035-14527-000 REV A (599)
Form 650.77-N3U
16
Unitary Products Group
adjustments. Follow the thermostat manufacturer's instruc-
tions.
The 24-volt, 40 VA transformer is sized for the furnace com-
ponents only, and should not be connected to auxiliary
devices such as humidifiers, air cleaners, etc. The trans-
former may provide power for an air conditioning unit contac-
tor.
SAFETY CONTROLS
Blower Door Safety Switch:
This unit is equipped with an
electrical interlock switch mounted in the blower compart-
ment. This switch interrupts all power at the unit when the
panel covering the blower compartment is removed.
Electrical supply to the unit is dependent upon the panel that
covers the blower compartment being in place and properly
positioned.
Rollout Switch Controls:
These controls are mounted on
the burner assembly. If the temperature in the burner com-
partment exceeds its set point, the ignitor control and the gas
valve are de-energized. This is a manual reset control and
must be reset before operation can continue.
The operation of this control indicates a malfunction in the
combustion air blower or a blocked vent pipe connection.
Pressure Switch:
This furnace is supplied with two differen-
tial pressure switches which monitor the flow through the fur-
nace and venting system. This switch de-energizes the
ignition control module and the gas valve if any of the follow-
ing conditions are present:
1.
Blockage of internal flue gas passageways.
2.
Blockage of vent piping.
3.
Failure of combustion air blower/motor.
Limit Control:
The high temperature limit control is located
on the furnace vestibule panel just to the right and above the
gas valve. This is an automatic reset control and provides
over temperature protection due to reduced airflow, such as a
dirty filter.
Auxiliary Limit:
ControlsThese high temperature limit con-
trols are located in the blower compartment, one on each
side on upflow/horizontal unit. Downflow units have a single
limit mounted on the blower assembly. These are manual
reset controls and give high temperature protection when the
unit is applied in the horizontal position.
Control Circuit Fuse:
A 3 amp fuse is provided to protect
the 24 volt transformer from overload caused by control cir-
cuit wiring errors. This is an ATO 3, automotive type fuse and
is located in the unit wiring harness between the control
transformer and the furnace control.
START-UP AND ADJUSTMENTS
The initial start-up of the furnace requires the following addi-
tional procedures.
1.
When the gas supply is initially connected to the furnace,
the gas piping may be full of air. In order to purge this air,
it is recommended that the ground joint union be loos-
ened until the odor of gas is detected. When gas is
detected, immediately retighten the union and check for
leaks. Allow five minutes for any gas to dissipate before
continuing with the start-up procedure.
2.
All electrical connections made in the field and in the fac-
tory should be checked for proper tightness.
Blower and burner must never be operated without
the blower panel in place.
Main power supply to the unit must still be inter-
rupted at the main power disconnect switch before
any service or repair work is to be done to the unit.
Do not rely upon the interlock switch as a main
power disconnect.
