Check the listing for details. Tjernlund MODEL PS1503P Duct Airstat Switch (Plug-in). Condition: New. Listed at 85.00 USD. The PS1503P Duct Airstat switch is designed to sense the positive pressure increase in a supply plenum or duct when an air handler or furnace blower is in operation. The increased duct pressure expands a diaphragm which in turn mechanically closes the normally open electrical switch contacts to activate accessories in tandem with the central blower. Typical accessory devices activated include duct booster fans, UV air purification units and furnace mounted humidifiers. Electrical Ratings:7.0 Amps Non-Inductive (Air Purifier)2.5 Amps Inductive (Duct Booster, Humidifier) Electrical Switch: SPST, Normally Open, Non Adjustable Operating Pressure: (+.05 +.02” W.C.) Maximum Pressure:1/2 PSI Operating Position: Diaphragm must be vertical Operating Temperature Range:-40 to 180oF Dimensions:5.75” x 4.5” Across Bracket, 2.75” High