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Grocery Refrigeration Talk #LIVE

September 6, 2019

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In this live episode we have a fun conversation talking with Nathan Orr and Kevin Compass about Grocery Refrigeration

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Compressor Ohm Mistakes w/ Bert

HVAC School – For Techs, By Techs

Compressor Ohm Mistakes w/ Bert

In this episode, Bryan and Bert dive into the often misunderstood world of compressor testing, focusing on common mistakes technicians make when using ohmmeters, compressor[...]

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35:15

Compressor Ohm Mistakes w/ Bert

byBryan Orr

In this episode, Bryan and Bert dive into the often misunderstood world of compressor testing, focusing on common mistakes technicians make when using ohmmeters, compressor testers, and megohm meters. The conversation highlights how diagnostic errors can lead to unnecessarily condemned compressors and wasted time and resources.

The hosts begin by discussing fundamental concepts like the difference between “open” and “short” conditions, emphasizing that a path doesn’t necessarily indicate a short circuit—it simply means there’s a low-resistance path. They explore how many technicians get confused when testing terminals, mistakenly thinking that normal winding-to-winding measurements indicate a problem. Through practical examples from their field experience, they illustrate why understanding normal readings is crucial before taking any measurement.

A significant portion of the discussion centers on proper testing techniques for scroll compressors, which often show different measurements to ground compared to other compressor types due to their design, with windings submerged in refrigerant and oil. Bryan and Bert explain why standard motor testers can lead to false diagnoses when they indicate “bad” at threshold levels like 20 megohms—a reading that would be normal for many functional scroll compressors. They recommend proper megohm meters calibrated to appropriate voltage levels for accurate testing.

Key Topics Covered:

The difference between “open” circuits and “shorts” and how to properly interpret ohm readings
Common mistakes when testing compressor terminals, especially misinterpreting normal winding-to-winding measurements
How to properly check for shorts to ground and the importance of clean connections
Why scroll compressors naturally show different resistance-to-ground readings due to their design with submerged windings
Problems with inexpensive compressor testers that give false “bad” readings on functional equipment
The “redneck test” for isolating a compressor to determine if it’s truly the source of breaker trips
The importance of understanding meter auto-ranging and correctly interpreting readings in ohms, kilohms, and megohms
Why a reading below 0.5 megohms to ground is the general threshold for concern with scroll compressors
Differences between megohm meters, high pot testers, and standard multimeters
The misconception that winding-to-winding shorts are common without corresponding shorts to ground

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