Dodge: blower problem -- 1989 colt

hi,
x-posted
1989 mitsubishi / dodge / plymouth / chrysler 1.5 l engine, 4-cyl colt
AT; fuel injected... (alternator replaced in 2000)
problem: when the blower has been turned on (either air or heat) the
engine DECREASES power (significantly) and gets very rough (especially
in reverse) even if the blower is turned completely off...
the only way around this is to restart the car (shut it off and back on)

question: although (i think) the blower needs to be replaced why does
the car continue to run as if it is on (very rough); no power.
thank you in advance
(p.s. before this (above) started to occur, any accessory would cause
decreased rpms however when turned back off the auto would improve.)