and like said above .... the case might just shock the hell outta you
Yup, any time I see an iced evaporator, first thing I do is mark the clock. Then continue with preliminary inspection and gathering model/serial info.
I've definitely seen dtfd's cause the defrost timer issue as previously described. It terminates the instant it starts, so to speak.
But, for what it's worth, I've seen fan behavior just like this which was caused by residual ice in the core of the evaporator, which blocked air flow through the coil and so the only other place for the air to travel through was through the "weaker" fan, fighting against it. (Note that weaker doesn't necessarily mean a defective fan, but in this scenario, one of them will dominate the other.) Pull the blade assembly off of the slower fan and see if the motor comes up to speed. And get a -bright- lite and make sure that coil is clear all the way through.