I had that same issue. It turned out my circuit breaker was the incorrect amperage and was tripping every few minutes. It was also getting very hot! I installed the correct amperage breaker and also switched both relays to the McKeen solid state. Those two actions alone reduced heat drastically and stopped the breaker from tripping.
While you’re at it, check the blower resistor pack near the blower motor. Mine was extraordinarily rusty. IIRC it only controls speeds 1 and 2 but it’s a cheap and easy replacement if needed.