What should the delta T (ΔT) be? What do you mean!? 20 degrees, of course! We are referring to the air temperature drop across an air handling unit or evaporator coil in cooling mode. Actually, depending on who you ask, the answer will range between 18-22 degrees Fahrenheit. Heck, I’ve heard some insist that […]

There are three reasons why I don't like infrared thermometers for many HVAC tasks. #1 – The laser can be misleading The laser dot is just a point of reference, not an exact point where it is reading. Often the thermometer will read lower, higher, or over a MUCH wider area. Unless you are right […]

On an energized, intact circuit, you will read voltage across an OPEN switch when testing with a voltmeter. However, you probably won't read significant voltage across a CLOSED switch. Both sides of a closed switch are electrically identical (or at least very close). Therefore, there should be no movement of electrons between the leads of […]