HVACopedia

Carrier · Air conditioner

16 Lost communication with user interface

Medium severity Carrier 2-stage 24ANB/25HNB

What the control is telling you

Amber STATUS light flashes 16: the outdoor board no longer hears the Infinity user interface.

Applies to: Carrier 24ANB1/24ANB7 two-stage AC

Likely causes

  • Loose or broken ABCD wiring
  • Wiring fault at indoor unit or UI
  • UI or indoor unit without power

Test and repair steps

  1. Check the A, B, C, D connections at the UI, indoor unit and outdoor board.
  2. Confirm 24 V between C and D at the outdoor unit.
  3. Look at the green COMM LED it should be on steady once messages are received.
  4. After 2 min without messages the board returns to standby.

Models that show this code

8 models in Carrier 2-stage 24ANB/25HNB

24ANB12424ANB13624ANB14824ANB16024ANB72424ANB73624ANB74824ANB760

Other codes on the same units

  • 25 Invalid model plug / inverter size
  • 31 High pressure switch open
  • 32 Low pressure trip
  • 45 Outdoor control board failure
  • 46 Brownout
  • 47 No 230 V at unit
  • 53 Outdoor air temperature sensor fault
  • 55 Outdoor coil temperature sensor fault

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

Source: Carrier Residential AC & HP Application Guideline and Service Manual 24-25-9SM (text export), Table 18 Troubleshooting. 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.