Testarossa Climate blower motor problem .

Did this happen when:

1) the STOP pushbutton was pressed (the blower motor should not even be trying to run) or

2) with one of the other pushbuttons pressed (the blower motor would be trying to run)?

There is a power transistor associated with the blower motor that is mounted in the TR center vent area. If you got the smoke in condition #1, I'd inspected the power transistor. If you got the smoke in condition #2 = could be either the power transistor or the blower motor. Here a pic showing the rivets that hold the power transistor assembly:

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And this is the 127014 Power Transistor Assembly that is riveted in the center vent area:
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If it needs a new fan motor I found VDO PM381 fits.

 

Certainly try replacing the power transistor first to see if the blower motor then works. The tricky bit is the mounting of the transistor to the heat sink. The outer case is an active wire (one of the wires might be connected to other end of that screw with the arcing) so can't be electrically connected to anything else -- there should be electrical insulators. Try a search on "TR power transistor" or "2N5886" for prior threads -- IIRC, that stock 2N5886 is rated at 25A, but people have identified other TO-3 transistor(s) that have a higher current ratings.

Shame that they mangled your housing of the AC unit so badly -- just drilling the rivets out is all that was necessary.

 

Yes, you can replace just the transistor itself and reuse the heatsink (but make sure the mounting hardware was not messed up from the prior replacement).

 

Sure.

 

When you diagnose it and take it apart far enough to know what you need all your questions will be answered.

 

The 2 shaft blower motor? In other auto A/C units, the speed is controlled with simple resistor switch. Why did Ferrari use a transistor ?

 

For the same reason since the close of the Victorian age most manufacturers have used PWM controllers.
Its simpler, cheaper, it causes less fires and it uses much less energy. You also have infinite fan speed control instead of preset speeds.

I told the guy at Rolls Royce school after spending an hour on the massive diagram for their 16 speed fan speed control system using an entire bank of resistors and another bank of relays in various combinations "Why not just use a PWM controller?". I thought his head would explode. They had an entire giant wiring diagram page, about 20 lbs of components dedicated to their fan speed control. It all sat in an insulated space under the hood it generated so much heat.

 

This is not uncommon. It allows the use of two smaller impellers on each end that are more similar in diameter to the motor = it packages smaller/better than a single, larger diameter impeller while giving the same airflow.

Because the TR wasn't designed in 1950? Seriously, the (common emitter) transistor arrangement has some advantages:
1. Provides continuously variable motor speed control.
2. The resistor arrangement dissipates more heat and uses more electrical power. (The transistor also runs kind of "hot" so that's why it's mounted in the output airstream of HVAC unit, but it uses/wastes less power overall.)
3. The resistor arrangement requires more large gauge (heavy) wiring and a more expensive high-current capable multi-pole switch.

I will give Ferrari a bit of a negative mark for not communicating to the HVAC vendor that the transistor needed to be easily accessible and replaceable. It's not super-difficult to do once you know how/where it's mounted, but Jose's photo shows that it's not obvious how to do it correctly.

 

You can relocate the transistor to a new location, but then it's up to you to ensure that it has enough total cooling (i.e., heat sink + airflow). The transistor is mounted in the center vent to always give it some airflow when the fan motor is operating (but it isn't much of a stock heatsink). I have no experience relocating the transistor nor using a different heatsink, but, if it does fail again, maybe it will be easier to replace in a new location. My "solution" was to only operate the fan speed at maximum (which uses a relay to supply the motor current and not the transistor) or at 1/2 speed or below. Operating the fan at 3/4 or 7/8 speed cooks the snot out of the transistor.

 

I bought the biggest heat sink I could and mounted it under the passenger side crash bar. It is easy to service and doesn't run burning hot. I'll find a link to the one I bought.

 

https://www.ferrarichat.com/forum/threads/power-transistor-2n5886-heat-sink.657938/

Please see post #10

 

the problem with the Ferrari solution is that the heat sinking is practically non existent with the way it is mounted. blowing air on the transistor itself is not good enough. to further exasperate the problem, you need more sinking the lower the fan speed is.
there is reason why audio/signal power amplifiers sit on fined heat sinks. heat needs to be first drawn away from the transistor to a smaller surface area (fins) where air can then draw away the heat from it.
the solution is really to remote mount the transistor on a proper large enough heat sink..if mounted correctly, convection is enough.

 

I just did it by manually operating the speed control knob in that fashion (after I had replaced my bad transistor with a new one).

 

But even in Texas I only use about 25% fan speed. I get too cold otherwise.

 

Post 2 is the heat sink and fans I used.
Mounted on back side of footwell panel.