Four-min drain periods came into play on 18lb super-capacity models, as stated above. Standard-capacity models were always 2-mins, as I recall, including when both sizes were in the line.
The longer time, of course, was to insure full drain of the larger volume of water involved in a full load across a variety of conditions that could potentially affect the flow rate, such as drain hose restriction, a high standpipe, clogging of the self-cleaning filter accumulated over a period of years. Possibly also to allow for some "drip time" to lessen the volume of water the pump had to handle at the start of spin of the larger loads of highly-absorbant items such as towels.
Our 1976 18-pounder drained a full load in just-about-right-at two minutes for several years then got a tad slower as it aged.
The spin shift solenoid circuit passes through the water level switch, and it won't engage unless the pressure switch contacts are reset to "empty tub" state. Attempting to spin with water in the tub will give a neutral drain until the level drops to the reset-point, then it will typically drop out of spin when the water swirls up enough to trigger the switch again ... possibly shift in-out of spin a couple/few times until enough water is drained so the switch no longer triggers on the swirl-up. The only way to force a spin-drain on a belt-drive is to manually reset the pressure switch by holding it at Reset position if a variable type or between positions for switches of the fixed-level(s) type.
