What happens
The ventilation module lacks a valid command, supply or functional fan circuit.
Typical symptoms
Ventilation is absent while the main heat pump continues operating.
Checks that distinguish this cause
Trace the module’s documented enable, power and fan status independently from the cooling controller. Use its diagnostic procedure before replacing a module or main board.
What can look similar
A permitted schedule or interlock may intentionally suspend ventilation.
Repair direction
Correct the proven command or connection defect, or replace the approved failed module component.
Verify the repair
Verify scheduled and commanded ventilation and the documented interlock behavior.
Equipment-specific limits
Not every all-in-one unit contains an ERV. Cooling airflow and ventilation airflow are different measurements; use the module’s filtration, balancing and maintenance requirements.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- INNOVA (formerly Ephoca): AIO technical resourcesChoose cabinet style, generation and accessories. Installation, maintenance and troubleshooting documents are separate.
Editorial review: 2026-09-29. Verify the current manual for the installed model.