T066_F: Blower Cutback
Status
This is a non-critical fault experienced by the furnace. All operations (including thermostat calls) should continue abnormal with no perceivable difference in operation.
Description
The blower motor is operating at the highest rpm or torque that specifications allow but the application requires more torque or speed in order to get the desired airflow under the current static pressure conditions. The motor will continue to operate because internal software will prevent operation above the permitted range. However, a fault is sent to the furnace control (or I.F.C.) from the motor.
Note: This fault will not be displayed after the first three minutes of blower operation after power reset. Further, this fault will not be logged in the fault buffer or fault history after the first hour of operation and will only be logged into the fault buffer a maximum of one time. This code (66) indication is intended as a tool to notify the installer of inadequate airflow due to excessive static pressure in the duct of the system. The code is not intended to be a fault code. It is merely an operating indicator.
Expected Operation
All (including thermostat) operation should continue as normal. Blower operation may be slightly compromised but will continue.
Cause
1. The blower has hit the maximum speed or torque limit specified by the manufacturer because the static pressure is too high. At the end of the day, this is sort of a tattle tale that suggests the ductwork is too restrictive, it may be too small, the filter or evaporator coil may be dirty or too restrictive, too many registers are closed, or for whatever reason, the airflow is restricted.
Solution
The static pressure is too high because the duct work is improperly designed or is restricted for some other reason or the filter needs cleaning or replacing. Remove the obstruction or repair the duct so that static pressure does not exceed published values in the specification sheets or installation instructions for the furnace. Do your due dillegence to find the restriction in the air distribution system.
