Measuring Inrush Amps

In a collaboration with TruTech Tools, Bryan shows us a way of measuring inrush amps on a system using the Testo 770-3. He also explains what hard start kits are and what they do. For safety reasons, it's best to disconnect power before taking the electrical panel off. It's also a good idea to disconnect the wires from a hard start kit until later on, as those can make a large difference in your inrush amp measurements. Bryan takes the Testo 770-3 and turns the dial to measure amps. He also presses the "inrush" button; to confirm that your meter is reading inrush amps, check for "INRUSH" on the display. Then, he checks the inrush amps on the compressor. After turning the power back on, Bryan reads his meter and sees that it picked up 132.2 inrush amps. The run amps are only 20.6. With the hard start kit connected, the inrush amps drop to 82.1. That's because a hard start kit helps a compressor start when it's in a locked rotor state. The hard start kit is very fast and forceful, which shortens the amount of time that locked rotor amperage is drawn. So, the inrush amps don't actually "drop;" they're just greatly shortened because they greatly increase the speed at which a motor goes from a locked rotor condition to a fully rotating condition. Find more quality Testo products at trutechtools.com. Read all the tech tips, take the quizzes and find our handy calculators at https://www.hvacrschool.com/