I appreciate all the help and guidance. These recent answers have been
clear and easy to understand. Hopefully this is my last question on small
motors for a while (if not, I'll need more humor, but am willing to learn).

Can anyone educate me on "Thermal Protection" Rating on electric motors.
Old motor is "AA", second motor canabalized from a friend's old spa is C1
(works well on low speed, but overheats in 30 minutes to an hour on high
speed),
Store recommended and purchased motor is "MA" and overheats even on low
speed -- not good.

Tony & Ron, you got me to understand Insulation Class, Thanks, If someone
can educate me on "thermal protection" ratings or point me in the right
direction to look, I should hopefully know enough to take the new motor back
(it appears undamaged, just gets warm after use and shuts itself off,
electrical connections and windings look clean and new) and exchange for the
correct motor. The salesman seemed clueless on these ratings and he is the
"technical guy" for the store. By process of elimination, I'm guessing the
ratings have something to do with why the motors are over-heating. I can't
find an electric motor repair place in my area to take the motor in to so I
am at the mercy of the spa store. I'd at least like to be knowledgable so I
get the right motor.

The cord and control box are the other common links in the problem. When I
moved the cord from the original motor to the others I examined it --
Condition look's good. Opened control box, some minor corrosion, from damp
air over time but not sure what to check in here. Nothing looks badly
damaged, overheated or burned. I did remove a moderate sized cobweb
attached to one electrical component. If the next motor has problems I will
have to suspect the control box. It seems easiest to try to get a new motor
that matches the old on thermal protection (already matched all the other
specs except minor difference on amps and 3.1 vs 3.5 as I understand it
shouldn't matter, just means newer motor is more efficient, correct me if
I'm wrong), but "has the rating terminology for thermal protection changed
over the last ten to fifteen years" (best guess at age of original motor
based on info on plate, hard to read). If someone can educate me I'll at
least know what to look for in the way of thermal protection.

All the motors meet the specs you all explained for Insulation Class, and
ambient temperature for where used (and match to the old motor). Thermal
protection code on each is different.

Thanks in advance,
Andy