Mark

Let's look at the pressurization problem....

Manual mode is 28VDC powered and operated completely by the overhead control panel. It uses a DC motor on the outflow valve.
This "is not" a preferred mode of operation as it takes considerable effort to maintain proper pressurization through all phases of flight.

In Auto mode, the system is controlled by the Pressurization Transducer. It is a AC system. Inputs are (either) ADC, Air/Ground, and the Landing/Cabin Alt Selection Panel (on right side panel). The outflow valve motor is AC powered.

What exactly is the crew saying as far as the fault goes?

Has power been checked? Any fault lights on transducer? Has the alternate Air Data been tried? Is the outflow valve reacting when simulating air mode? So many more questions.....