Changed out the radiator for a 928int alum one. Nice.


Now...NO fan speeds at any setting except defrost, where only THEN will the AC button light on when pressed, and I have fan control at that point only..only in defrost mode.

Huh?

 

Hard to say what might have been disturbed.
Or if the problem is related to most recent work (often it is)

Didn't you start driving this one, though, expecting to fix-as-you-go?

I don't remember you going through the cadence of pulling the CE panel for cleaning, replacing all fuses and 53 relays and cleaning all grounds.

A certain level of stability will be established by doing that, if not already done. Makes all the troubleshooting easier from that baseline.

That said, there are separate relays for stepped fan operation and defrost fan operation. Same fan, two relays and IIRC two fuses. Do you have the diagram? If not, I can pull it for you and post a piece of it.

Edit: one fuse, #17. Defrost relay is VIII. Blower relay is X. (see 928 Specialist site for map)
Pertinent ground points both inside the car: MP V on firewall above CE panel and MP IV reachable on your back, under steering column.

Maybe somebody else knows what might be important in the radiator area (where you were working) to the HVAC blower. I don't see anything.


Some pictures of the new radiator would be good. Where did it come from? How much?

 

Most likely problem is a faulty blower relay. Try swapping the defrost and blower relays and see what happens.

 

Welcome to our world... and what we refer to as 'progress': fix one thing, then figure out what you broke fixing it. These poor, neglected beasts are a poster child for the weakest link concept... it just keeps moving down the line until you've exhausted the trail of parts that lead there, or fixed PO hacked wires, or re-connected that loose ground, or plugged that vacuum leak, or applied the correct amount of lube to the right bushing... lol But man, when they're right... best GT roaming the planet.

Good luck with the electrics. The rad won't give you any more trouble, I've been running one a couple years, zero issues.

 

Did you disturb the exterior temp sensor in the front bumper? In other words, does the exterior temp display seem to be working? Cos you presumably took the lower valance off. Lack of exterior temp sensor has caused similar problems for me in other cars.

 

Nothing under the car was removed, fans out, unplug hoses/lines, temp sensor in radiator, and put it all back.

I have an exterior temp sensor display in an 88 S4?

 

No display - but there's an external temp sensor that gives input to the HVAC system - its in the front part of the driver's side wheel arch, and the harness runs down the side of the engine bay to around the radiator area.

The sensor (thermistor) is in part of the corrigated hose that feeds air to the alternator.

 

None of that will affect the blower...

 

I suggest listening to Wally here. I bet he has more people with 928 blower problems than anyone else ever in the history of the world.

 

Good news bad news..

Good news: Fans work on all HVAC vent settings, and at all fan speeds..not just all fan speeds at JUST defrost.

Bad news: Why is relay #3, windows...REALLY HOT anytime the car is on?


Tomorrow..gonna pull the switches, see if something is stuck.

 

just unplug one of the switches the connectors are at the front of the side console covers so they both must be removed.
each switch has the wires running up each side of the hump. if the unplugged switch then lets the relay be cool then you would plug it back in and then disconnect the other side
If the relay stays cool then either the relay is bad open it .

or there may be a shorting wire in the door sheath wire bundle.
The other possibility is that the switches themselves may get stuck in the pressed down position the switches may have to warm up to stick.
In that case use a dremel to reduce the outer edges of the switch rockers.
Try to push the switches up from the bottom ,NOTE there may be a plastic cover fitted to shield the wires/switch bottoms, if so then the switch will have to pried up from the top