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Lennox · Heat pump

E422 Compressor top cap switch open

Medium severity

What the control is telling you

Compressor top cap thermal switch exceeded its limit. S30/S40 thermostat alert code 422 (shown as E422 on the unit control display).

Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems

Likely causes

  • Condenser fan, TXV or indoor blower problem
  • Stuck reversing valve or clogged filter drier
  • Loose top cap switch wire (XC/XP25)

Test and repair steps

  1. Check condenser fan motor, TXV and indoor blower.
  2. Check for a stuck reversing valve or clogged refrigerant filter.
  3. XC/XP25 make sure both top cap switch wires are on the TP terminals of the outdoor control.
  4. Check superheat and subcooling.
  5. Clears when corrected.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.32. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.