Non-condensables collect at the top of the condenser, taking up surface and raising head pressure, compressor amps and discharge temperature; air also brings moisture and oxygen that form acids. They come from poor evacuation or leaks on the low side running in vacuum. A system at rest with pressure well above the PT value for the ambient temperature is a giveaway. The fix is recovery, repair, evacuation and a new charge.
Head pressure's 40 pounds high with a clean coil and standing pressure is way over PT, we've got non-condensables.
Let a system sit off for a while, then compare its pressure to the PT chart at ambient; extra pressure means extra gas.
Also heard as
- noncondensables
- non-condensable gases
- NCG
Related terms
Head pressure
The compressor discharge or condensing pressure of a refrigeration system.
Pull a vacuum
To evacuate a refrigeration system with a vacuum pump, removing air and moisture before charging.
PT chart
Pressure-temperature chart: a table giving each refrigerant's saturation temperature at each pressure.
Recovery
Removing refrigerant from a system into a recovery cylinder instead of venting it to the atmosphere.