the 24vac transformer in my inside unit of A/C system was burned out 3 times in this winter. one month ago, the unit did not work, no heating, no blowing. we found out the transformer burned out and replaced it. one week ago, burned out and replaced it again. yesterday (worked for 5 days) it was burned out again. there is no fuse on the inside unit board. this is a electric heating system. any suggestion to figure out this issue is appreciated. thanks.