If you’re a service tech and suspect the HVAC’s compressor is acting up, here’s a straightforward way to diagnose and figure out what’s happening:

Identifying a Faulty Compressor

You’ve got a problematic HVAC. Let’s see if the compressor is the issue:

  1. Power & Capacitor Test: Ensure the power level is where it should be. Use your multimeter to check if the capacitor is delivering the right energy kick.
  2. Winding Measurements:
    • For PSC compressors, measure resistance (ohms) across common, run, and start windings. The values from common-to-run plus common-to-start should match the run-to-start reading.
    • For three-phase types, resistance readings for all windings should be close.
  3. Ground Resistance Test: Measure resistance between compressor terminals and ground. Below one megaohm? That’s a sign of an electrical issue.
  4. Amp Check: Compare your compressor’s actual amp draw to the max rating on the unit label. If it’s higher, the compressor isn’t starting up right.

Why Did the Compressor Fail?

Now, let’s determine why the compressor might be having issues:

  1. Voltage & Winding Confirmation: Ensure the right voltage is getting to the compressor and that windings are within spec.
  2. Starting Point Check: Make sure the parts that help the compressor start up are in good working condition.
  3. Temperature Test: Check the temperature difference between the inlet and outlet of the compressor. Similar temps might mean something’s bypassing inside or there’s a mechanical problem.
  4. Phasing Test (For Three-Phase Units): Use a phase meter to check power phases. If you switch two power wires and the problem becomes evident, there could be a supply power issue.

In Conclusion

Thoroughly checking the compressor helps pinpoint the issue and decide if a replacement is needed. Doing this right keeps the HVAC system working well and your customers happy. After all, a detailed compressor checkup is key to a job well done.

TL;DR: When diagnosing HVAC issues, technicians should conduct a series of tests on the compressor, including checking power levels, resistance measurements, and temperature differences. These steps help identify if and why the compressor might be failing, ensuring the HVAC system remains efficient and customers are satisfied.