The old Electrolux fan motors don't have resistors. They are a multi-winding motor. The resistor set-up was introduced later with the 240s (circa 1980 or so) when Mother Volvo went to a cheaper fan motor.
Intermittent cut-outs are a sign that the brushes may be failing, and/or the bearings may require lubrication with a little bit of graphite.
Here's a pic of an Electrolux fan motor with my test rig.
Here's a close-up of the area where the brushes sit.