Generally if the module is a resistor, there is one position where the motor is fed directly. So when the resistor goes open, your only speed is full blast or off.
If you have more speed values than could be explained by taps in a resistor, then you have an electronic control of some flavor. Usually when the electronic control fails, you have no fan at all.
I've replaced these in VWs, Mercedes, and Infiniti. The reality is the expensive cars have just as shitty fan controls as the cheap cars.
Exar has/had a group that did nothing but reverse engineer the electronic modules for replacement parts suppliers. You can't believe the crappy designs used by the manufacturers. It was always a problem if the replacement parts some use good engineering, or just copy the moronic designs of the OEM.
I used to think they potted all these modules to protect the circuitry from the elements, but in reality they were just kind of embarrassed at the poor engineering in the design.
Most of the time the bipolar designers would spot circuitry that had potential to damage on start up. As you probably know, breakdown voltages in bipolar can be a function of pins being floated or shorted to other pins.
Resistors or electronic controls need heat sinks, so I don't think you can tell based on the outside of the package.
The replacement part for my Infiniti blower control was a Delphi make in Mexico! The original part, which looked a bit different (bigger heat sink) was made in the USA. The Infiniti part isn't potted. I saved it just to open it up and see if anything smoked. It looks clean. It is a PCB with 4 semiconductors, one power device, and what looks like a surge suppressor. The PCB has Picotech on it. It has a 0.004ohm current sense resistor on. I suppose I can salvage it for yucks. The board is conformal coated, which makes it hard to read chip numbers.
If I had to fault them on anything, I would say too much heat sink grease. It is oozed all around the power device. [3 pins, so MOS or BJT].