Compressor Ohm Mistakes w/ Bert

Key takeaways

Understanding the difference between 'open' and 'short' circuits is fundamental for accurate compressor testing.
Common mistakes made by technicians include misinterpreting normal winding-to-winding readings and using non-ideal testing equipment.
Scroll compressors have unique characteristics that affect resistance measurements; using a standard motor tester may lead to falsely labeling a functioning unit as 'bad'.
Isolation tests are critical for determining if a compressor is the source of failure before condemning it.
Having solid foundational knowledge allows technicians to troubleshoot effectively and minimize errors in diagnosis.

Summary

Understanding Compressor Testing

In this episode, Bryan and Bert dive deep into the complexities of compressor testing, particularly focusing on the common mistakes technicians make when it comes to using ohmmeters, compressor testers, and megohm meters. A significant part of the discussion centers around fundamentally understanding the difference between 'open' circuits and 'short' circuits. They emphasize that seeing a low-resistance path does not necessarily indicate a short circuit but rather a pathway exists. This misunderstanding often leads technicians to mistakenly condemn working compressors.

Common Mistakes in Testing and Measurement

Bryan and Bert discuss the common pitfalls technicians encounter when testing compressor terminals. They highlight that technicians frequently misinterpret normal winding-to-winding measurements, leading them to arrive at inaccurate diagnoses. The duo explains the importance of clean connections and the correct testing techniques to ensure precise readings. Understanding normal readings and how compressor design affects resistance-to-ground readings for different types of compressors is crucial for accurate testing.

Scroll Compressors and Unique Challenges

A significant topic covered is how scroll compressors differ in design from traditional compressors, leading to varied measurements of resistance to ground. Bryan and Bert clarify that the windings submerged in refrigerant make the testing unique. Regular motor testers that indicate 'bad' at high resistance levels (like 20 megohms) can lead to erroneous condemnations of functional scroll compressors.

Testing Techniques and Best Practices

Bryan and Bert offer practical advice on proper testing techniques, emphasizing the need to isolate a compressor from the system to accurately diagnose whether it’s the source of breaker trips. They share their 'redneck test' method for isolating faults and stress the importance of confirming measurements with good connections while being aware of auto-ranging meters. They highlight the magic threshold for concern on resistance readings, particularly for scroll compressors.

The Importance of Fundamental Knowledge

The episode wraps up with a discussion on the fundamental knowledge every technician should have—understanding normal operating conditions and knowing when to trust tools. Bryan and Bert encourage technicians to use their knowledge to double-check findings rather than relying solely on tools, ensuring they don't misdiagnose compressor issues.

Show notes

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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