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[43]

Error 43 — Open low pressure switch

Lennox · EL18KSLV Series Outdoor Units

What does [43] mean?

The low pressure switch circuit has been detected as open for 60 seconds (after 5 minutes of compressor run time) or for 30 seconds during standby. This suggests a problem with system pressure or the switch.

Common Causes

  • Incorrect pressure switch wiring.
  • Abnormal system pressure.
  • The system is clogged.
  • Incorrect refrigerant charge.
  • A valve is malfunctioning.
  • The pressure switch is faulty.
  • The main control board (PCB) is faulty.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Power off the unit and check if the pressure switch connection is secure.

  2. 2

    Use a multimeter to check if the low pressure switch terminal is short-circuited.

  3. 3

    Check if the Electronic Expansion Valve (EEV) coil is fixed well.

  4. 4

    Ensure the stop valve is open.

  5. 5

    Use a multimeter to check the resistance of Tc, Te, and Ts.

  6. 6

    Inspect the piping system for clogs and clean if necessary.

Browse all codes in this manual (43)
Verified technical data. Last updated: April 2026

Related Faults

1Error 1 — EEPROM malfunction or damage10Error 10 — Outdoor defrost sensor failure11Error 11 — Suction temperature sensor failure
Source: Lennox EL18KSLV Series Outdoor Units
Open Manual (Page 77)Search more codes in this manual