Voltage check your fuses with ign on engine running or not, and find one that the steel clips have corroded a little/lot? and allow the fuse to run hot, melting the internal solder connection holding the element/fuse wire/conductor to the little silver end caps....
now this heat can also be caused by the crimps on the steel clips that go to the copper buss bars in back, they can also corrode and heat up, sometimes even melting the black housing ......
BTDT in several cars.....just replaced one for that exact reason in my '72, it was the a/c power no a/c at all, not even a blower, it's the lo power section of the control pack, :shocking: