Form I-UDA, P/N 195673 Rev 13, Page
8. Controls and
Operation
8.1 Thermostat
Use either an optional thermostat available with the heater or a field-supplied 24-volt
thermostat. Install according to the thermostat manufacturer’s instructions, paying par
-
ticular attention to the requirements regarding the location of the thermostat.
Make sure that the heat anticipator setting on the thermostat is 0.6 amps (or in accor
-
dance with the amperage value noted on the wiring diagram of your heater).
Make thermostat connections at the terminal strip on the back of the heater. The strip
has four terminals, R, G, W1, and W2; refer to the wiring diagram.
IMPORTANT:
All units MUST be operated by a 4-volt thermostat.
Never use a line
voltage disconnect switch as a means of operating the heater. Operating Model Sizes
30-125 by means other than a 24-volt thermostat may result in the flame rollout switch
tripping.
Unit Mounted Thermostat, Option CM3
-
If the heater was ordered with Option CM3,
a kit for mounting the thermostat on the rear of the heater is shipped separately. Follow
the instructions in the option package to attach the bracket.
Select a snap-action thermostat when using the unit mounted thermostat bracket. Do
not use a mercury switch thermostat because the vibration may cause excessive unit
cycling. Be careful with the thermostat leads; shorting the thermostat wires to a metal
surface will cause the transformer to fail.
Sizes 30-125 are equipped with a temperature activated manually reset flame rollout
switch. The flame rollout switch is located at the top of the burner assembly. It is factory
set and is non-adjustable. If the setpoint is reached, the flame rollout acts to interrupt
the electric supply to the gas valve. If the flame rollout switch activates, identify and cor
-
rect the cause before resetting the switch. Refer to the Maintenance Section, Paragraph
10.2.10, for information on probable causes and instructions on resetting the flame
rollout switch. (For location, see
FIGURE 18
, page 30.)
DANGER: If the manual reset flame rollout switch activates,
identify and correct the cause before resetting the switch.
Never bypass the flame rollout switch; hazardous conditions
could result. See Hazard Intensity Levels, page .
7.5.3 Door Switch -
Model UDAS only
All sizes of Model UDAS heaters are equipped with a door switch which prevents the
heater from operating when the service door panel is open. The service panel of a
Model UDAS is equipped with a pliable gasket material that fully seals the door to pro
-
vide added protection from building air entering the combustion zone of the heater. (For
switch location, see
FIGURE 18
, page 30.)
7. Electrical
Supply and
Wiring (cont’d)
7.5 Electrical
Operating
Components
(cont’d)
The main operating gas valve is powered by the 24-volt control circuit through the ther
-
mostat 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 30.)
WARNING: The operating valve is the prime safety shutoff.
All gas supply lines must be free of dirt or scale before con-
necting the unit to ensure positive closure. See Hazard Lev-
els, page .
7.5.4 Gas Valve
7.5.5 Fan Motor
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 characteristics.
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 volt
-
age, the horsepower may be larger than the standard motor. Refer to the motor name
-
plate to verify horsepower.
7.5. Flame Rollout Switch - Sizes 30-15
only
7.5.6 Venter Motor
The venter motor is assembled to the venter wheel and operates to provide combustion
airflow. Operation is controlled by the ignition control module (circuit board); refer to
ignition system in Paragraph 8.3.
