Testing the Pressure Switch Transducer
The main thing to understand is that the pressure transducer is fed 5VDC from the circuit board. It then send back to the board .25VDC at 0”WC. So if the inducer is not running you will see .25VDC coming back from the transducer. Once the inducer motor starts the voltage on the pressure transducer will increase. On the 96% furnaces the pressure transducer max is -2”WC at 4VDC on the 80% furnaces the max is 4”WC at -4VDC. You can verify the pressure transducer is working properly by holding down the SW1 button for more than 10 seconds less than 15 sec. The Led will flash rapid amber and the unit will go into a test mode. Shown below. Check for .25VDC before the inducer starts then watch the voltage rise and the inducer increases. In the test mode the negative pressure will be half what the max is. For example on at 96% furnace the inducer will ramp up to 1”WC and on the 80% furnace it will ramp up to 2”WC. This will give you a good gage on what voltage you read coming back from the pressure transducer.