23 INVALID BLOWER AIRFLOW SELECTION - Indicates improper "A/C" or "CF" switch setting. The 042 and 14 units can deliver 1-1/2 to 3-1/2 tons A/C and 600 to 1400 CFM for continuous fan. The 060 and 20 unit can deliver 2 to 5 tons A/C and 800 to 2000 CFM for continuous fan. If code is flashing unit will default to closest allowable airflow. 24 SECONDARY VOLTAGE FUSE IS OPEN Check for: - Short circuit in secondary voltage (24V) wiring.