Now it gets a bit hazy with my notes, but I would go so far as to say that the EIU's signal the APUC via the ARINC bus to say that the door is fully open due no timer operation. Or timer has exceeded 60secs and no start and APU DOOR status.
I'm afraid we'll have to agree to disagree on this one.
My notes say:
"Should the door fail to open to position greater than 13 degrees, the electrical circuitry of the APUC prevents the APU from starting...."
13 degrees is enough to start the APU, but it's just not advisable to run the APU on the ground for long periods like this, hence the EICAS message if the door doesn't reach the fully open position. I believe the APU Maintenance Page uses the 13 degree switch to show OPEN, rather than having a circuitous path from the actuator to the EIUs to the APUC.
I wanted to prove this for myself a few years ago, but never got the opportunity to have an observer in near the door and in the cockpit communicating to each other. It's too difficult to see when the door stops moving from the ground... and I'm not going to suggest to a currently serving engineer to pull the EIUs and start the APU just to prove a point :P
My Engineering training notes also say (regarding the APU Maintenance Page):
"I
nlet Door Position... The APUC senses door position from the 13 degree inlet door position switch"
also..
"
Starter Status
- The APUC commands the starter on and off. The starter engages after the APU selector switch is rotated to start and the APU door opens greater than 13 degrees"
Cheers
NSEU