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882108-YIM-B-1012
Johnson Controls Unitary Products 83
GAS FURNACE SAFETY FEATURES
COMBUSTION AIR PROVING
Combustion air proving is provided by a pressure switch. As
the motor approaches full speed, this switch closes before
any other circuit or gas component can be energized.
ROLLOUT
Rollout protection is provided by a switch mounted on the
heat shield of each furnace module. The switch senses any
flame or excessive heat in the burner compartment. When
the switch opens, the furnace module is immediately locked
out until there is a break in power to the specific furnace mod-
ule and the manual itch is reset. Note that only the module
with the open rollout switch will be locked out, the remaining
modules will continue to operate although all should be
inspected.
A trip of the rollout switch likely indicates a flue restriction, an
opening in the flue passageway, defective pressure switch or
a loose combustion blower wheel. Corrective action should
be taken accordingly.
MAINTENANCE
NORMAL MAINTENANCE
Periodic maintenance normally consists of changing or clean-
ing filters and (under some conditions) cleaning the main
burners.
FILTERS
Inspect once a month. Replace disposable or clean perma-
nent type as necessary. The dimensional size of the replace-
ment filter must be the same as the replaced filter (Refer to
Table 15).
MOTORS
Outdoor fan motors are permanently lubricated and require
no maintenance. Lubrication, if desired, is to be performed by
a qualified service agency.
Ventor motors are factory lubricated for an estimated 10-year
life.
Indoor Fan Motors - The indoor blower motor features ball-
bearings that do not require periodic lubrication. Periodic
lubrication of the motor bearings can extend the life but is
optional.
To go to bypass mode, the bypass VFD as installed in this
unit must be switched by hand on the front of the bypass
enclosure in the fan cabinet of the rooftop unit. It does not
automatically go to bypass mode if the drive fails.
The switches on the front of the bypass box control its run
mode. For normal running:
• The ON/OFF rotary power switch must be in the ON
position.
• The BYPASS/OFF/DRIVE switch S1 should be in the
DRIVE position.
• The HAND/STOP/AUTO switch S2 should be in the
AUTO position, so that the unit control will properly run
the fan and control the speed.
• The TEST/NORMAL switch S3 should be in the NOR-
MAL position.
Prior to any of the following maintenance proce-
dures, shut off all power to the unit. Failure to do
so could cause personal injury.
Label all wires prior to disconnection when servic-
ing controls. Wiring errors can cause improper and
dangerous operation. Verify proper operation after
servicing.
Damage can occur if the bearings are over lubri-
cated. Use grease sparingly.
If the unit is operated with the manual bypass
switch in the LINE (BYPASS) position and there
are VAV boxes present, the boxes must be driven
to the full-open position using a customer-supplied
power source to prevent over-pressuring the
ductwork.
Perform all maintenance operations on the blower
motor with power disconnected from the unit. Do
not attempt to lubricate bearings with the unit in
operation.