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PH91

PH91 — Low temperature protection of Evaporator

Lennox · Air Conditioning

What does PH91 mean?

The evaporator coil has reached a low temperature, potentially leading to freezing. This protection prevents ice buildup.

Common Causes

  • Low refrigerant charge
  • Restricted airflow across the evaporator
  • Dirty air filter
  • Outdoor unit issues affecting heat transfer

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check and clean the air filter for the indoor unit.

  2. 2

    Ensure there are no obstructions blocking airflow into or out of the indoor unit.

  3. 3

    Verify that the system is operating in cooling mode if temperatures are appropriate.

  4. 4

    Contact a technician to check refrigerant levels and airflow.

Browse all codes in this manual (57)
Verified technical data. Last updated: April 2026

Related Faults

E0E0 — Indoor unit EEPROM error (MMDB Indoor Units)E1E1 — Communication error between indoor and outdoor units (MMDB Indoor Units)E3E3 — Indoor fan speed error (MMDB Indoor Units)
Source: Lennox Air Conditioning
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