Heater fan motor has some type of electrical problem. Acting like an electrical short… and cycles up and down and off and on … problem started today.
Fan motor and resistor were recently replaced . Have had no issues till now
You probably need this.
Because of this.
Tester
A shop would probably start by using their DVM to measure the voltage at the blower motor for the various switch positions. If you know how to do that, report back what you measure. For most car owners though about all you can do is read what the owner’s manual has to say about it, and check the fuse for that circuit, and if that doesn’t do the trick, schedule an appointment at the shop. The above post about the TIPM is a very good guess where the problem is located.