Arkansas HVACR NewsMagazine May 2025 Issue

HVACR NewsMagazine May 2025

Tech News

Step 7: Conclusion:

If you want to learn more about measuring static pressure and pressure drop, watch this video:

0.67” WC is an extremely high pressure drop to have on a system which tells us that there is some sort of blockage on the underside of the coil. This must be cleaned in order for the system to operate correctly with proper airflow. Normally, the highest pressure drop that a manufacturer may specify are 0.4 or 0.5" WC. However, a typical static pressure drop will usually be between roughly 0.1 0.35” WC. This is a dry pressure drop reading because the outdoor unit is not powered so no refrigerant is cycling through the coil causing humidity to condense onto the coil. A wet coil pressure drop may be roughly .05" WC higher than a dry measurement. Evaporator coil manufacturers list both a dry and wet coil pressure drop in "WC, based on the airflow CFM crossing the coil. Compare the actual "WC pressure drop to the manufacturer's data pressure drop to see if the unit is in spec. If the actual "WC measurement is higher or significantly higher, the underside of the coil needs to be cleaned by moving it to get access or recovering the refrigerant in order to remove and clean it. Sometimes, there is a front panel on the coil which can be temporarily removed for cleaning. If the static pressure measurements check out and are within spec, it may be possible that another airflow problem exists such as in the return ducting. Make sure to turn the power off and remount the safety switch and turn back on the outdoor disconnect. Then make sure to turn the furnace back on and test both heat and ac before leaving the jobsite.

About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”.

Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 17 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel Act 746 Signed by Governor Read the Article, “Big Changes Are Coming” Page 5