Chris White

Pulling the A/C relay should turn the fans off (with the key on)...it dosen't!

Chris White

I'll check that but at first thought the resistors should only effect speed or create a non running issue.

fbgh2o

Chris

Have been thinking about this one. My experience is only with bad resistor wiring and failing switches so I am probably not a lot of help, but I assume that they have not been rewired incorrectly by someone seeking to create manual control over the fan operation. I almost wonder if it is bad rewiring?

Chris White

Bad rewiring on a 944? hmm...
Yeah, I will have to start chasing the wiring, not my favorite thing!

Techno Duck

Ill just throw this out there again..

I had the SAME exact problem a few weeks ago on my car. High speed fans ran whenever the key was put to 'on' and would turn off (no low speed, no high speed... OFF) when key was moved to 'off'. I replaced the fan switch and the problem was solved. And yes i double checked the relay (swapped it with a spare, still same problem).

Looking at the wiring diagram, check for continuity between pins 1 and 3 (high temp) on the switch itself. I bet you they are shorted together internally. and pins 2 and 3 (low temp) are open..unless of course its like 185*F out when you test it. Better yet, just pull the plug off the fan switch and the fans will stop running with the key on. If you look at the wiring diagram, the high temp and low temp circuits are completley seperate inside the switch.

Tom M'Guinn

I respectfully stand by my statement. If you jumper the first and third pins on the thermo-switch connector, the fans will not go on unless the ignition key is turned on. I have tested it personally.

Clarks-garage concurs. It says: "[t]he fans will operate is slow speed regardless of ignition switch position. However, fast speed operation is only available with the ignition switch on." It also says: "Turn the ignition OFF and swap the thermofan switch jumper to terminals 1 and 3. Turn the ignition ON. Both fans should start in fast speed. "

Also, see the schematic in the thread below, which shows the fast mode powered by a switched 12vdc source, whereas the low speed is powered by an unswitched source.

https://rennlist.com/forums/924-931-...fan-relay.html

Bri Bro

All the information is at the fan relay terminals. Just use a DVM and measure what voltage inputs are coming to the fan relay and see what voltage is going to the fans. Chris, drop me a PM and I will help you out any time. Least I can do after all the support you gave me.

Chris White

OK, I am back from the Glen and back to the possessed car….
I read the various posts (thanks guys) and I think its still possessed! I think it is pointing to a A/C on signal from somewhere.
I disconnected the fans switch – fan still comes on at fast speed with key on. Jumper 1 and 3 and the fans come on low speed (with the key off). Seems like the fan switch is good.

Next round of ideas? It sounds to me like it is acting like the A/C switch is on, I am not sure where to check this without pulling off the temp controller (messy!)

Bri Bro

The AC input is on the fan relay G10, terminal name ="AC". Ever signal you will need to measure for this problem is on the fan relay terminals.

CurtP

One leg from each resistor goes to one of the fans. If you have a short in the harness that feeds it + voltage, it will turn the fan on (and hopefully blow a fuse before it melts the shorted source wire). This obviously isn't the problem since you've already tested the connection and have both low and high speeds.

I've experienced quite a few electrical anomalies with my own car that were caused by decayed wire insulation, improper wire repairs, corrosion on connectors and a PDU that would lose power in a quadrant if it was torsionally stressed (that one drove me nuts). If it were me, I'd break out the wiring schematic and start tracing circuits and reading circuit resistance.

From the surface, it doesn't sound like an issue with the AC circuit, the ballast resistors or the connections from the fans to the PDU. I'd verify the cooling fan relay operation and take readings on the relay trigger circuits. To completely rule out the AC circuit, pull the AC fuse or disconnect the HVAC head unit.

Chris White

Thanks Brian...my problem is that I am pretty sure what it is....I just don't want it to be that!
The only explaination that fits is an 'on' signal from the A/C controller - I don't like to crawl under the dash or pull out the heat / A/C controller....

I suppose I will confirm my fear at the fan relay....
Also pull fuse 17 to see what happens...

Bri Bro

Yup, that part is expensive and a pain to replace. The AC input to the fan relay doesn't go through the AC relay, it comes from the control unit directly. The AC relay controls the clutch to the compressor. Another switch that will turn on the fans is the de-icing switch. Did pulling fuse 17 (AC fuse) kill the fan?

Toolmaster

How about a frayed AC compressor clutch wire making contact with the body?

Chris White

I pulled fuse 17 (power to HVAC controller) and the fans still come on...
I will find some time to play with it later today - Brian - i just might need to call you!
Jay - I thought of that too, shorting that to ground will not trigger the fans - its a 'hot' signal.

cruise98

I think you have a wiring problem. The fans get their power from the relay. If you remove the relay, they should stop. If they do not, they are getting power from somewhere else and in order for that to happen, the wiring has been "improved". At least that is the way I interpret the wiring diagram.