mwildt

Hi,

I've been trying to narrow down a battery drain problem for a while. Finally got around to investigate this further, unfortunately I forgot the actual numbers but here they are from memory:

I measured the amps drawn from the battery with all doors/lids closed.

Pulling Fuse #1 reduces the amps drawn from ~500mA to about ~30mA
Leaving Fuse #1 in and then removing the HVAC control unit completely does the same.
Just pulling the external fan wires on the HVAC control unit (leaving the 2 big connectors in) have no effect.

So I believe the HVAC control unit is the cause of the drain, or it could be any of the step-motors/fans it controls.

I found some old discussions that listed Otto's in Venice (CA) could repair these modules, however I'm open for other ideas before shipping the unit off. Is there any checks I can do to narrow this down more, assuming it's not the control unit it self ?

Thanks,
Michael
'93 RSA

Eric Kessel

Did you have anyone pull the fault codes from the controller?

mwildt

Hi Eric,

Nope have not been able to get the control codes. Good idea. I'll try to get by my mechanic to do that before sending in the hvac unit. I believe you would need the famous 'Bosch Hammer' for that.

Thanks,
Michael

Adrian

Dear Michael,
First thing to do is to pull off the fan assembly from the rear of the control unit. This does not FIX the problem but it might fix the problem. It is best to remove the fan completely rather than just the wiring to the fan itself.
If this does not fix the problem then send it out for repair to a reputable and experienced shop.
Ciao,
Adrian.

Lorenfb

The problem you describe is the most common one for a 964/993 CCU.
When this failure mode occurs, the CCU fails to shutdown with the ignition switch.
For the most part, though, these units are very reliable.