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EC53 Outdoor ambient sensor (T4) fault

Medium severity Viessmann Vitocal 200-S DLCM(R/H)B multi-zone outdoorViessmann DLFSHB high wall indoor

What the control is telling you

Outdoor air sensor T4 open or shorted.

Applies to: DLCM(R/H)B multi-zone outdoor units with DLFSHBH high wall indoor units (Midea, Carrier, Viessmann)

Likely causes

  • Sensor plug loose
  • Bad T4 sensor
  • Bad outdoor PCB

Test and repair steps

  1. Safety kill power at the disconnect and wait for the inverter capacitors to discharge before touching boards or wiring.
  2. Check the sensor plug on the board and the wire for damage.
  3. Unplug the sensor and measure its resistance. T1-T4 sensors read about 10 kOhm at 77 F (25 C); the discharge sensor (T5/TP) about 54.9 kOhm at 77 F. Compare with the sensor resistance tables.
  4. Out of range or open/shorted replace the sensor. Sensor reads fine: replace the board it plugs into.

Models that show this code

12 models in Viessmann Vitocal 200-S DLCM(R/H)B multi-zone outdoor, Viessmann DLFSHB high wall indoor

DLCMHBH24CAKDLCMHBH30DAKDLCMHBH36DAKDLCMHBH48EAKDLCMRBH18BAKDLCMRBH36DAKDLCMRBH48EAKDLFSHBH09XAKDLFSHBH12XAJDLFSHBH12XAKDLFSHBH18XAKDLFSHBH24XAK

Other codes on the same units

  • EC07 Outdoor fan speed out of range
  • EC50 Outdoor temperature sensor fault
  • EC51 Outdoor EEPROM error
  • EC52 Condenser coil sensor (T3) fault
  • EC54 Discharge temperature sensor (TP/T5) fault
  • EC55 IPM temperature sensor fault
  • EC56 Indoor coil outlet sensor (T2B) fault
  • EC57 Refrigerant pipe sensor fault

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Source: DLCMRBH/DLCMHBH Multi-Zone Outdoor Service Manual (sold as Midea, Carrier and Viessmann Vitocal 200-S; Viessmann doc 6225551-03, 12/2024), Table 23 Outdoor Unit Error Display p.26; diagnosis p.40, 51; Carrier MS-DLFSHB-01 High Wall Ductless Service Manual (04/2021), Table 9 p.17. 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.