Cabin Fans Mystery...

[fleetline51]

So...Here we are, cruising down the highway and enjoying an unseasonably warm
afternoon with the top down( '90 C4 Cabriolet). Everything is purring along just fine,
and then we "bumped" a high spot in the road expansion joint and the cabin fans come on by themselves.I did not have the fan switch on,nor did I have any of the
accessories energized.The strange thing is that I have been trying to figure out why
I can't get the cabin fans to come on with the air conditioner or the heater...
I bought the car that way about a year ago and can only get the fans to function if I jump out connections at the amplifier mounted on the large aluminum heat sink mounted in the front "trunk" stowage compartment. All fuses,relays and resistors are good, and as far as I can tell the plug-in connectors are functional.

The question: Why did it come on when we hit the bumps(stayed on for a few minutes the first time we hit a bump and again when we hit another bump)then stopped.I never had cabin fan control via the dash switch...just never worked.

The a/c compressor works and the system blows cold air when I jump out the cabin fans and get them blowing.The rear blower in the engine compartment works,but then again,only when I jump it out.

I would LOVE to get the system "functional" againg so that when I sell this beauty
some Idiot will not try to beat me up over sale price!

Any help will be greatly appreciated!

Much Thanks!

Tony

[zajo]

I have a similar problem, '90 C2 Targa: when I got the car a year ago both heater and AC worked fine, then recently the fan went crazy: if I leave it at 0 or 1 it would go all the way to 4 on its own (with the knob still at 0 or 1) and the way to turn it off was to put the knob at 4 then rotate it back to 0. It did this for a couple of months, then stopped working altogether.

With what you're saying, I bet that if I jump out the fan everything will just work. So I'm also hoping someone will help here!