Inoperable radiator fan

Single radiator cooling fan does not operate; no longer cycles on/off while driving or idle;
fan only operates on low speed when air conditioner in on. No fuses blown; installed new fan relays #1 and #2;
installed new coolant temperature sensor, all to no avail. What's left to replace
other than the fan resister and engine control module?
is there another relay or module controlling the fan?
vehicle has 63,000 is lightly driven, usually sits for months, used as second vehicle.
ran errands few days ago, fan never came on, no temperature indicator illuminated
on dash while driving, vehicle did not overheat. Otherwise,
vehicle is in excellent condition.