Defroster Not Working IN Florida (91 US Testarossa )

Dear Ferraristi,

I Know, I know, don't laugh. My defroster isn't working and I live in central Florida. I'm just the kind of guy that if I find something not working, I just want to fix it. Anyway, the fuse checks out, all the relays are new ( changed to updated plastic housing relays to eliminate heat ( old tread on subject)) Those upper console switches are sort of flakey. I have changed out my foglight switch at least a couple of times. What wires do I jump to imitate an "on " condition on the defroster to see if it is the switch.

Any help is always appreciated.

Shamile

Freeze, Miami Vice

91 US Testarossa

 

Shamilie -- Do you mean the electric defroster inside the rear window?

 

Shamile - If you are referring to the front dash/windshield defroster, then -

check the vacuum hose where it attaches to the vacuum canister/reservoir. This plastic canister is located in the engine bay above the driver-side rear wheel. The hose is a small diameter (5 mm - I.D.) black flexible tube that runs from this canister to the under-dash ventilation system. The canister is connected to the intake manifold which generates the relative vacuum.

The hose becomes brittle with age and heat, and ultimately looses its seal. Vacuum valves and actuators control the defroster, as well as all of the other vent functions in the Testarossa.

My defroster failed to work one day, and after some investigation I found that this vacuum tube had come off the canister. Upon cutting 2 cm off to gain fresh rubber, I reinserted it onto the canister nipple and everything worked fine.

Good luck.

Jim S.

 

Dear Ferraristi,

Oh sorry, I forgot there are two defrosters. What do I know, I live in FL & GA. Anyway, I am refering to the heated element in the rear window. When I push the switch nothing happens. I don't get a click or a light on the dash. Can I bypass the switch to imitate an "on" position?

Please let me know.

Shamile

Freeze.....Miami Vice !

 

OK -- for the wires at the rear window defroster switch:

RN (red/black) = +12V power (always) from fuse #2 to run the heating element (when the switch is closed)
BN (white/black) = ground for actuating the switch's internal closing mechanism and for the instrument light inside
VB (green/blue) = +12V power (when key "on") from relay S and fuse #22 to run the switch's internal closing mechanism
L (blue) = wire going to the "+" side of the heating element (the "-" side of the heating element is always at ground)
G (yellow) = +12V power for the instrument light inside (that comes on with the other dash lights)

If you unplug the switch and manually connect the RN wire to the L wire in the harness connector with a jumper, this simulates the "closed" switch -- i.e., the heater element and the rear defroster indicator light in the main instrument cluster should be "on".

If you've got +12V on the VB wire with the key "on" (and the BN wire is at ground), but the switch (when plugged in) doesn't connect the RN wire to the L wire when pushed, the switch is probably toast.

If you don't have +12V on the VB wire with the key "on", you'd be checking relay S, fuse #22, and the interconnections (but so many other important things rely on relay S and fuse #22 working, that if no +12V on the VB wire is your problem, it would almost have to be something in the connections from fuse #22 to the switch).

HTH -- let us know what you find.

 

Dear Ferraristi,

Once again Steve has come to the rescue. I followed Steve's detailed instructions for troubleshooting the rear window defroster. It turns out to be the switch. I can manually turn it on by bypassing the switch as Steve describes. One thing though, my " VB " wire is a green - white not a green - blue. Is this different on a 91?

These switches are such a pain. Stupid overcomplicated double relay switch. I have already replaced them a couple of times already. This time Ferrari wants 212.00 for the defroster switch. This is so crazy. I remember my 20 + 308 never had a switch problem. I miss those nice solid "click" switches.

Anyway, thanks again to Steve (91TR ) who never fails to come through.

Shamile

Freeze....Miami Vice !

 

That's just my mistake by typing faster than the brain was working (B= blanco = white, not blue).

Glad you at least know where the problem lies, even if it's painful (which it usually is )

 

I am checking on my car defrost switch, the problem is I don't know if it's on or off, is there any indicator on the dash shows if it's on ? The switch itself has no indicatior too. Thanks