HVACopediaKeepRite · Air conditioner troubleshooting
Checking OAT and OCT thermistors - KeepRite C4A3/CXA6
What is going on
How to check the outdoor air and coil thermistors behind codes 53, 55 and 56.
Likely causes
- Failed thermistor
- Sensor moved from its factory location
- Loose OCT clamp
Check in this order
- Unplug the thermistor assembly from the board.
- Measure each thermistor and compare with the resistance curve (about 16,000 ohms at 60°F).
- Check the OAT is locked in its keyhole in the control box shelf.
- Check the OCT (C4A3 sizes 24 and 30) is fastened tightly on the liquid tube.
- Replace any sensor out of range. The board falls back to default operation if a sensor fails.
Applies to: KeepRite C4A3/CXA6 AC with outdoor control board
Take it to the job
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Source: KeepRite/ICP C4A3/H4A3/T4A3/CXA6 Installation Instructions 421 01 5103 05, Temperature Thermistors p.16, Fig. 17-18 p.14 and p.18. Written in our own words; check the manual for your exact model.
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.