You'll need a workshop manual with wiring diagram to diagnose efficiently. With "most" a/c fans, they are usually permanent magnet motors, to test them, unplug them, power the 2 wires with 12 volts, when connected they should spin rapidly and produce lots of air, when hooked up backwards (positive/negative reversed), they'll spin faster, but produce less air, less load due to the design of the cage of the centrifugal fan.
Generally a/c fans are speed controlled by inserting some resistance into the circuit to limit the current, these open resistors require cooling and are normally located in the air duct to keep them cool.
Late models may be electronically controlled, I am unaware of what actual configuration is in your machine.
If your motors test correctly at 12 volts and are slow or don't work when hooked up, you'll need to do some additional testing.
