HVAC School - For Techs, By Techs
The Deep End with Roman Baugh: Live Call, Grounded Compressor, Mitsubishi Mini-Split
· Summarized
Key takeaways
- Electrical resistance readings are snapshots and can be affected by refrigerant migration or internal compressor issues.
- Intermittent resistance readings don't always mean a failed winding; system conditions like refrigerant in the compressor can skew results.
- Proper diagnosis involves understanding system history, behavior, and context, not just single measurements.
- Shutting down the system and observing whether it runs or attempts to start again can provide crucial clues about its condition.
- Listening to the system and asking why certain data points change helps in accurately diagnosing issues.
- Avoid jumping to conclusions based solely on initial resistance readings; consider mechanical issues and refrigerant migration.
Summary
Introduction and Sponsorship Highlights
The episode begins with Roman Baugh introducing the podcast sponsors, which include Refrigeration Technologies, Carrier, Navac, and TrueTechTools. Each sponsor is briefly described with the products or services they offer, emphasizing their support for the HVAC trade and the podcast's educational mission.
Live Call: Mitsubishi Mini-Split Compressor Troubleshooting
Roman shares a real-world troubleshooting call involving a Mitsubishi Mr. Slim mini-split with a grounded compressor. The call details diagnosing intermittent electrical resistance readings that initially suggested a compressor failure but were later contextualized as misleading due to refrigerant migration and other system behaviors. The conversation dives into the nuances of electrical testing, the importance of understanding refrigerant and compressor conditions, and how system history and behavior help guide accurate diagnosis.
Key Lessons from Troubleshooting and Diagnosis
Roman emphasizes that electrical readings at a single moment are just snapshots and shouldn't be the sole basis for diagnosing compressor failure. Variability in resistance readings can be caused by refrigerant migration and internal mechanical issues. The importance of methodical system shutdown, monitoring compressor behavior, and understanding refrigerant saturation temperatures are highlighted as critical steps. The call illustrates that diagnosing HVAC issues requires patience, asking why data changes, and understanding system theory rather than jumping to conclusions.
Conclusion and Final Insights
Roman concludes by reiterating that intermittent readings and system responses reveal much about internal conditions like refrigerant migration and mechanical faults. The overall message encourages technicians to listen carefully, follow the story the system tells, and avoid premature conclusions. The episode ends with a call for questions and links to industry resources.
Sponsors
- Refrigeration Technologies · Their Viper aerosol coil cleaner for condensers and evaporators is a fuming cleaner that you can spray directly into coils with a powerful pin spray. It has strong degreasing capabilities, is convenient to use with rinse or no-rinse options, and eliminates the need for bulky pump sprayers.
- Carrier · Carrier has been a long-term sponsor, providing a wide range of HVAC equipment from single-stage to high-efficiency models like the Green Speed Extreme. They support the podcast and the industry, and you can learn more or become a Carrier dealer at Carrier.com.
- Navac · Navac offers digital manifold gauges like the NX1 and NX4, supporting numerous refrigerants including A2L types. The NX1 supports 72 refrigerants, has a 600 psi working pressure, quarter-turn ball valves, and integrates with the NavX app and micron gauge for advanced diagnostics.
- TrueTechTools · TrueTechTools provides a vast catalog of over 90 brands of industry tools, backed by a team of experienced tradespeople for practical support. They support industry training and offer free resources, and you can get a discount by using the code GetSchooled at TrueTechTools.com.
Show notes
In this short podcast, Roman Baugh takes over with his new series, "The Deep End," where he shares tech support conversations. This time, Roman is on the other end of a live tech support call about a grounded compressor with an existing Mitsubishi mini-split (Mr. Slim heat pump). The unit in this case had an unclear service history due to the homeowner moving in recently.
In this issue, the compressor kicked on and kicked off immediately. After the technician in this scenario told tech support that he had no continuity from the compressor to ground, tech support asked him to check the resistance (which was 43 ohms from black to ground and 43 from white to ground). Tech support concluded that the compressor was grounded, and it needed to be replaced (along with the PCB). However, the resistance disappeared mid-call, and intermittent resistance readings don't always indicate a failed winding; it's worth noting that cool ambient temperatures that enable liquid refrigerant to migrate into the compressor could potentially skew electrical readings.
Roman recommended shutting the system down and trying to get the system to run. His rationale was that if the unit ran and didn't keep stopping, the system may have been overcharged or lacking a crankcase heater. However, that did not show any improvement in operation; the compressor rattled for about a second and shut off. A resistance test confirmed that the compressor was grounded, pointing to a mechanical issue with the compressor and not just a one-off instance of refrigerant migration. This type of failure can happen when there are repeated instances of liquid refrigerant in the crankcase over time.
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