If PB3 fails to close when pressed, what is the consequence?

In the context of a programmable controller system, when a push button such as PB3 fails to close, it typically indicates that the signal to move the door up does not get sent. If PB3 is specifically designed to command the door to move up, its failure implies that the upward motion cannot be initiated. The other operational state—moving down—would still be possible if another control (for instance, a second button) is functional. Thus, the consequence of PB3 not closing would result in the door being unable to move upward while still retaining the ability to move downward through another switch or mechanism. This clarification of functionality is essential in systems where multiple control inputs affect the operation of a single output device, like the door in this scenario.