blowing fuses

[marlborolights]

good day,

i recently picked up a winter beater, a 1990 olds 88. my heating was only working intermitantly, someone had told me to just tap the motor, to get it going when all else failed. that only worked for a while... just recently i changed the heater motor, it was working great for a couple of days but now it just keeps blowing fuses... the fuse that keeps getting blown is 20amps. does anyone know what could be the problem and possible fix? is it ok to use a 25 or 30 amp fuse???

thx, in advance!