Arkansas HVACR NewsMagazine May 2025 Issue

HVACR NewsMagazine May 2025

Tech News

Another common rule of thumb is that suction pressure will be close to the outdoor temperature in an R-22 system. This rule is totally a fluke and has no scientific basis other than it just generally tends to work out that way. On a properly functioning R-22 system running in heat mode in 40-degree weather, the suction pressure tends to be around 40 PSIG. This guideline obviously doesn't work on an R-410A system or any other refrigerant. temperature. If it is 50˚ outside, the suction saturation temperature would generally be between 25˚ and 30˚ on a functioning system. Remember that in heat mode, the colder it gets outside, the lower the suction pressure, and the hotter it gets inside, the higher the head pressure. Since the roles of the coil are reversed in heat mode, if you notice an abnormally high head pressure, it may be due to a dirty air filter or evaporator coil. A dirty condenser coil would cause the suction pressure to drop below normal. It may also cause superheat problems. Once a charge is set, whether by manufacturer specification or an alternative method, you can still verify the subcool and superheat on the unit in some cases. Do not confuse the superheat or subcool methods recommended by the manufacturer when running in heat mode. These are only used for setting the charge in cooling mode and not in heat. Look for heat mode-specific or low ambient guidelines. Finally — and most importantly — is ALWAYS TEST EVERYTHING. Airflow, delta T, superheat, subcool, suction pressure, head pressure, amps, incoming voltage, filter, etc. A more applicable guideline is 20- 25˚ suction saturation below outdoor ambient

Read manufacturers' specs and understand the units you are working on. Only then will guidelines and rules of thumb help instead of hinder you. — Bryan This article was furnished by the generosity of Bryan Orr, HVAC School by Techs for Techs. We encourage you to subscribe to their podcast and articles at https://hvacrschool.com/

Act 746 Signed by Governor Read the Article, “Big Changes Are Coming” Page 5