Outdoor unit runs but indoor blower does not, or blower runs at incorrect speed, E7 logged on communicating systems

Safety first: Turn off power to the furnace/air handler at the breaker. ECM motors can start unexpectedly—never work with power on.

Steps:

• 1. Verify thermostat mode: Ensure the thermostat is set to COOL and FAN AUTO (or ON for continuous fan) and that there is a call for cooling.
• 2. Access blower compartment: Remove the blower door and locate the ECM motor and its control module.
• 3. Check harness connections: Inspect the multi-pin low-voltage plug and high-voltage plug at the motor. Reseat them firmly. Check the harness from the indoor control board to the motor for damage.
• 4. Inspect control board LED codes: Many Armstrong Air furnaces/air handlers display additional blink codes indicating motor faults. Note the pattern for reference.
• 5. Power cycle: Restore power with the blower door switch depressed or taped closed. See if the blower starts after a 1–2 minute delay.
• 6. If E7 persists and blower will not run: The ECM motor or its module is likely failed and must be replaced as an assembly. This is typically a professional repair due to setup and balancing requirements.