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H5: IPM Module Synchronization and Over-Current Protection

Safety Note: Before any component is electrically disconnected in the unit, shut off main power. Inverter board DC bus voltage can take up to 15 min to discharge.

Caution: Do not plug or unplug components while electrical power is present, this can damage the equipment and control boards.


STEP 1: Evaluate the installation


  • Before addressing component failures, ensure the system and its components are clean, and there is adequate airflow through coils.

  • Confirm that all service valves are open, and the system was properly evacuated, especially in the case of multizone systems with proper piping rules.

  • Verify wiring matches the correct ports on the outdoor unit for each indoor unit. Additional charge amounts should be calculated and weighed in according to installation documents.


STEP 2: Check standing refrigerant pressure


STEP 3: Perform Electrical inspection


  • Check all wiring connections to the unit and main board following the wiring diagram.

  • Inspect the main board for any visible damage. If the main board has been replaced, proceed to Step 5.

STEP 4: Perform compressor ohm check


  • Unplug the compressor from the main board.

  • Use a multimeter set to the 0-200 Ohm scale or auto range to check resistance from U to W, U to V, and V to W. Values should be generally between 0.6 and 2.0 Ohms.

  • Set the meter to K Ohms and check ohms from U, V, and W to ground. Resistance should be infinite or OL.

IF MAIN BOARD WAS REPLACED, STEP 5: Main Board inspection


  • Ensure old thermal paste is cleaned off, and new thermal paste is applied. Verify that mounting screws are in place and properly tightened.

  • All screws must be reinstalled and torqued to facilitate heat transfer to prevent board overheating. Refer to Heat Paste Installation Instructions.

STEP 6: Restart system


STEP 7: Does the compressor run? No


  • Check the amperage on each wire to the compressor.

  • The compressor should attempt to start at least 3 times. In a normal cycle condenser fan will start, 30 to 60 seconds later compressor will attempt to start if it does not start the condenser fan will stop shortly thereafter and attempt again.

  • If amperage is read on each wire to the compressor, then the compressor is stuck.

  • If there is no amperage on one or more of the wires, then the mainboard has failed. Replace Main Board. See Heat Paste Installation Instructions.

STEP 8: Does the compressor run? Yes


  • Compressor starts, and amperage keeps increasing until H7 code is produced may take a while to produce the code.

  • Possible overcharge. See PT Chart.

  • Restriction or kinked refrigerant line. See 4-Point Temp Check Guide.

  • Inadequate airflow

  • Multizone Cross Piping or Crosswire

  • When compressors fail to pump, something within the machine has generally caused the compressor to fail ( undercharge, overcharge, restrictions, poor airflow ) Therefore if a compressor is replaced it is important to check operation thoroughly after replacement to identify the cause of the compressor failure.

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