Mike PleziaInside service technician, Clark Associates · Commercial Equipment, HVAC, and Refrigeration professional

Pressure and Temperature Are Locked Together #hvac #refrigeration #tradetips

21 Aug 2026 · 1 min

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1:19

In this concise instructional segment, the speaker explains that refrigerants, like water, have a fixed relationship between pressure and temperature known as saturation. Changing pressure shifts the boiling/condensing temperature, which can be read on a pressure‑temperature (P‑T) chart to determine the expected refrigerant temperature inside a coil. The chart only applies when liquid and vapor coexist; when the refrigerant is entirely liquid (subcooled) or entirely vapor (superheated), the chart no longer predicts temperature. Understanding these concepts lets technicians interpret gauge readings accurately and apply the knowledge in the field.

Chapters

Hey, are you new to the trades? Here's something you may not know about pressure and temperature in the refrigeration. Water boils at 212 degrees, correct? Not always. Climb a mountain and it boils lower. Pressure changed, so the boiling point changed. Refrigerant works the exact same way. At any given pressure, that refrigerant is going to boil or condense at one specific predictable temperature. Change the pressure, and you change that temperature. That's the whole idea behind saturation— pressure and temperature are locked together. So, how do you use that in the field? The P-T chart is your decoder. You read a pressure off your gauges, you look it up on the chart, and it hands you the temperature that refrigerant should be at right now inside that coil. But here's the catch: that chart only works when liquid and vapor are hanging out together in the same space. Once refrigerant is fully liquid and colder than that saturation point, we call it subcooled. Once it's fully vapor and warmer than that saturation point, we call it superheated. Neither of those follow the chart anymore; only the mix in between does. Get that straight, and half of your gauge reading suddenly makes sense. Now that you know, you can help someone else.