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911 3.2 Carrera (1987)

C

cje

PCGB Member
Member
Hi, Fresh air fan and footwell fans not operating after 3/4months of no use of car. Heater fan in engine bay & heater control lamp working OK. I’m guessing it is an electrical problem. Are the footwell fans and the main fresh air fan connected electrically. Fuse is OK. F relay swapped for another and no change. No burning smells. All equipment behind the shroud protecting bulkhead fans looks like it all came out of Stuttgart yesterday!! Any advice/ ideas Please. I have a Bentley service manual.
CJE

 
If no burning smell then the fresh air fan hasn't seized. So even though the fuse appears good try cleaning contacts of fuse carrier, which can often corrode and prevent good electrical connection (from experience!).
 
Geoff997 said:
If no burning smell then the fresh air fan hasn't seized. So even though the fuse appears good try cleaning contacts of fuse carrier, which can often corrode and prevent good electrical connection (from experience!).
Click to expand...
Hi Geoff997,
Thanks for your reply. Cigarette lighter off the same 5amp fuse works, but cleaned it anyway. No joy with fresh air fans. Heater fan in engine compartment and it’s controller work just fine And with heater control turned off there is a zephyr of cold air to the screen and through the dash vents and footwell outlets notwithstanding the fans are not working.
CJE
 
Footwell blowers have fuses attached too, at least I think the later ones do.

Were the FWB working before? Pretty sure they are on a different circuit to the fresh air fan - most likely the fresh air fan motor, common issue
 
Fresh air blower switch is 2 pole 3 position. 1 pole switches fan speeds and the other just illuminates a lamp. Both from same supply, so does the lamp come on?
If yes fault is with switch or fan assembly
If no then there is a power supply issue
 
Geoff997 said:
Fresh air blower switch is 2 pole 3 position. 1 pole switches fan speeds and the other just illuminates a lamp. Both from same supply, so does the lamp come on?
If yes fault is with switch or fan assembly
If no then there is a power supply issue
Click to expand...
The fan lamp symbol illuminates. I removed the radio in hope of checking the switch but access looks impossible. Can the switch be removed from the dash in any way To check for wear. Seems unlikely that all 3 positions are worn?



 
Hi Cornershop thanks for reply. FWBs were working OK before. I will do some more checking re fuses.
 
Hi T911UK.
Thanks for your reply. I will check main fan by running 12volt through it.

 
Hi ALL,
Thanks for your help. Removed main fresh air fan. 12 volt feed no result. Checked carbon brushes. Live feed brush holder melted. Brush worn out. Now sourcing a new main fan!!
Best Regards
Clive


 
Hi Thanks to All,
new electric motor fitted to existing fan. Success! BUT lever controls are as follows - (1) full speed (2) slow/med. (3) full speed. SO.....does that mean the resistor needs replacing to obtain- slow/medium/ fast ?
I just love my 3.2 as a hobby!!

Clive
 
Hi Clive

The medium and fast speed resistors each have a bimetallic contact in parallel with them (I'm learning most of an SC 3.0 is controlled by bimetallic strips ;-))

If the resistors overheat the bimetallic strip flicks over to short the resistor - so will then run the motor full speed - but allow the resistor to cool.
I found my strips were bowed due to rust buildup? I decided to slightly bend the bimetallic contact away slightly until the contacts were just open.
I worked on the theory rust would only coke back but hopefully the bimetallic would still operate and close if the resistors overheated.

I left running on a bench for ages and had no disernable heat coming off the resistors anyway

Don't know how others feel about doing this?

Regards
Neil

 
Sorry, I meant the slow and medium speeds have the bimetallic strips.

Also, clean the contacts as a precaution after bending - to ensure a short circuit in the instance the strip does "trip" through the resistor overheating
 
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