Massey Ferguson 10.00.09 – AIRCON: Air Conditioning Evaporator Temperature Sensor Open Circuit

The control module is not receiving a valid electrical signal from the evaporator temperature sensor because the circuit is 'open.' An open circuit is typically caused by a broken wire, a disconnected wiring harness plug, or a sensor that has failed internally (infinite resistance). As a safety measure to prevent the evaporator core from freezing over, the system registers this fault, automatically turns off the air conditioning compressor, and disables cooling.

• 7724S
• 5712SL
• 7722
• 7722S
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7726S
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 4707
• 4708
• 4709
• 4710
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 7714 through 7726S
• 8670
• 8690

1. 1

   Live Data Monitoring: Connect a diagnostic PC/tool to the tractor and check the signal accuracy of the evaporator temperature sensor. If it reads an impossible default value (or extreme negative temperature), the circuit is open.

2. 2

   Visual Inspection: Locate the evaporator temperature sensor (often designated as component X443 in Massey Ferguson wiring diagrams). Inspect its electrical connector for corrosion, pushed-out pins, or a loose connection.

3. 3

   Wiring Harness Check: Inspect the wiring harness between the sensor and the AIRCON module for any visible breaks, chafing, or rodent damage.

4. 4

   Resistance Measurement: Unplug the sensor and use a multimeter set to Ohms to measure the resistance across the sensor's two pins. If the meter reads 'OL' (Open Loop) or infinite resistance, the sensor itself has failed and must be replaced.

5. 5

   Continuity Test: If the sensor tests good, check for continuity on the signal and ground wires from the sensor connector back to the AC module to locate the break in the wiring.

1. 1

   Turn off the tractor and disconnect the battery ground cable

   This prevents electrical shorts.

2. 2

   Access the HVAC unit

   Depending on your specific tractor model, this will require removing the inner cab roof panel or accessing the HVAC box under the seat/dash.

3. 3

   Locate the evaporator temperature sensor

   It is a probe that is inserted directly into the aluminum fins of the AC evaporator core.

4. 4

   Disconnect the electrical connector from the sensor

5. 5

   Carefully pull the old sensor probe straight out of the evaporator fins

   Do not bend or damage the delicate fins of the evaporator core.

6. 6

   Insert the new sensor probe into the exact same location in the evaporator core

   Ensure it is seated to the correct depth so it accurately measures the core temperature.

7. 7

   Reconnect the electrical harness

8. 8

   Reassemble the cab panels or covers

   Reassemble the panels or covers that were removed to access the HVAC unit.

9. 9

   Reconnect the battery, turn on the tractor, and clear the fault codes

   Use a diagnostic tool to clear the codes.

10. 10

    Turn on the AC system and verify operation

    Verify that the compressor engages and the system blows cold air.