When should which fans run?
The only fan that runs while using Microwave (only) mode is the electronics compartment cooling fan. I'm pretty sure that when new (unit ~ 2 yrs. old), the convection fan motor also ran, circulating air within the cooking chamber even during microwaving (only) use. The convection oven fan runs when in Convection (only) mode. The oven (chamber) light operates normally, the unit heats well in Microwave (only) mode, but when new a fan ran, quite audibly (which fan? No idea! However, NOT the cook top over-temp fan, which I believe is also the Vent fan.) that is not now running, or else the electronics cooling fan got unusually quiet for no reason. The cook top Vent fan seems to run normally, switch controllable.
Stirrer motor/ turntable motor/ damper motor all seem to operate normally.
The troubleshooting guide that's part of the wiring diagram (P.N. 3840W1T150E) included with the machine is insufficient for the purpose of determining the sequence of events for the various operating modes. (The wiring diagram itself is wrong also, but that's another question...)