger fan was intermittent last year. It turned out the wires on that fan plug were all messed up. I fixed it up and no more fan problem. Did you check the fan plug and the first two or so feet of wiring after the plug?

Dan
'91 928GT S/C 475hp/460lb.ft

dr bob

Ok--

With the car running and fans -supposed- to be running, use your voltmeter from ground, and measure voltage on each leg of each of the fan fuses. They should read very close to battery voltage on all four test points, negative meter lead grounded. The challenge of taking readings at the plug on the finned box is that you can't test for voltage under load. Even a tiny bit of continuity shows up as full voltage there with the high-impedance meter, so testing at the fuses under load will help you find out if it's a problem in the supply side.

I don't have the FET data handy, and won't for a while. Maybe someone else will pop in with the info. If you have the links to Theo J's tips page, IIRC he has them listed. They were a few dollars from the rack at the local Fry's when I bought them.

Mrmerlin

or better yet disconnect the fan plug on the DS and connect a test light see if you have a light come on when the fans are kicked on

Remove the front harness plug from the radiator (on the front driverside lower) and then turn on the key this turns on the fans. I still think you have a broken wire or plug to the DS fan harness its probably in the harness under the hood starting from the where the harness connects to the top of the fan shroud

jthwan22

The 2 fuse location for the fan on my car look cooked, burned. I stuck a circuit breaker in those locations. Can you put a relay for the inop fan and use the working fan signal to turn it on?

dr bob

Stan--

Still no load on the circuit testing at the open fan connector, but maybe good data. I don't know if the FET will turn off with no load.

JT-- A relay would be OK, except that the S4+ fans use pulse-width-modulated power for the fans to get the multiple speeds. I'm not sure what 'speed' would cause a relay to pull in. Plus you need a power source for the relay/fan.

OP has an option to borrow a local controlller and just plug it in, or take his controller and try it in another car.

leadfoot

The FETs (field effect transistors) of which there are 4 total I believe, caused the pass side fan to stop working in my 1987. Pss side fan worked fine when plugged into the other fans connector. I replaced the BUZ11A transistors on the cicuit board for the fan amp located in front of the rdiator pass side (all 4 as I figured if one went the others were not far behind) and the fan worked again. $2.49 a piece. i found them at www.bluestar-online.com.