What happens
The actuator cannot execute a valid controller command because the electrical path or drive is impaired.
Typical symptoms
A zone has abnormal feed or a documented valve-circuit fault; other zones may operate normally.
Checks that distinguish this cause
Confirm the relevant valve, connector and controller output. With safe isolation, evaluate the separated harness and coil according to its pinout, then use the approved initialization and service-tool procedure.
What can look similar
The controller may intentionally restrict feed due to another sensor or protection input.
Repair direction
Repair the verified connection or replace the approved failed serviceable coil or controller component.
Verify the repair
Confirm the prescribed initialization and a corresponding stable refrigerant response.
Equipment-specific limits
A commanded step count is not proof of actual valve position. Coil pinouts, drive signals, initialization and resistance limits depend on the installed assembly.
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.
- Daikin: 17 Series service manualModel-specific sensor and control examples; terminal values and code definitions vary.
- Senville: R-454B model documentationSeparate installation and service documents for indoor styles and multi-zone generations.
Editorial review: 2026-09-29. Verify the current manual for the installed model.