Arkansas HVACR NewsMagazine May 2026

HVACR NewsMagazine May 2026

Tech News

If you simply want to confirm that the unit is functional, you can take an evaporator delta T and measure the liquid line and suction line temps at the evaporator to approximate proper operation. You will not be able to “set the charge” until the condenser coil has been allowed to dry completely. The liquid line will generally be around the outdoor temperature. It may even be a bit lower, depending on the SEER of the unit and how wet the coil is. (Wetter/higher SEER = cooler liquid line.) The suction line will be approximately the return temp minus 40°F (4.44°C) + the desired superheat +/- 5°F (2.75°K). It will tend to be on the lower side of the evaporator temperature scale because of the lower liquid pressure. measurements and not just walking away from a system without doing appropriate testing. However, if it's raining, you're just not going to get good readings. You also risk doing more harm than good to the system by taking those readings. Sometimes, taking fewer readings can be the best call. When it's raining, I would rather have my techs note the delta T, indoor liquid line temp, and suction line temp with a note about “raining” than risk an issue by connecting in the rain. In cases where we have to set a charge, we will need to return and set the charge once the weather is dry. In cases where we did a simple drain cleaning, replaced a blower wheel, replaced a thermostat, or replaced a capacitor, those indoor readings will suffice. Are they conclusive? NO! Would I rather contaminate a system? Nope. Should we return to every My Opinion If you read our articles, you know that we are huge advocates of taking accurate

system the next day to check the charge with gauges just because it was drizzling? I say no to this as well. You may say (as many do) that connecting while raining has never caused issues for you before. To that, I would say: how do you know? It's not like systems spontaneously combust when moisture enters them. The result is long-term damage that could never be traced back to the initial cause. It was also less of an issue when mineral oil was the prevalent oil in use. You can read more about refrigerant oil and why it matters HERE. Am I saying that you can never check a charge even in a light sprinkle? No. Just use common sense. Don't be a robot that ALWAYS connects gauges, especially when it'll likely do more harm than good.

— Bryan

This article was furnished by Brian Orr and HVAC School For Techs by Techs. We appreciate them sharing their excellent articles and encourage our readers to subscribe to their site at https://hvacrschool.com/start/

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