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Deep Technical Chapters · Charge & Metering
Subcooling
Technician
Condensing temperature minus liquid line temperature. Tells you about charge and liquid-line restriction.
Subcooling is how much the liquid has been cooled below its condensing temperature. It tells you whether you have a solid column of liquid reaching the metering device.
What it tells you
High subcooling = overcharge or a liquid-line restriction. Low subcooling = undercharge or flash gas. Pair it with superheat to split charge vs restriction.
Field Rules
- 01
"High subcooling + high superheat = restriction before the metering device. Low subcooling + bubbles = low charge."
Diagnosis at a glance
Symptoms of failure
- •High: overcharge, restriction
- •Low: undercharge, flash gas
Measurements to take
- •Head pressure / condensing temp
- •Liquid line temperature
