Notes on Testarossa A/C Blower Motor Troubleshooting

Hello gents.
I hope you don't mind if I bother you with a few notes of my recent troubleshooting exercise for an inoperative A/C blower motor on my 1989 Testarossa. Many thanks to Steve Magnusson , who provided valuable feedback during the process.

The blower motor worked well when I bought the car, but only when max fan speed was selected on the control dial. I suspected my car suffered from the typical fan speed transistor failure but I wasn't too concerned about that, initially. Then one day my blower fan stopped completely, and would blow the 20-amp A/C fuse, immediately, whenever I selected max fan speed. I thought the transistor may be part of the problem so I replaced it with a brand new item from Ricambi.

https://www.ricambiamerica.com/127014-power-transistor.html

Same thing. No fan operation and the 20-amp fuse would blow as soon as I selected full fan speed. I suspected the blower fan motor may be seized so I started to investigate.

The blower motor resides inside of the HVAC unit under the dash and cannot be easily accessed. But the power leads emerge from the HVAC unit and can be accessed by removing the two screws from the top edge of the fuse panel, laying the fuse panel forward and down, and then removing the left-most (from the driver's viewpoint) of the three vertically-mounted relays. The blower motor leads (black, brown on my car) terminate in a black connector that connects to a wiring lead (brown, green + red) that feeds into the vehicle wiring harness. Per Steve M, this connector is not depicted on any of the Testarossa wiring diagrams. But it's in there, in my car at least. Undoing the black connector gave me direct access to the A/C blower motor electrical power circuit.

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I fabricated a jumper for the blower motor wires, then used a strong 12v power supply from my RC car starter box to feed 12v directly to the blower motor...bypassing any of the A/C control circuitry of the car, to see if the fan would operate or not. In this configuration the fan motor should have run at full speed, but it only groaned and turned maybe 10 rpm. I suspected the motor had failed, possibly the bearings.

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(see attached video)

Just to make sure the fan was not restricted by any sort of debris, I used my flexible boroscope camera...

https://www.amazon.com/dp/B0B8HKQFPD?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1

...to take a good look at the plastic squirrel-cage fans that are mounted on either end of the blower motor. I got a good look at both fan elements, and they were clean and showed no abnormal signs.

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I purchased a new VDO BM381 blower motor from eBay for $50...

https://www.ebay.com/itm/156960719192

...and wired it into the black connector that feeds into the wiring harness. With my daughter's help, I operated the A/C controls from the cabin, while observing the operation of the new blower motor. Sure enough, the new motor spins free and strong, and the speed is variable by using the fan speed select knob (but the operating RPM range seems pretty small). The 20-amp fuse did not blow during the process.

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So there you have it, verification that my A/C blower is bad and will need to be changed. You guys know what is next.....a BIG job! I'll keep good notes, take lots of pictures, and will let you know how it goes. Stay tuned!