These aux fans were designed to cool the condenser under high a/c loads and not necessary to cool the engine. If your engine is running hot it's almost invariably a bad/clogged radiator or somesuch...kludging the a/c aux fan is not a good thing to do although it seems to be real popular.

Further, a powered rotating fan presents an airflow BLOCK at road speeds probably above 30mph where you get more than enough air through the radiator by car motion. One of the advantages of a thermostatic clutched engine driven fan is that it doesn't power the fan when the radiator is sufficiently cooled by air drive/sucked through the fan by the vehicle forward motion.

Lastly, it's just another electric load on a generally undersized electrical system....and when you need the aux fan it might be worn out.