Supplies the control circuit from the equipment power supply. Many conventional systems use nominal 24 VAC controls; communicating equipment may use a different supply.
8 cause articles →THE HVACSIM FIELD ENCYCLOPEDIA
Troubleshooting reference library
A part-by-part reference for troubleshooting: what can fail, why it looks that way, what separates it from a similar fault, and how to verify the repair.
Reference for HVACSim’s current components and related failure causes.
38 components & systems110 cause articlesLinked to the practice board
Mini-splits & all-in-one heat pumps
Brand references and guides for inverter systems, multi-zone equipment and monoblocks, including Ephoca / INNOVA.
Browse the ductless brand library →Choose a component, or search to find a specific cause.
Carries power and calls between thermostat, indoor controls and outdoor equipment. Terminal function comes from the diagram, not wire color.
4 cause articles →Protects the low-voltage circuit against excessive current. The holder must also make a reliable connection.
2 cause articles →Requests heating, cooling, fan operation and, on compatible systems, reversing-valve and stage commands.
3 cause articles →Uses a control signal to switch the outdoor unit's power circuit.
3 cause articles →Provides the phase-shift function required by applicable PSC fan and single-phase compressor circuits.
3 cause articles →Provides the outdoor service isolation point and, where fitted, branch protection through line fuses.
2 cause articles →Protects the circuit within the equipment and wiring design; its handle position is not a voltage test.
3 cause articles →Completes the line-voltage circuit between branch supply, controls and motors.
3 cause articles →Raises refrigerant pressure and circulates refrigerant; its motor, protection and mechanical pumping function are separate diagnostic questions.
4 cause articles →Moves outdoor air through the heat-rejection coil in cooling operation.
3 cause articles →Moves conditioned air through the indoor coil and distribution system.
3 cause articles →Switches blower power or a documented blower-enable path when a fan command is present.
2 cause articles →Interrupts a documented circuit when the service panel is removed or incorrectly seated.
2 cause articles →Removes cooling condensate and stops the documented circuit when overflow protection operates.
2 cause articles →Transfers indoor heat to refrigerant while the air path and filter maintain usable airflow.
2 cause articles →Rejects heat to outdoor air during cooling. On a heat pump its role changes with operating mode.
2 cause articles →Provides the working fluid and sealed path for heat transfer. Charge diagnosis combines equipment state, airflow, pressure and temperature.
4 cause articles →Controls refrigerant admission to the evaporator; a TXV responds to superheat rather than directly controlling suction pressure.
3 cause articles →Directs refrigerant flow between heating and cooling using a pilot solenoid and the main valve assembly.
3 cause articles →Coordinates defrost logic and the documented reversing-valve and fan outputs on applicable heat pumps.
2 cause articles →Detects specified refrigerant conditions and commands the model's protective response on equipped systems.
2 cause articles →Coordinates thermostat demand, board outputs, compressor modulation and matching airflow on applicable staged systems.
2 cause articles →Matches equipment output, airflow and control behavior to the building load and approved indoor/outdoor combination.
2 cause articles →Converts the supply into the controlled motor power used by variable-speed compressors. Input supply, DC link, output module and cooling are distinct diagnostic stages.
3 cause articles →Carries the documented power and communication paths between indoor units, outdoor controls and optional distribution equipment.
3 cause articles →Provides room, coil, piping, outdoor-air and discharge-temperature inputs used for demand, protection and refrigerant control.
3 cause articles →Meters refrigerant under controller commands, often responding to several measured temperatures and operating states.
3 cause articles →Moves air across indoor and outdoor coils using model-specific motor drives, feedback and air-direction controls.
3 cause articles →Routes indoor cooling condensate through gravity drains or approved lift pumps and prevents condensation outside the intended pan.
3 cause articles →Connects a matched split-system refrigerant circuit through approved piping or dedicated precharged connections.
3 cause articles →Coordinates several indoor units sharing outdoor capacity, piping circuits and the permitted mode logic.
3 cause articles →Requests operating mode, setpoint and supported features through local, wired, wireless or optional thermostat interfaces.
3 cause articles →Manages frost removal and cold-weather heating through coordinated sensing, compressor control, fans and refrigerant routing.
3 cause articles →Routes outdoor heat-exchanger air through the wall openings, adapters and external louvers of a single-package system.
3 cause articles →Manages water within a single-package heat pump through the model’s drain arrangement and any fitted disposal accessory.
3 cause articles →Provides the installed system’s specified outdoor-air ventilation and energy-recovery function where an ERV module is fitted.
3 cause articles →Uses the supported AC and/or photovoltaic inputs on purpose-built hybrid mini-split equipment.
2 cause articles →