Sub cooling is one of the best methods to determine if the refrigerant charge is correct. It is also a useful calculation for troubleshooting as it shows exactly what is happening in the condenser.
How to measure sub-cooling:
- Take high side pressure at the receiver. (On pressure gauge)
- Convert the high side pressure to temperature by using the pressure/temperature Comparator.
- Record the actual temperature of the liquid leaving the condenser with a surface temperature probe.
- Subtract the liquid pipe temperature (at the exit of the condenser) from the converted temperature (from the high side pressure using the pressure/temperature comparator).
- The difference is the amount of sub cooling
The sub-cooling value should be between 4-8K (kelvin) when the sub-cooling is under 4K then the system is undercharged and more refrigerant will need to be added.
When the system is over 8k then the system is overcharged with refrigerant and you will need to remove some of the charge in an environmentally friendly way until the sub-cooling value is correct.
Note: When taking sub-cooling measurements make sure that all condenser fans are on full speed and that the compressor is fully loaded.