Ferrari Mailing List: Testing transistors

[Peter Rychel (dino308gt4]

This is a Ferrari topic because it’s for my Mondial.

 

The only thing that doesn’t work for the HVAC system is the fan speed switch. It’s either completely off, or, full blast.

 

Checking the archives at F’Chat there could be two, possibly three things at fault; either the switch itself, the power transistor for the fan motor, or, the A/C system control ECU. I started with the switch because it’s installed on the center console and I had issues with the fog/parking lights switches located next to it before.

 

I took it apart and have checked to the best of my ability all of the components with my voltmeter (simple continuity checks). The pots show progressive resistance values through their sweep, as well as the resistors, caps and diode. There is a Darlington transistor located directly below the pots which have failed in other cars. From what I can see, it’s a BD238.

 

Other than measuring resistance between the collector, base and emitter terminals, is there another check I can do without removing it from the board?

 

Another component that fails is the power transistor located on a heat-sink in the main duct work of the A/C unit in the dash. This is the actual component that regulates the fan speed (supposedly a TO-3 type #2N3055). I haven’t removed it yet but at least the leads can be unplugged and I can do a continuity check on the terminals (as well any other diagnostic test I can do).

 

Thanks guys!

 

 

 

 

 

Peter

 

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