Blower motor won’t turn on with AC in my ‘73

[snowball]

Check the fan. see if you're getting 12V with the switch on. IF not check the switch. make sure you're getting 12V at the switch and each of the settings out to the fan resistor.

It's great that it's an all original 55K mile truck but you need to realize you have a 40 yearl od truck with 40 year old problems. Sun, heat, cold, All cause problems. Had a friend and he couldn't understand why he neede to replace all vacuum and eater hoses on 40K mile car. It was 20 years old. dry rot is a B.