My AC fan ( C230 1997 ) does not always come on in any function mode....auto/manual high/low fan. Then out of the blue it starts up...this often but not always after going over a bump in the road. Then other times the fan rpm lowers when I accelerate and increases when I let up on the gas. Is this a vacuum or an electrical problem? Or both??

 

feel if the blower fan is hard or binding. try turning it by hand.

if it's good, then the regulator could be faulty. measure the voltage coming out from the regulator at different blower speed.