Drained battery; poss. cause - fan switch

wwdwgs · wwdwgs's Garage

Hi, guys. I just want to confirm with you my thought.
I discovered that the battery is dead. the car was parked for 3 weeks.
I noticed that the fan rotary switch was on 1-st position. the ignition key was in the lock, but in OFF position.
Is it possible that with the key in off position the current is still supplied to the fan switch (not A/C)?
If so, stupid me, leaving the key in.

Fast Freddy 944 · Fast Freddy 944's Garage

I know my 951 fans cool my turbos after a nice drive, and my fans stay on for a few minutes to cool off the works. Leaving a key in the ignition turned to accessory or even a click above could drain a battery. My car has issues with its votlage regulator being worn out which causes my battery to really drain quickly. Pull your battery and have a shop test it. good luck..

mytrplseven · mytrplseven's Garage

If your fans run for over 5 minutes after engine shutdown, then you probably have a bad temp sensor/switch in the radiator. I had one that failed and after a great day at Disney World, getting a jump start in the dark was a pain. As soon as I started the car with the a/c off, the fans were running so I knew what the problem was.

Dan84944 · 01-06-2021, 07:53 PM

You should go take a look at my guide for replacing the switch from the top! It's less time consuming, and lets face it, nobody wants to be under a 37 year old car for that long...

dme · dme's Garage

Isn't he talking about the rotary switch for the cabin fan and not the radiator fan?

jcommin · jcommin's Garage

Dan,

I believe you are correct. The switch on the radiator can get stuck open and drain the battery. It has happened to me.

The OP speaks to the fan rotary switch. I have a 83 944 and if the rotary switch (I'm presuming for the heater)and with the ignition off,the fan stops. ( same as the AC rotary switch).

dme · dme's Garage

Short answer, if the key is off then there should be no power to the interior cabin fan. You could have an old battery or possibly some other power drain (been there). I'd start by testing the current draw on your battery with the car and all accessories turned off and definitely the key off and out. Instructions on request.

One last thing, these cars have had a lot of hands touching and doing unmentionable things to them. You'd be surprised how PO's can really screw up the wiring.