This all gets me confused... I tought it is impossible to run the APU without left ac or dc pumps! Now what Lightning 5 tells is definitely not true, the left AC boost pump WILL operate even with the switch in off.
With the airplane on the ground and the APU control selector ON the L FWD boost pump starts. If the boost pump generates sufficient pressure, the DC fuel pump remains off. The L FWD boost pump remains on regardless of its switch position as long as there is 115 vac power, the APU control selector is ON, and the boost pump is not faulty. Pulling the 115 vac circuit breaker for the L FWD boost pump shuts the pump off and starts the DC pump in the left fuel system.
Now, since the APU controller gets a pump pressure signal from the left AC and DC pump, it will never open the APU shutoff valve when both pumps stay off (and you'll get a message DC Pump).
With refuelling door open, you can get the center pumps to run indeed, but the APU will still not run I believe...
This is also what I read in AMM, so can anyone confirm that the AMM could be wrong here?