Control does not see its own send message: the integrated furnace control is not seeing the blower-communication send.
Likely causes
- The control's own blower-communication send path has failed
- Harness or wiring, if the code changes to E17 when the 4-pin connector is removed
Safe checks for E18
- Do not unplug the blower harness with the power on. The chart's test is done with power on, inside a live cabinet
- Technicianwith power on, remove the 4-pin motor connector from the IFC. If the code changes to E17, verify the harness and wiring. If it does not change, replace the IFC
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician. E18 is the control not seeing its own send message. E17 is the control not seeing the motor's reply.
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Parts & tools for this fix
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Furnace blower (circulator) motor: guide
In this code: The control's own blower-communication send path has failed
This one is for a technician to test or replace, so we only explain it and do not link to buy it.
Furnace control board and low-voltage fuse: guide
In this code: Parts list for this code: Integrated furnace control
This one is for a technician to test or replace, so we only explain it and do not link to buy it.