Reznor UDBS Unit Installation Manual - Manual (Page 27)

Form I-UDB, P/N 202658 R14, Page 27
8.0 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, if the thermostat has a heat anticipator setting, it is set to 0.6 amps (or
in accordance with the amperage value noted on the wiring diagram of your heater).
Connect the thermostat 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: This unit MUST be operated by a 24-volt thermostat. Never use a line
voltage disconnect switch as a means of operating the heater.
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.
Multiple Heater Control, Option CL31 and Option CL32 - If the heater was ordered
with a multiple heater control option, one thermostat can be used to control up to
six heaters. The option includes a 40VA transformer that replaces the standard trans-
former in the “controlling” unit and a relay assembly that attaches to the additional unit.
Option CL31 provides for control of two heaters. If control of more heaters is desired
(up to six total), Option CL32 which is the relay assembly only must be added to each
additional heater.
The option packages are shipped separately and include complete instructions on
installation and wiring.
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 22, page 35.)
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.
7.5.4 Gas Valve
7.5.5 Blower Motor Blower Model Sizes 30-125 are equipped with a direct drive motor. Blower Model
Sizes 150-400 have an adjustable belt drive motor from 1/4 to 5 HP.
Most blower motors are equipped with thermal overload protection of the automatic
reset type. If a motor is not equipped with thermal overload protection, the unit will be
equipped with a motor with an adjustable thermal overload starter. The adjustable set-
ting on the starter will be factory set to match the full load amp draw of the motor and
sealed. No change should be made to starter set unless the original motor is replaced.
Starters are manual reset. If an overload condition is experienced, the condition must
be corrected, and the starter must be manually reset.
After the installation is complete including all ductwork, the amp draw of the motor
should be checked with an amp meter to verify that the motor amp rating on the motor
nameplate is not being exceeded. Amps may be adjusted downward by reducing
blower speed or by increasing the duct system static pressure. The temperature rise
must be within the range specified on the unit rating plate
7.5.6 Venter Motor The venter motor is assembled to the venter wheel and operates to provide combus-
tion airflow. Operation is controlled by the ignition control module (circuit board); refer
to ignition system in Paragraph 8.3.