Mark Stahl

Hi, everybody-
I recently went through all kinds of trouble to get my A/C working, but with the help of this list I finally managed to enjoy a nice cool ride. For about 10 days. Did the relay trick on the control head and eventually got working AC, working blower fan, etc. Took on 2 long trips and several short ones with everything OK. No strange noises or sudden changes in fan speed (signs of impending blower failure, I've heard).

All this happiness must have angered the 928 gods.

One day I get in the car, start, and turn the fan to high. Nothing. I dial it back through the settings- 1,2,3, etc-- nothing. Switch the controller to defrost-- nothing. So I check the fuse. Ah-ha-- fuse is blown. OK, I pull the fuse. Well, the fuse itself was slightly melted along one side, and when I pulled it there was some discoloration of that terminal in the fuse panel (uh-oh.) When I replaced the fuse and turned on the fan I got-- nothing. The new fuse didn't blow, just nothing at all. Switched the relay with the working horn relay- nothing.

So what happened? Is the wiring damaged in the fuse panel or between the panel and the blower? And what could have caused that? Was it related to the control head repair?

Most importantly, how can I attack this problem? I have no idea where/how to trace that circuit. Do I have to pull the fuse panel? (UGH!)

Thanks for any thoughts.

-Mark
86 928

Garth S

You may have to tilt the fuse panel down to verify absence of burnt wires - but start by cleaning the fuse slot contacts ( '86s have plug-in fuses vs bullet types .. ?).
If that goes OK, try the defrost mode and econ mode to see if the fan kicks in. The next easy test is to run a fused jumper from the 12v post underhood to the fan directly - there is a single large wire that can be disconnected under the hood on top of the blower. If it works, then the search begins between the two points with a multimeter.
In most trouble shooting exercised, it should begin with " what did I 'fix' last?" .... the controller head may be guilty.

Mark Stahl

Thanks, Garth. Do you know if the control head *could* be responsible in some way?

Garth S

I take it that the repair was for the relay that activates the AC compressor clutch - so, no - there is not a direct link; however, a lot of wires are in reasonable proximity to the fan control ....
Ron H had a recent thread on a failed controller issue, with good expertise pouring in.

Mark Stahl

Yes, it was the relay fix. Interesting that there's no 'direct' link, but of course I wonder. Will definitely look up Ron's thread, thanks!

Mark Stahl

So I swapped in a known good A/C control head-- no help. Also checked behind the fuse panel for any obvious burned wires,but saw nothing. The A/C light still doesn't come on when I press the button and there's still no blower under any conditions. I'm out of ideas. Anyone have any?

-Mark
86 928

wds928

Mark, does your model have a relay X? I had a similar problem when I would press the a/c button and get nothing, no blower fan, nothing. I also had no electric cooling fans nor fog lights either. Thought at first it was current related to the electric cooling fan controller, which was partially true.

The final analysis was a worn out Relay X, which is the same as the fuel pump relay too, the most common. I replaced it last week and haven't had any problems.

docmirror

In post #2, Garth mentions the wire directly to the blower, and testing with a 12V jump wire. This is an excellent idea, as the wire feeds directly to the motor. If you use a wire from the jump post on the pass fender, up to the blower connector, the blower should run. make sure you connect the jump wire to the + side of the motor connector, and that the motor case side is still grounded.

Another good test while you are in there is to have the wire off the blower motor, turn on the car, turn on the blower dial, and check for 12V at the wire. This will tell you if the control head, blower dial, sliders, fuse, and relay are working. If no 12V at the wire, work backward to the fuse board.

Where you plugged in the new fuse is also a good point to test for 12V when the dial is set to high.

Doc

WallyP

First thing to check is to look for 12 vdc on terminal 30 in the socket for Relay X, the Blower Relay.

Fuse # 17 feeds both Relay X, the Blower Relay, and Relay VIII, the Defrost Relay. This is one of the few points where a single failure will kill the blower on normal fan operation and on defrost operation. I suspect that you aren't getting power thru Fuse #17.

Mark Stahl

Thanks, everyone. I did swap relay X (blower) with relay XII (horn), and the horn works in either case. The fuse 17 issue sounds most likely of course (it is the one which was melted!). Obviously I replaced the fuse, but no luck. I then tilted the fuse panel forward and looked as best I could at the wires leading into fuse 17, even pulling one off.... but they looked OK. Let's say there's no power there.... then what?

the flyin' scotsman

Mark............attach the ground lead of a multi-meter to a know good ground in the fuse panel area, switch the DVM to DC volts and use the red lead to probe the fuse panel. Look at both sides of fuse 17 for power, +12v with the ignition on. If power is there re-check/replace the fuse...........if no power then you have a open in the circuit elsewhere.

Let us know.

Mark Stahl

I just wanted to thank everybody who chimed in with helpful advice and wrap up this thread for future reference. I finally (!) had time this weekend to dig into the fuse panel. Using SharkSkin's website with its great photos (thanks!!) as a reference, I got over the intimidation factor of the rat's nest known as the back of the fuse panel. Once I got in there I could see that the contacts on fuse 17 were blackened and somewhat corroded. Since I was in there, I pulled all the fuses, hit them with an emery board and some contact cleaner, and reassembled with new fuses. As soon as I did, the central climate control unit came back to life and has been working fine ever since.

I have to say, as an aside, that the fuse panel is not as hard to work on as it looks, and while the corrosion really wasn't awful I certainly feel better having a cleaner board. It was getting pretty late or I would have gone after all the relays too (next time, I suppose).

-Mark
'86 928S