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Lennox · Air conditioner

E601 Low ambient operational lockout

Low severity

What the control is telling you

Low ambient lockout on the outdoor unit. It won't start at 4 F (-15.6 C) or colder; if already running it keeps going until the call ends or outdoor temp falls to 15 F (-9.4 C). Dealer info. S30/S40 alert code 601; unit control shows E601.

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

Likely causes

  • Outdoor temperature below the unit's limit

Test and repair steps

  1. No repair needed; check the outdoor sensor if the reading seems wrong.
  2. Clears when temperature rises.

Settings for these units

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.46. Summarized in our own words; check the original manual for your model.

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