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Goodman · Heat pump

09 Low 24 V control voltage

Medium severity Goodman/Amana ComfortNet ASZC/GSZC/DSZC

What the control is telling you

The control sees its 24 V supply below 18 VAC. The unit may still seem to run. Clears when the control voltage goes back above 21 VAC.

Applies to: Communicating 2-stage condensers and heat pumps with the PCBHR104 or PCBHR105 outdoor control (7-segment display): ASXC16/18, GSXC16/18, DSXC16/18, ASZC16/18, GSZC16/18, DSZC16/18

Likely causes

  • Overloaded transformer
  • Low line voltage
  • Fuse or wiring problem in the 24 V circuit

Test and repair steps

  1. Warning: Kill power to the outdoor unit before touching wiring, the compressor terminals or the control.
  2. Check the low voltage fuse.
  3. Measure 24 V at the control (R to C) with all loads on; reduce load or replace the transformer if it sags.
  4. Check line voltage feeding the transformer.

Models that show this code

24 models in Goodman/Amana ComfortNet ASZC/GSZC/DSZC

ASZC160241ASZC160361ASZC160421ASZC160481ASZC160601ASZC180241ASZC180361ASZC180481ASZC180601DSZC160241DSZC160361DSZC160481DSZC160601DSZC180361DSZC180481DSZC180601GSZC160241GSZC160361GSZC160481GSZC160601GSZC180241GSZC180361GSZC180481GSZC180601

Other codes on the same units

  • 05 Open circuit - compressor off over 4 hours
  • 06 Open start circuit
  • 07 Open run circuit
  • 08 No line voltage
  • A2 Outdoor air temperature sensor fault
  • A3 Outdoor coil temperature sensor fault
  • b0 Indoor blower not running when it should be
  • b9 Indoor airflow lower than requested

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Source: Goodman ComfortNet ASXC/GSXC/DSXC, ASZC/GSZC/DSZC, AVPTC/MBVC service manual, Unitary Diagnostic Codes PCBHR104 p.71-77 and PCBHR105 p.78-84. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.