FAN MOTOR
The following procedure may be used for setting a fan control:
1. Allow the burner or burner assembly to operate for a normal running period.
2. Lower the thermostat setting so that the burner(s) will not operate during the fan control setting procedure.
3. Place a thermometer in the furnace plenum or bonnet or in one of the warm-air ducts near the furnace.
4. Set the fan adjustment lever and the fan differential adjustment (when used) to their lowest or coldest position so that the fan will run continuously.
5. Watch the thermometer until the temperature drops to about 5F° (3C) above the temperature normally maintained in the rooms being heated.
6. As soon as the temperature on the thermometer has reached the appropriate level (see step 5), slowly move the fan temperature adjustment lever up to a point where it will stop the fan.
When setting a fan according to the aforementioned procedure, the speed of the fan must be set so that the average temperature rise through the furnace is about 90F° (50C).
In some installations, a drafty condition may result from the location or types of warm-air outlets. This condition can be corrected by the following adjustments to the procedure described previously:
1. Place the thermometer in front of the return air grille in the room or space that is most difficult to heat.
2. When the air leaving the room begins to feel cool, slowly move the fan adjustment up until the fan just stops.