90 Communication fault

What the control is telling you

Listed as 'Communication Fault' but the manual's description says the ICC has detected an internal fault and should be replaced - manual inconsistency.

Applies to: (-)PRL-JEC 2-stage 16 SEER heat pumps: RPRL/UPRL-024JEC, -036JEC, -048JEC, -060JEC

Likely causes

• Communication wiring problem (1/2 data wires)
• ICC internal fault

Test and repair steps

1. Check data wires 1 and 2, R and C at the thermostat, indoor and outdoor units - reversed comm wires keep the green comm LED (D52) on solid.
2. Check term/bus dip switches on the ICC and air handler (term switches ON).
3. Never use phone cord or connect the system to a phone line.
4. If wiring is correct, replace the ICC (move the memory card to the new board).

Settings for these units

Outdoor unit clearances · Rheem/Ruud PRL-JEC heat pump (Comfort Control2 ICC)

Do not reduce the 60 in. discharge or 24 in. service clearances.

Inlet clearances under 6 in. reduce capacity and efficiency.

Models that show this code

4 models in Rheem/Ruud PRL-JEC heat pump (Comfort Control2 ICC)

Other codes on the same units

• 30 ICC fuse open
• 80 Low airflow
• 83 Condenser coil temperature sensor fault
• 84 Outdoor ambient temperature sensor fault
• 93 Internal control fault
• d1 No shared data
• d3 Airflow CFM mismatch
• d4 Memory card invalid for device