So my new to me 87 five speed, working on getting the A/C working, Up on the rack yesterday looking for a place to put in a compressor relay. Noted even though the engine was cold as soon as I switched the car on the fans came on. Now the A/C button was not on and as soon as I cranked up the fans came on and run all the time. with the A/C off shouldn’t the fans be on a temp switch? Also if the temp sensor fails does it fail to closed?



Dan

Just found an electrical schematics on eBay, ordered.

 

Stand in front of the car with the hood open, then look down at the bottom far right side of the radiator. There is a connector there that is probably disconnected. If disconnected the fans will always run at Key On.

 

Also, on the S4, the AC is always kept running at some level. To cool the fuel, I think.

 

No..only when the AC is on.

The intake manifold switch gone bad can do this too. Unplug it the top of the manifold to test.

 

If those easily diagnosed and inexpensive suggestions don't pan out, you may have a bad fan amp. It is the black finned thing under the hood next to the latch.

My fans at one point ran even with the key out. I had to disconnect the battery to shut them off. Kudos to my local 928 guru @worf928 for swapping a known good amp and confirming the issue. A properly rebuilt fan amp fixed the problem. The capacitors(?) fail and need to be replaced IIRC. Also IIRC, it was surprisingly expensive - hard to believe for a repair on these cars, I know. At least it was just 4 screws to swap it out.

You might want to invest in the so-called Morehouse CDs from 928sRUs. They have all the accumulated updates for the factory Workshop Manual, aka WSM, and they have a full set of wiring diagrams and bunch of interesting pics, marketing, video, etc.

 

I was just working on something similar last night but a little different. After sitting in the drive-thru on a hot summer day and watching the temp climb higher and higher until I had to switch off the engine, a later test revealed my front fan wasn't running at all - also not with the ac on. I didn't want to unplug the coolant temp sensor wires where it runs all the time as that's how the PO had it, so I decided to wire up a manual fan switch button in the ashtray. Did almost all the wiring last night.

I have a secondary fuse box installed in the car for the electrics I've added. I ran a wire from the 12v switched side past the fuse and relay panel and over to the center console. I drilled a hole in the ashtray cigar holder plate for a push button switch and ran a wire from the other side of the center console through the firewall and down the driver's side of the car to the front near the radiator, where I have an SPDT relay with a neodymium magnet attached to the relay mounting hole.

The wire from the fuse box that goes through the switch supplies 12v to the trigger wire of the relay. The #30 terminal is connected to the hot side of that radiator temp switch that gets 12v when the ignition is on. The 12v output side of the relay connects to the other wire that connected to the temp sensor switch, and I ran the chassis ground up to one of the factory ground points behind the headlight lifting bar.

Tested it last night and works as designed - just need to finish the switch wiring today (couldn't run the vacuum in the garage last night at 2 am with the kids asleep above me to suck the metal shavings from the ashtray hole out). The relay mounts using the magnet to the metal support up front and I wrapped and sealed it with stretch, thermal tape to keep water out of the contacts.

Also put the fan in with some new isolating rubber mounts (others were rock hard) and added some foam cushion to the bottom of the fan too where it sits on the body - should run nice and quiet now.

When I want the front fan to spin, I just push the button under the ashtray cover. I have my USB charger with voltage display in there too, so the door is usually open when I'm driving the car anyway

 

Petza914,So having a little trouble following you the #30 is power in and 87 to the fan what drives 85 and 86 goes to ground? Does this allow the car system to run the fan or it can only be turned on by the push switch? Does your car have a engine driven fan?
Dan

 

The relay ground connects to the chassis right at a factory ground point just below the rotating headlight lifting bar. What triggers the relay to deliver power is the new wire I ran from the engine compartment through the new push button switch. I don't know if the AC system will still automatically cycle the fan as I just replaced my drier, am waiting on a vacuum pump to arrive today so I can test and then fill the system, so can't turn that on to test it yet.

My 81 car does have the engine driven pulling fan on the backside of the radiator - this is just for the front fan.



On my supercharged 79 I have two small puller fans on the back and a larger pusher fan on the front which are all electric. These have a thermostatic controller mounted where the intensive washer bottle used to be. That setup works great too.


Extra fuse panel in front fender for heat exchanger pump, HID headlights, cooling fan controller, etc.

Front electric pusher fan with dual rear puller fans

Fan controller front left where intensive washer tank used to be

 

Finished the interior button switch installation tonight. Tested and fan comes on with the press of the button 👍