Preparations for VRF system before winter power-on
VRF (Multi-Split) Heating System Start-up Preparations (For systems restarting after long-term winter shutdowns, special attention should be paid to preventing liquid slugging)
Key point: Preheating the crankcase is the top priority. Starting the engine without preheating can easily lead to liquid slugging and compressor burnout .
I. Power supply & crankcase preheating (most important)
the main power switch for both the outdoor unit and all indoor units, and preheat for 6-12 hours in advance (most mainstream brands like Daikin, Hitachi, and Midea require ≥6 hours; 12 hours is recommended for low-temperature environments). This will activate the crankcase heater, heating the refrigerant oil and causing the dissolved liquid refrigerant to separate, preventing liquid slugging upon startup. After powering on , do not immediately turn on heating on the wired controller/outdoor unit mainboard ; simply maintain standby preheating. If there is a prolonged power outage, the preheating timer will reset, requiring you to wait the full preheating time again. During long winter usage periods, try to keep the main power supply on as much as possible and maintain standby heating.
II. Inspection of Refrigerant Piping and Valves
The high and low pressure shut-off valves (maintenance valves) of the outdoor unit must be fully opened and in the correct position. Starting the unit in a partially open or closed state is strictly prohibited (as this will cause pressure buildup and damage to the compressor). Visually inspect the piping insulation for damage and check for oil stains on the copper pipes, joints, and branch connectors (oil leaks equal refrigerant leaks). Confirm that the system has passed the previous pressure testing and vacuuming, and that the refrigerant charge level matches the nameplate (add refrigerant to the piping should be calculated according to length).
III. Outdoor Unit Inspection (Focus on Heating)
Outdoor unit heat exchanger: Clean away fallen leaves, debris, snow, and ice. If snow is thick, do not pry it off forcefully; use warm water (≤50℃) to melt it. Do not use boiling water or a spray gun to bake the fins , as this will deform the fins, reduce heat exchange, and cause frequent defrosting, high-pressure protection activation, and fault reports. Ensure adequate ventilation space around the outdoor unit to meet installation requirements; do not obstruct airflow with barriers or materials. Ensure the mounting feet and vibration damping pads are intact and not loose; the fan should rotate smoothly without jamming. Check that the defrost sensor and coil temperature sensor are properly installed and not detached.
IV. Indoor Unit Inspection
The filter screen is clean, and the return air and air outlet are unobstructed, with no jammed air outlet blades. Condensate drainage: The drain pump/drain pipe is unobstructed; a water drain test is performed to prevent condensate (in some heat recovery models) and defrosting overflow from flooding the ceiling during heating. Ducted units: The ducts are not dented, and the flexible joints are not damaged; static pressure and air outlet settings are matched. The wired controller/central controller communicates normally, with no communication fault codes; the indoor unit address and master/slave unit settings are correct (for multi-split network units).
V. Electrical Inspection
The three-phase voltage is balanced and within the rated range. Do not start the machine if one phase is missing or the voltage is too low. Grounding is reliable. Power lines and communication lines (RVSP shielded wire) are undamaged and not incorrectly connected. Communication line polarity is correct. All circuit breaker and contactor terminals show no signs of loosening or overheating.
VI. Pre-confirmation of Model and Environment
Confirm the unit's permissible heating range : For most air source heat pump (VRF) systems, heating capacity is significantly reduced when outdoor temperatures are too low (e.g., below -20°C), and some models do not support heating start-up; when outdoor temperatures are too high (>24°C), heating is generally prohibited and the unit will shut down as a safety precaution. For multi-split systems: Cooling and heating cannot be performed simultaneously within the same system (for ordinary heat pump types, non-heat recovery). Unify the mode of all indoor units beforehand. Clear historical fault codes on the controller and confirm there are currently no fault alarms.
VII. Power-on procedure (after preheating)
First, check the outdoor unit's main board and wired controller for fault codes. The wired controller should be set to heating mode, with the set temperature higher than room temperature (generally 24-28℃). After powering on, the indoor unit will initially activate its cold air protection mechanism , temporarily stopping the fan until the coils heat up before outputting hot air. This is normal logic and not a fault. During the initial startup phase, pay attention to: the outdoor unit fan's start/stop, the sound of the four-way valve switching, any unusual noises, and any frequent protection shutdowns.
VIII. Prohibited Activities
× Do not force heating if preheating time is insufficient.
× Start-up without fully opening the shut-off valve
× Do not start the outdoor unit without cleaning snow and ice buildup on the heat exchanger.
× Do not use boiling water or open flame to melt the frost and ice on the outdoor unit.
× The system is not operating in heating mode when there is a refrigerant shortage or leak.
PREVIOUS:
