Short #67 - Defrost Termination and Failsafe

Short #67 – Defrost Termination and Failsafe

August 13, 2019

In this episode we quickly cover the words termination and failsafe and what they mean in relation to refrigeration defrost

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In this short podcast episode, Bryan covers some common mistakes when measuring static pressure. Static pressure is balloon pressure, not CFM or velocity pressure, but it can be an airflow indicator. The best way to start learning about static pressure is to start measuring total external static pressure.

Gas furnaces and heat pumps are different; static pressure is rated at the furnace in the former (not the cased coil, which is additional), and the static pressure includes the coil in a heat pump. The highest static pressure will always be at the blower, but restrictions on either side of the blower will raise static pressure on both sides of the blower.

Dirty components can drop the total external static pressure, which is a common point of confusion that can lead to misdiagnosis. You’ll want to determine static pressure at the blower and across components. If you want to determine if a cased evaporator coil is clogged, you can measure the static pressure drop across the coil (by measuring below and above the coil) and compare it to the manufacturer’s specifications. Dirty blower wheels can also cause problems, as they don’t move much air in the first place.

Lower static pressure at the blower is the best for amp draw and airflow, and our system designs and accessories can support low static pressure. Dialing in airflow, putting your probes in the right positions when you measure static pressure, proper register and grille selection, and minimally restrictive filters all go a long way.

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