If you work with modern blended refrigerants like R407C, R448A or R449A, you need to understand ‘temperature glide’. Getting it wrong leads to incorrect superheat and subcooling readings and mischarged systems.
What is glide?
Pure refrigerants boil and condense at a single temperature for a given pressure. Zeotropic blends are mixtures of refrigerants with different boiling points, so they change phase over a range of temperatures at a constant pressure. That range is the temperature glide.
Why it matters
- Two saturation temperatures: blends have a ‘bubble point’ (start of boiling) and a ‘dew point’ (end of boiling) on the P/T chart
- Superheat is calculated from the dew point
- Subcooling is calculated from the bubble point
- Using the wrong value throws your readings off and leads to mischarging
Charging blends
Always charge zeotropic blends as a liquid from an upright cylinder. Charging as vapour lets the lighter components leave first, changing the blend’s composition (fractionation) and its performance.
FAQ
Do all refrigerants have glide? No — single-component refrigerants (like R32) and azeotropic blends have little or none; zeotropic blends (like R407C, R448A) have noticeable glide.
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