Pressure Transducer Explanation and Testing
Use this reference to understand the purpose of the pressure transducer and to check its power supply, return voltage and diode-test readings.
Pressure transducer function: The pressure transducer is used to monitor high or low operating pressure. It operates from a 5 V DC supply and is connected directly to the Main / Controller PCB. The PCB uses the transducer return voltage to determine operating pressure.
1. Pressure transducer overview
| Item | Reference |
|---|---|
| Purpose | Monitor high or low operating pressure. |
| Operating voltage | 5 V DC |
| Connection | Connected directly to the Main / Controller PCB. |
| Pressure calculation | The return voltage is used by the PCB to determine operating pressure. |
| Pipe connection | Most transducers are fitted to a Schrader core; some VRF outdoor units have the transducer brazed into the pipework. |
2. Power-on voltage test
With power on, check the three-wire pressure transducer circuit at the sensor or Main / Controller PCB connection.
| Measurement | Expected reading | Function |
|---|---|---|
| Red to Black | 5 V DC | Pressure transducer power supply. |
| Black to White | Return DC voltage | Signal used to calculate operating pressure. |
Examples shown in the training material:
- 1.14 V return voltage corresponds to approximately 800 kPa.
- For the discharge pressure example, 2.5 V return is approximately 2500 kPa.
- The Mobile Technician pressure sensor conversion example shown is 2.800 V = 2875 kPa.
Important: Use the relevant pressure-transducer conversion information for the unit being tested. The examples above are the values shown in the training reference.
3. Power-off diode test
With the system powered off and the pressure transducer unplugged, set the multimeter to diode test and compare the readings with the following reference.
| Black meter lead | Red meter lead | Expected value |
|---|---|---|
| Black | White | 1.0 V to 1.1 V |
| Black | Red | 1.2 V to 1.3 V |
| White | Red | 1.6 V to 1.7 V |
| White | Black | 0.6 V to 0.7 V |
| Red | Black | 0.5 V to 0.6 V |
| Red | White | 0.6 V to 0.7 V |
| Earth | Red | O/L |
| Earth | White | O/L |
| Earth | Black | O/L |
4. Quick diagnostic sequence
- Identify whether the transducer is monitoring the high-pressure or low-pressure side.
- With power on, confirm 5 V DC between Red and Black.
- Measure the Black-to-White return voltage.
- Compare the return voltage with the relevant pressure conversion information for the unit.
- If further confirmation is required, isolate power, unplug the transducer and perform the diode-test checks above.
- Compare each diode reading with the expected values and confirm all three wires show O/L to earth.
Electrical safety: Power-on voltage measurements and service checks must only be carried out by appropriately qualified service personnel using suitable test equipment and safe electrical work practices.