The chart above is from a Carrier heat pump, and it lists some common accessories. I have heard this common pressure switch (last on the list) called a low-pressure switch (because it opens on fall in pressure) and a high-pressure switch (because it's in the liquid line), but RARELY do I hear it called its […]

Testo 760 Category IV Multimeter I was standing at a booth at the HVAC Excellence Educators conference, and an instructor walks up, grabs a meter, and asks me, “What's the difference between a category 3 and a category 4 meter?” Well, I really wasn't sure, but I knew that the category 4 meter is rated […]

When you work on a heat pump system and want to test defrost, you can follow many different test procedures to test the board and sensors. Most involve “forcing” a defrost by shorting out pins on the board or advancing the time of the defrost initiation and installing a factory-provided pin jumper. Lots of pins […]