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Subcool Calculator

Calculate subcool for air conditioning systems to ensure proper refrigerant charge and optimal performance.

Subcool Calculator

Read from the high-side gauge on your manifold

Measure at the liquid line near the service valve or condenser outlet

What is Subcool?

Subcool is the difference between the saturation temperature of refrigerant and the actual temperature of the liquid refrigerant. It indicates how much the liquid has been cooled below its condensing temperature, which is essential for proper system charging and efficient operation.

How to Measure Subcool

  1. Connect your manifold gauges to the service ports
  2. Read the liquid line pressure from the high-side gauge (PSIG)
  3. Attach a temperature probe to the liquid line near the service valve or condenser outlet
  4. Record the liquid line temperature
  5. Use this calculator to determine subcool and charging status

Subcool Guidelines

Below 5°F:Too low - system is undercharged
5-8°F:Low - may need slight refrigerant charge
8-15°F:Optimal range for most systems
15-20°F:High - monitor for overcharge or airflow issues
Above 20°F:Too high - overcharged or restricted airflow

Subcool vs Superheat

Subcool is measured on the high-pressure side (liquid line) and indicates proper refrigerant charge.

Superheat is measured on the low-pressure side (suction line) and protects the compressor from liquid refrigerant.

Both measurements are essential for proper system diagnosis and charging.

Refrigerant Types

R-410A

Common refrigerant in modern mini-split and residential AC systems. Being phased out due to environmental concerns.

R-32

Newer, more environmentally friendly refrigerant with lower global warming potential. Increasingly common in mini-splits.

R-454B

Next-generation refrigerant designed to replace R-410A with significantly lower environmental impact.