Furnace Pressure Switch Tester

A furnace pressure switch is a safety device located near the draft inducer motor of a gas forced-air furnace. The switch is there to prevent the furnace from running unless the correct venting air pressure is present. Therefore, it is necessary to test each switch prior to installation in order to prevent failure. When compared to existing technology used to manually test each switch, Trane requested a device that would automate this process to reduce the time required to perform each test while simultaneously increasing data quality. For each test performed a pressure switch is connected to the device using a simple hose-to-barb connection that feeds directly into the apparatus. Our system is comprised primarily of two fans which can create positive or negative pressure as selected. We use PWM control to guarantee that the fans will steadily modulate at the desired rate. The pressure generated is monitored by using a high precision pressure sensor between the two fans. Whenever a test is completed, the exact value of each make and break point of the switch will be displayed for each cycle (up to three cycles). The make point is the pressure at which the switch closes (complete circuit) and the break point is the pressure that causes it to open. The hysteresis, defined as the difference between the values of the make and break pressure points, will also be calculated and displayed. The device will also determine and display whether the switch has passed or failed a tolerance test of its make and break points and a tolerance test of its hysteresis based on its trigger set point. The system components are protected by a 3D-printed PLA housing.