1) Refrigeration & Heat-Pump Basics

  • Vapor-compression loop: compressor → 4-way valve → indoor/outdoor heat exchangers → expansion device → accumulator.

  • The 4-way valve reverses the circuit to provide cooling or heating.

2) Major Components — Purpose & Checks

  • Compressor: raises pressure/temperature and circulates refrigerant.

  • Heat exchangers (indoor/outdoor): reject/absorb heat; ensure free airflow and clean fins.

  • Strainer & capillary/EEV: meters refrigerant; watch for debris or restrictions.

  • Accumulator: protects the compressor from liquid flood-back.

3) Control & Operating Modes

  • Modes: Cooling, Heating, Dry, Fan, Auto.

  • Auto mode selects cooling or heating based on room temperature and setpoint.

  • Timers (On/Off/Sleep/Program) adjust operation and setpoint trajectories.

4) Indoor Airflow Management

  • Cooling/Dry: fan speed steps based on room/setpoint delta.

  • Dry: intermittent indoor-fan operation synchronized with compressor cycling.

  • Heating: fan ramps with coil temperature to prevent cold draft.

  • Louvers: default horizontal in cooling/dry and downward in heating; swing ranges vary by model.

5) Room-Temperature Control Logic

  • Controller compares room temperature (TR) to setpoint (TS) and sequences compressor, outdoor fan, and indoor fan.

  • Anti-short-cycle timers (typically ~3 minutes) protect the compressor from rapid restarts.

6) Automatic Protections

  • Anti-icing (cooling): reduces frequency or pauses to avoid indoor-coil freeze.

  • Heating overload: staged responses as indoor-pipe temperature rises.

  • Cold-draft prevention: delays/limits indoor fan at heat start-up.

  • Auto-defrost: frost judgement triggers valve shift and controlled defrost, then resumes heating.

7) Indicator Lamps & Thermistors

  • Lamp behavior tables classify faults for first-pass triage.

  • Thermistor reference tables (room/pipe, outdoor coil/ambient, discharge) support bench testing and verification.

8) Troubleshooting Framework

  • Root-cause domains: operation misuse, environment, installation, maintenance, electrical circuit, and refrigerant system.

  • No operation / no lights: check supply, fuses, low-voltage rails, reset circuit, and controller inputs.

  • Indoor fan inoperative: inspect capacitor/coil, bearings, drive components, and controller output.

  • Outdoor fan inoperative: confirm drive signals and motor health.

  • Compressor inoperative: verify relays/drives, overloads, terminal voltages, and mechanical condition.

  • Poor cooling/heating: assess airflow, load, charge, restrictions; use ΔT and pressure reasoning.

  • Noise/Vibration: check mounting, piping contact, fans/bearings, 4-way valve, compressor mounts.

  • Water leakage (cooling): check leveling, drain route, trap, and filters.

9) Installation Highlights (Legacy Guidance)

  • Match capacity to room size; respect maximum line lengths and height differences.

  • Calculate additional refrigerant charge vs pipe length where required.

  • Follow flaring/connection procedures and correct flare-nut torque values.

10) Service Best Practices

  • Respect anti-short-cycle timers before restarting.

  • Log baseline commissioning data (pressures, ΔT, fan speeds, input current).

  • Validate thermistors against reference tables before replacing PCBs.

  • Treat icing/overload and defrost events as normal protective behavior unless persistent under nominal conditions.