what causes a/c heater blower motor to quit blowing under engine "load"?

blower works on all speed settings, for both heat & A/C, but under acceleration or particular strain/load on motor, it will quit blowing. let off the gas a little bit, and it will start blowing again. very strange. was also battling a wet passenger side floorboard, thought a clogged condensate line might be culprit for both issues, but not the case...  anybody else experience this?