H7: Compressor Desynchronization or Sensor Malfunction
H7 TROUBLESHOOTING STEPS:
STEP 1: Verify Line Voltage
TIPS:
-
Measure between L1-L2 to confirm proper input voltage as rated on the data plate.
DISCONNECT POWER TO OUTDOOR UNIT
STEP 2: Evaluate the Installation
TIPS:
-
Assess cleanliness of indoor filters, coil, and blower wheel.
-
Check condenser and ensure adequate space for airflow.
-
Examine outdoor unit's space for proper airflow.
-
Confirm open service valves and proper evacuation for new installations.
-
For multizone systems, check wiring and line sets for correct matching.
STEP 3: Was Main Board Replaced?
TIPS:
-
Verify proper procedures were followed during the board replacement.
-
Ensure wiring from Main board U, V & W matches with compressor U, V & W.
-
Review wiring schematic on the unit or service manual.
STEP 4: Perform compressor ohm check
TIPS:
-
Unplug compressor from the main board.
-
Set the meter to 0-200 Ohm scale or auto range.
-
Check resistance from U to W, U to V, and V to W (typically between 0.6 and 2.0 Ohms).
-
Check ohms U, V, and W to ground resistance (should be infinite or OL).
STEP 5: Perform Thermistor/sensor check
TIPS:
-
Verify thermistor readings using the Thermistor Temperature to Resistance Table. See Thermistor Temperature to Resistance Table.
STEP 6: Restart system
RESTORE POWER TO OUTDOOR UNIT
STEP 7: Does the compressor run? No
TIPS:
-
Check amperage on each wire to the compressor.
-
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
TIPS:
-
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