dlpalumbo

On occasion I have noticed that both my AC and oil cooling fans will come on for no reason: AC is off and oil is not hot. They come on at the same time. I have heard that turning on the AC will start both fans. Toggling AC button has no effect.

Any suggestions as to what might be the cause?? Does a single relay control both fans?

I am asking because my battery was dead this morning and my suspicions have turned to fans initially.

Thanks for help,

Dan

Zingari

Each fan has it's own identical relay so they are wired separate.

When you say the fans are coming on is that in low or high speed as high speed pulsing is usually a sign your ballast resistor is shot but I wouldn't expect both to do it at the same time?

Sounds like you have a battery drain somewhere so I'd suggest measuring the current drain when everything is switched off and dependant on what you get pull both fan relays to see if it makes a difference.

dlpalumbo

I was wondering about 1 or 2 relays for fans. I'll have to run diags to see whats what. With both fans coming on I'm thinking it might be the CCU.

Can the fans run when the key is off?? This is what I was thinking might have caused the drain, but my experience is the fans stop when the key is off.

Tried to measure drain after charging battery. Had VOM on 200 ma and popped fuse. When I connected battery there was a motor that ran and I could here a bunch of other things initializing so initial draw could quite high. I guess.

Thanks for the help.

Zingari

ToreB is the expert on matters connected with the HVAC and associated items. He usually frequents the 993 folder so might be worth dropping him a PM to contribute for wider sharing?

dlpalumbo

Will do.

ToreB

There might be limited diagnostic features in the 964 CCU. It could be a damaged relay driver or two in the CCU. However, it is unlikely that two driver IC's give up the ghost, the condenser and oil cooler fan drivers are on separate chips in the CCU.
Is it low or high speed that activates on the two fans? A good start would be to check the output signal from the CCU when this fault is active. This could be measured on the relay socket or CCU harness connectors.
Cheers,
Tore

dlpalumbo

Tore,

Thanks for input on CCU internals. I had heard the AC switch turned on both fans to high. I was thinking that the fault might be there somehow.

I assume the fans are on high speed as they are roaring.

Do you know if its possible for fans to turn on when key is off?