Disconnect the vacuum switch from the I/O PCB. Put a jumper on the vacuum switch connector pins on the I/O PCB. The connector is at P23 for CHC  and P34 for NGC .
Go to Enclosure Exhaust Clogged on the I/O tab of the Diagnostics screen. Verify the value changes state when you put the jumper on the pins. If the value changes state, replace the vacuum switch.
If the value does not change, check the cable for damage. If the cable is not damaged, go to I/O PCB - Troubleshooting Guide (Classic Haas Control).