If there is one tool that is absolutely important for every HVAC technician to own it is a multimeter.
A multimeter is a special tool that fits in the palm of your hand.
A multimeter usually has a numerical display and a graph to measure all of the values. Digital multimeters are low-cost and they can be purchased at any hardware store. A multimeter can measure voltage, current, and also resistance. I bought a new multimeter a couple of weeks ago and I used the machine every single day on the job. Last week, I was working on an HVAC installation job and I was using the multimeter. I turned it on but I did not get any power at all. I hit the side of the machine, but it still didn’t power on. I put a couple of new batteries in the back of the digital machine but that did not work either. I use that tool every day for weeks and weeks and I could not believe that it suddenly stopped working without a single problem. I had to go to the shop and borrow another tool so I could finish the HVAC installation job. It took an hour to drive back to the shop and then back to the residence. I spent eight hours working on that HVAC installation job and I didn’t have my favorite tool to get everything done. I took the multimeter back to the hardware store as soon as my work day was done. The guy exchanged the machine without asking a lot of questions, so it might have been a manufacturer defect.