Massey Ferguson AC28 – Air Conditioning Control Module: Overvoltage

The system has detected that the voltage at the module's connectors is exceeding the maximum allowable operating threshold.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 7600 Series
• 8600 Series
• 8670
• 8690
• 5400 Series
• 6400 Series
• 7400 Series

1. 1

   Test the tractor's battery and alternator output with a multimeter while the engine is running to check for a faulty voltage regulator causing a system-wide overvoltage spike.

2. 2

   Inspect the Air Conditioning Control Module's yellow connector (X440) and blue connector (X439) for water ingress, corrosion, or bent pins bridging a high-voltage supply line to a lower-voltage signal pin.

3. 3

   Use a multimeter to test the supply voltage pins at connectors X439 and X440 for a short to power in the cab wiring harness, tracing lines back to the fuse box and A/C relays.

4. 4

   If the alternator is charging correctly (~14V) and the wiring harness shows no shorts, verify if the Air Conditioning Control Module has suffered an internal failure.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery terminal to prevent electrical spikes during repair.

2. 2

   Access the Module

   Remove the necessary cab trim/console panels to access the Air Conditioning Control Module.

3. 3

   Repair Wiring/Charging System

   If your diagnostics revealed a short to power in the harness, splice and repair the damaged wires using OEM-grade heat-shrink connectors. If the alternator was overcharging, replace the alternator assembly.

4. 4

   Replace the Module

   Disconnect the blue (X439) and yellow (X440) connectors. Unbolt the faulty Air Conditioning Control Module and install the replacement unit.

5. 5

   Reassemble and Clear Codes

   Reconnect the X439 and X440 connectors. Reinstall the cab trim panels. Reconnect the battery.

6. 6

   Test

   Start the tractor, clear the inactive AC28 fault code using a diagnostic tool or the dash interface, and run the air conditioning to verify the code does not return.