2001 Chrysler Voyger minivan Blower Motor Resistor Keeps Burning Up

I have a 2001 Chrysler Voyger Minivan that keeps burning up blower motor resistors. Six months ago the AC blower motor would only work on high speed so I took it to my mechanic and for $170.00 he replaced the blower motor resistor, so when it started doing again last week I decided to buy a resistor and replace it myself. I bought one at a local parts store for $13.90 and installed it in five minutes. The blower motor worked fine on all speeds for 3 days with a puff of smoke coming out of the AC vent it was gone again. I bought another resistor at the same store with the same results, all speeds worked for 2 days and then the latest one smoked. Now I'm back to square one, with just the high speed working. I just spent $1200.00 with my mechanic 3 weeks ago on various repairs. Can anyone offer any advise on what the problem is so maybe I can repair it myself. I can't afford any more auto repair bills. My sons car just cost me $3000.00 last month in repairs. This is my first post so I hope I can get help. Not sure what I'm doing or how to get answers.

is it oem resistors?, I would have your mechanic check amperage draw at the blower, also check voltage drop on the ground side of the blower motor