FAN & LIMIT CONTROL
This thermally operated control has a probe to sense air temperature inside the appliance adjacent to the heat
exchanger. Fig. 3 shows the main parts of a Honeywell L4064 Fan & Limit Control. Refer to Fig. 4 for its
settings. For controls equipped with the Manual-Auto switch button constant fan operation can be achieved by
pushing it to the MAN position.
High Limit Setting: See Figs. 2, 3 and 4. This setting is factory set – DO NOT CHANGE
The high limit setting limits burner operation. When the air temperature inside the appliance reaches the set
high limit value, overheating of the furnace is prevented by cutting power to the burner. When the temperature
falls below the set high limit the burner power is restored.
Fan-On Setting: See Figs. 2, 3 and 4. This setting starts the air circulation blower when the burner has warmed
the furnace to the fan-on temperature
Fan-Off Setting: See Figs. 2, 3 and 4. This setting keeps the air circulation blower running until the temperature
of the heat exchanger drops to the fan-off temperature. This ensures the blower adequately cools the heat
exchanger before shutting off and keeps cool air from being circulated through the ductwork.
Fan differential (difference between the Fan On & Fan Off settings) should be at least 15
o
F (8
o
C).
FIG. 4. FAN AND LIMIT SETTINGS
FAN ON FAN OFF LIMIT*
NH3
125 90
200
LFR
110 90 200
* Do not change high limit setting
COMBUSTION AND VENTILATION AIR FOR CHIMNEYS & POWER VENTERS
Free air for combustion and ventilation must be permanently provided to the furnace room. Combustion
air refers to the total air requirements of the fuel-burning appliance. This includes air for the combustion
process and air to provide chimney draft (dilution air). Ventilation air provides free circulation of air in the
room where the appliance is located to keep ambient temperatures within safe limits under normal
conditions.
FIG. 2. TWO SPEED FAN & LIMIT CONTRL-L6064A FIG. 3. SINGLE SPEED FAN & LIMIT - L4064B
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