Service Manual

SYSTEM OPERATION

22. Motor Parameters. This condition occurs if the motor

does not receive all the information is requires to oper-

ate or an event occurs that prevents the motor from run-

ning, or the motor fails to start for (40) consecutive at-

tempts. The diagnostic error code for the this condition

is b7. Probable causes are intermittent wiring connec-

tion between the control and motor, an error with the

furnace control, or any of the conditions described in

19, 20, or 21 above.

23. Low Indoor Airflow. This condition occurs if the in-

door airflow falls below a calculated minimum value. The

minimum airflow value is calculated from factors defined

in the shared data set. If the airflow falls below the

calculated minimum, the furnace will continue to oper-

ate with the reduce airflow. If the furnace was operating

at high stage, it will stage back to low in an effort to

remedy the condition. The furnace will halt operation if

the airflow falls to 0 CFM.

The diagnostic error code for the this condition is b9.

Probable causes are blocked/clogged filters, blocked

or restrictive ductwork, or undersized ductwork.