It dose make sens. Tripac APU have a in line 12 v primer pump , something that I don t see on carrier. No wonder why they updated with 12 v in line electric pump. Myself I had same issue. First it got fixed by replaissing in line small fuel filter ..them it start shutting down after 2 days working and last time after about 5 min working. I replaced the big fuel filter (full with diesel) and the primer fuel pump ..and still just cranking. I made sure to crank and release the air also from the screw and the metal lines to. They (online) selling 12 v in line pump on Amazon and e Bay (can try same as for tripac apu), I'll try and see if it brings back the pressure needed for smoth run instead blowing air in the tank.
How I primed my carrierpro apu, I had to relocate my unit from the frame side to the catwalk, as in behind the sleeper between the framerails. When I disconnected my fuel lines it lost prime. After relocating it and reconnecting all the wiring and fuel lines it would not start. Tried starting through 9 cycles. Nothing.
I got out my weed spray bottle with a hand pump, put fuel in it, Hooked it to my fuel supply line and opened the air bleed bolt on the apu then pumped fuel into the system, closed the bleeder, reconnected the supply line to the fuel tank. The motor started on first cycle, sputtered a bit
And then ran fine.