What It Means
- OUTDOOR ENTHALPY SENSOR
Lennox Unit controller
Lennox Error Code 91
Unit controller
Causes & actions from Lennox
How it shows
- M4 alarm code: 91
• If Enthalpy Sensor failure is detected, the system will disable ‘Free Cooling’ operation. NOTE: Valid Outdoor Enthalpy Sensor reading is required for both ‘ODE’ (Outdoor Enthalpy) and ‘ODE differential’ (Outdoor differential). Valid Indoor Enthalpy Sensor reading is required for ‘ODE differential’ (Outdoor differential). • Check economizer Parameters 160 and 161. Also check enthalpy Parameters 162 and 163. • Check sensor and wiring.
Applicable models & manual sources
- MODEL L - M4 UNIT CONTROLLER
OUTDOOR ENTHALPY SENSOR
MODEL L - M4 UNIT CONTROLLER, M4 Unit Controller
Disclaimer: This information is for general reference. Code wording and instructions vary by model. Always follow the service manual for your exact unit.
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