Your Generac 7.5kW diesel generator likely has a damaged starter solenoid or starter motor from extended cranking with a weak battery. Check connections, test the solenoid, and inspect the starter before seeking professional repair.
Keep your RV generator running reliably with this comprehensive maintenance and troubleshooting guide for Onan, Generac, and Cummins units.
Consistent 2-minute shutdown under load indicates fuel delivery cannot keep up with demand. Check fuel pump, bleed system, verify no restrictions. Also check if generator is undersized for AC load - may need soft start on AC unit.