Final answer:
The problem, indicated by gauges rising to zero psig during evacuation of an AC system, suggests an external leak. This happens because the pressure should not rise if the system is being evacuated properly. A gauge reading of zero actually reflects atmospheric pressure due to a breach in the system, not a fully evacuated state.
Step-by-step explanation:
If you observe the gauges on an AC system rise quickly and continue to rise until they read zero psig (zero kPa) during evacuation, it indicates an external leak. When the system is evacuated, the pressure inside should drop as air and refrigerant are removed. If the gauges instead show a rising pressure that goes to zero, this means atmospheric pressure is entering the system, which occurs only if there is a breach allowing outside air to enter. Pressure gauges are typically calibrated to read zero at atmospheric pressure; thus, if the gauge reads zero, it's actually indicating atmospheric pressure rather than a complete vacuum.
An external leak can compromise the evacuation process, leading to improper AC function, and must be identified and repaired before proceeding with AC system service. None of the other options provided (excessive moisture, restricted expansion valve, or restricted evaporator) would cause the described issue during evacuation.