The control switches the motor to {HEAD ~ a speed} substantially slower than {TAIL ~ the operating condition speed} to provide continuing air circulation until the thermostat again calls for thermal operation 
substantially slower than
The control switches the motor to { HEAD ~ a speed } substantially slower than { TAIL ~ the operating condition speed } to provide continuing air circulation until the thermostat again calls for thermal operation
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH