* Blower Motor Resistor: This is the most common culprit. The resistor controls the different fan speeds. When it fails, the motor might run at only one speed (usually high) or not at all. The jump start likely provided enough power to overcome the failing resistor temporarily. It's now completely failed again.
* Blower Motor itself: The motor might be failing internally. Worn brushes, a failing winding, or seized bearings can cause intermittent or complete failure. Jumping it temporarily provides enough extra power to overcome some internal resistance, only for the problem to return.
* Wiring/Connectors: A corroded, loose, or broken wire within the blower motor circuit can cause intermittent operation. The jump start might have temporarily improved the connection, but the underlying problem remains.
* Fuse or Circuit Breaker: Although less likely given the previous success, a failing fuse or circuit breaker could be intermittently cutting power to the blower motor. It's worth checking these.
* Switch: The blower motor switch itself could be faulty. A worn or damaged switch might only provide intermittent contact.
In short: The temporary fix masked the real problem. You'll need to diagnose the actual cause rather than resorting to more jump starts. Start by checking the blower motor resistor (this is often the cheapest and easiest fix). If that's not it, you'll likely need a multimeter to check for power at the motor and along the wiring harness to pinpoint the fault. Professional diagnosis might be necessary if you're not comfortable with electrical work.
