Arkansas HVACR NewsMagazine May 2025 Issue

HVACR NewsMagazine May 2025

Tech News

Below are steps in order to measure the static pressure drop across the evaporator coil Step 1: Turn the power off to the furnace and remove the front furnace cabinet cover. Next, locate the thermal limit switch. Here it’s easily visible, but it could also be mounted back behind the gas valve. Unscrew and remove the thermal limit switch from the hole. Place the switch and wire assembly in a location in a safe spot where it will be protected when the power is turned back on. When it is turned back on, the electrical connection will not short to ground. Temporarily place tin tape over the hole.

Step 3: Zero out the manometer and make sure the units on the manometer are set to inches of water column ("WC). Check that the removed thermal limit switch isn’t going to be shorted out on any metal, since the power will need to be turned back. Step 4: Temporarily pull/turn off the outdoor electrical disconnect because the outdoor condenser does not necessarily need to be turned on during this test. Then turn the power on to the furnace. Set the thermostat to air conditioning mode and turn the temperature down. After the blower motor is up to speed and the static pressure is constant, record the measurement. In this example, the static pressure before the coil is 0.857” WC, (inches of water column) This is a very high static pressure for the supply side of the system.

Step 2: Connect the static pressure tip to the positive port of the digital water column manometer. Then insert the static pressure tip into the hole, through the tin tape, while keeping the point facing downward toward the blower motor.

Interlude Click:

Great Video from Craig A2L Refrigerants R-454B and R-32 Explained! Bottles, Changes, Rules, Tools!