FloAire FAV-M - Manual (Page 28)

28
Maxitrol 14
Amplifier
Air Flow Switch
High Temperature Limit
Air Flow Switch
There are both high and low airflow switches contained within one housing
measuring the pressure drop across the burner. This is to insure that there is
proper airflow (.15 in. w.c. to .95 in. w.c.) across the burner and proper
combustion at all times. Both switches are wired in series and have single pole
double throw (one common contact, one normally open contact, and one normally
closed contact) switches that are ‘switched’ by air pressure. There are two airflow
tubes in the heater, located near the burner and profile plate assembly (profile plates
surround the burner and control air into the burner section). In the case of clogged
filters, blocked intake, excessive duct static pressure, or a broken belt, the correct
burner differential pressure may not be achieved, not allowing the low airflow switch
to close. The high airflow switch protects against profile plate failures that cause
excessive airflow through the burner. In the event that the pressure drop across the
burner is not in the range of the airflow switch, gas flow to the burner is stopped by the Flame Safety
Control.
Unit Type Air Flow
Switch
Part Number
Low
Setting
In. W.C.
High
Setting
In. W.C.
Target Pressure
Drop In. W.C.
Natural Gas
Target Pressure
Drop In. W.C.
Propane Gas
80/20 DDP-106-256 0.15” 0.95” 0.45-0.65” 0.45-0.65”
Modulating Gas System
The second system, the Maxitrol modulating gas system, consists of a
temperature selector dial, a discharge air sensor, an amplifier, and a modulating
gas valve. The two types of Maxitrol systems used are the Maxitrol 14 series or
the Maxitrol 44 series. The Maxitrol 14 utilizes a discharge air sensor and
modulates the Maxitrol gas valve to provide discharge air to match the selected
temperature on the temperature selector. The Maxitrol 44 utilizes a room
temperature sensor to control room temperature as well as a discharge air
sensor in order to control the discharge air temperature. The modulating gas
valve controls the amount of gas flow to the burner based on the temperature rise
needed. When the modulating gas valve is all the way open and achieving the
maximum BTUs and temperature rise of the unit, it is called “high fire”.
High Temperature Limit
One of the safety device is the high temperature limit switch. This switch is a
mechanical thermostat that measures the temperature inside the unit downstream of the
burner. If the factory-set temperature is exceeded, it will signal the FSC to turn off the
burner. This requires a manual reset of the high temperature limit. This insures that the
discharge does not exceed 185°F.
Electric Cabinet Heater
On units shipped with an optional electric cabinet heater, ensure that the heater is wired to a separate
120V, 15 amp input, the thermostat sensing bulb is mounted correctly in the control vestibule where the
heater is located, and the thermostat set to 0 Degrees Fahrenheit.