The PV-T-AD1 and PV-T-AD4 are pressure transmitters that are installed on CROFCUs, these devices measure the difference in pressures in filters. If either the fan or filter are too dirty this device will alarm you. The pressure setpoint are usually set, and if it goes out of range, this device would alarm the BAS when a filter has to be changed.
Manuals
CROFCU Pressure Transmitter Manual
Tips and Tricks from the Daldrop Team
The way we start up these devices are by testing if the device is working correctly at both sides. With a meter you can measure the voltage coming into the PLC. You can blow into either side and you will see this voltage rise or decline.