Why could my heater resister in my car keep blowing out?

Hello,
I have a 1998 dodge stratus 2.4 engine, and 2 weeks ago the blower motor resister went out, so I replaced it. Then 6 day later it blew again, hoping it was just a dud, I went out and got another one. Ten days later it went out again (yesterday evening). I had my blower motor tested before the 2nd one went out about a week ago, and it tested at 12 something.. I can’t quite remember what, but my mechanic said it was a little low for my blower motor but it was within range and it “should” be fine. I’m now stuck wondering what to do? The blower motor in my car isn’t the easiest one to replace, and I’m not even sure that’s where the problem lies. If it is not the blower motor any other ideas on why my car keeps blowing my heater resisters? Any help would be greatly appreciated! Thanks!