How to test a Pressure Sensor (MPC or Connect)

Pressure Sensor Test:

If you are getting High Pressure or Service Prefilter alarms, check the sensors as follows. The pressure sensors connect to the PC board at a green phoenix pin. The sensor has three wires; a positive (red), negative (black), and signal wire (white). On MPC systems the wires plug into pins labeled P, G, and S. On Connect systems the wires are labeled 5V, GND, and PRES.

Note: You will have to look at the wiring schematic in the user manual to see which PRES you need to use, as this depends on which sensor you intend to test.

The voltage on the white signal wire varies from .5 to 4.5 volts from 0psi to full range. Check to make sure you have 5 volts on the red (positive) wire. With the system running in run manual and the pressure relief valve open you should see around 0.5 VDC on the white (signal) wire. Then when you close the pressure relief valve the voltage should increase. To test without a system, you could hook it up to power and watch for the voltage to increase when acted upon by outside forces (like strongly blowing through the hole).


It is also be worthwhile to clean a pressure transducer that seems like it is acting up. Obstructions at the connection site creates resistance which can impact the reading. Below is a picture of brand new transducers as well as some older, dirty transducers.


Note: Pressure Transducer = Pressure Sensor