Arkansas HVACR NewsMagazine May 2019

S tate, National, Chapter News Tech News

Freezing causes flood back, no cooling, water damage and biological growth. We cannot leave a system that is just going to freeze. The image to the left is of the Danfoss refrigerant slider app and it shows that when suction pressure drops below 102 PSIG on an R410a system…. the coil hits 32° and will start to freeze. This means that we need to setup equipment so that it will not freeze during normal operating conditions. A typical residential A/C system should be setup so that the return temp can get all the way down to 68° and still be just above freezing.

32° SATURATION (EVAP TEMPERATURE) Article Furnished by Bryan Orr,

Evaporator temperatures below 32° are common and acceptable in refrigeration, that’s why there is a defrost sequence. In a heat pump running in heat mode, it’s the same, freezing is a part of the process and defrost is necessary. In comfort cooling… we can’t allow the evaporator to get below 32°… or it will freeze. I can’t tell you how many times I look back at technician notes and can see in plain black and white that the system will freeze.

Let’s say it’s 78° in a house on an R410a system and your suction pressure is 108 PSIG (like shown) Your suction saturation (coil temperature) is 35°, and so the coil won’t freeze.

And that is not OK…