Thomas & Betts UDAP - Manual (Page 22)

Form RZ-NA I-UDA, P/N 195673 Rev 5, Page 22
The main operating gas valve is powered by the 24-volt control circuit through the
thermostat and safety controls. The main control valve is of the diaphragm type
providing regulated gas flow preset at the factory. (For location, see FIGURE 18,
page 31.)
WARNING: The operating valve is the prime safety shutoff. All
gas supply lines must be free of dirt or scale before connecting
the unit to ensure positive closure. See Hazard Levels, page 2.
The fan motor is equipped with thermal overload protection of the automatic reset
type. Should the motor refuse to run, it may be because of improper current char-
acteristics. Make certain that the correct voltage is available at the motor.
NOTE: If the unit is equipped with an optional totally enclosed motor or optional
voltage, the horsepower may be larger than the standard motor. Refer to the motor
nameplate to verify horsepower.
21. Gas Valve
20. Ignition
System
(cont’d)
22. Fan Motor
If the gas valve was sensed as closed when it should be open, and has not de-
energized after the venter motor was shutoff for 15 seconds, then the venter motor
is re-energized to vent the unburned gas.
Soft Lockout - The control shall not initiate a call for heat or call for continuous
fan while in lockout. The control will still respond to an open limit and undesired
flame. Lockout shall automatically reset after one hour. Lockout may be manually
reset by removing power from the control for more than one second or removing
the thermostat call for heat for more than one and less than 20 seconds.
Hard Lockout - If the control detects a fault on the control board, the status LED
will be de-energized, and the control will lockout as long as the fault remains. A
hard lockout will automatically reset if the hardware fault clears.
Power Interruption - During a momentary power interruption or at voltage levels
below the minimum operating voltage (line voltage or low voltage) the system will
self-recover without lockout when voltage returns to the operating range.
Power interruptions of less than 80mS shall not cause the control to change operat-
ing states. Power interruptions greater than 80mS may cause the control to inter-
rupt the current operating cycle and re-start.
Lockout
Fault Modes
(cont’d)