System Refrigerant Charging
System Evacuation
Perform a deep evacuation of the system. Ensure all valves are open and that there are no parts of the system are
isolated. Replace any Schrader caps to ensure no leaks through the core. A Schrader core may open due to the
evacuation.
Once the evacuation is complete perform a vacuum check. Any loss of vacuum must be investigated.
Breaking the System Vacuum
Break the vacuum of the system until the standing pressure of the refrigerant is achieved. Charge through the liquid line
until 75% of the refrigerant is in the system.
Carefully remove the vacuum gauge.
Before running a system, check that the controller is measuring values correctly. Ensure the correct refrigerant is
programmed into the strategy. Check with manifold gauges and temperature sensors that they read consistent.
When satised that the system measurements are correct turn the system on and continue charging through the
expansion line.
Charge the system in the liquid state. In no more than 0.5kg increments.
Any more refrigerant charge in any one step could overcharge the system very rapidly and cause liquid ood back to the
compressor.
Operation Checks
When operating a refrigeration system that uses inverter technology the following checks are required.
The system can be checked to ensure correct operation by measuring the following:
• Evaporator Superheat
• EEV Sub cooling
• Condenser Liquid Drain Sub cooling
• Oil Sump Temperature
Evaporator Superheat
The evaporator superheat ensures that liquid refrigerant does not enter the compressor. The superheat value is
programmed into the expansion valve. Too high superheat indicates a low refrigerant charge. Too low superheat could
indicate the system being overcharged.
Condenser Liquid Drain Subcooling
Check that the liquid drain sub cooling is constant. If the sub cooling temperature uctuates it indicates signs of the
condenser lling and draining. Too high sub cooling could indicate that the condenser is backing up with liquid. The
condenser heat rejection performance is reduced and could cause high pressure trips.
EEV Subcooling
This is the true sub cooling on a system. Subcooling ensures a full column of liquid to the expansion valve.
If a sight glass is available check that the indicator is clear and not ashing. If a sight glass is not tted check with your
stethoscope.
You will hear a steading ow of refrigerant. Pulsing indicates that the liquid line is ashing.
The EEV sub cooling could be higher if the system has gained sub cooling from the ambient.
Sub cooling will be affected by the ambient temperature. If the temperature is low the provision of a LAK or ELAK may
be required. See LAK / ELAK documentation.
Oil Sump Temperature
Ensure the compressor sump has a minimum of 10K discharge superheat*.
When the system is running at full load the superheat will be higher. At part loads the superheat will be lower.
Below 10K discharge superheat the compressor may be slugging liquid. Liquid ood back can cause the oil in the
compressor to dilute causing foaming in the compressor causing bearing wash and seizure.
Above 35K the system may be undercharged. Oil within the compressor could break down with the heat.
Always ensure the discharge gas superheat can reduce when the system goes into part load no lower than 10K.
*Discharge superheat = Condensing Temperature – Discharge Line Temperature
For example: 45°C Condensing Temperature – 70°C Discharge Line Temperature = 25K Discharge Superheat
To Next Page
Loading...
