RT-SVX075C-EN
69
Note: Single zone VAV is designed to be used with a zone
sensor. If a unit is configured for Single zone VAV
operation but is connected to a thermostat, the
control will revert to multi-speed (2-speed) indoor
fan control and staged compressor control. This
drastically reduces the energy savings available with
this design.
Air Filters
Filters are to be used with this unit. Units ship from the
factory with filters installed.
Figure 77. Gas unit overview
SUPPLY AIR
RETURN AIR
PRESSURE SWITCH
GAS VALVE COMPRESSORAIR FILTERS
It is very important to keep the central duct system air filters
clean. Inspect them at least once each month when the
system is in constant operation. (In new homes, check the
filters every week for the first four weeks.) See the following
table for the required filter size(s).
If the unit has disposable type filters, replace them with
new filters of the same type and size. Do not attempt to
clean disposable filters.
Permanent type filters can be cleaned by washing them
with a mild detergent and water. Confirm the filters are
thoroughly dry before reinstalling them in the unit (or duct
system).
It may be necessary to replace permanent filters annually if
washing fails to clean the filter. Use the same type and size
as originally installed.
Table 18. Recommended standard filters
Tons
Unit Model
Number
Qty
Filter Size
(L x W x D)
6
YHJ072***(0,A,B)(L,M,H)
2 18 x 24 x 2
3 24 x 16 x 2
7.5
YHJ090***(0,A,B)(L,M,H)
2 18 x 24 x 2
3 24 x 16 x 2
8.5
YHJ102***(0,A,B)(L,M,H)
2 18 x 24 x 2
3 24 x 16 x 2
10
YHJ120***(0,A,B)(L,M,H)
2 18 x 24 x 2
3 24 x 16 x 2
12.5
YHJ150***(0,A,B)(L,M,H)
3 18 x 18 x 2
3 24 x 18 x 2
15
YHJ180***(0,A,B)(L,M,H)
8 20 x 24 x 2
17.5
YHJ210***(0,A,B)(L,M,H)
8 20 x 24 x 2
Table 18. Recommended standard filters (continued)
Tons
Unit Model
Number
Qty
Filter Size
(L x W x D)
20
YHJ240***(0,A,B)(L,M,H)
8 20 x 24 x 2
25
YHJ300***(0,A,B)(L,M,H)
8 20 x 24 x 2
Heating System
Heating Cycle Operation
The unit heating system is a solid-state electronic ignition
control that lights the furnace burners each time the
thermostat calls for heat. At the end of each heating cycle
the furnace burners are extinguished. This type of system
is called Direct Spark Ignition (DSI).
A normal heating cycle begins when the air temperature
drops below the thermostat setting. The thermostat then
energizes the heating electrical circuit that starts and
controls the furnace burners. Shortly after the burners
ignite the indoor fan starts and circulates warm air through
the conditioned space.
When the air temperature rises to the thermostat setting
the thermostat deenergizes the heating electrical circuit,
which in turn extinguishes the burners. The indoor fan
continues to circulate warm air until most of the heat is
removed from the unit's combustion chamber.
Safety Controls
• The unit is equipped with an automatic reset safety limit
control to prevent overheating. When the control
opens, it shuts down the heating electrical circuit until
the unit cools down sufficiently. Inadequate airflow (i.e.,
caused by dirty filters or defective fan motor) may
cause the unit to cycle on and off as the limit trips and
automatically resets. If the unit is cycling on its limit
control, immediately contact a service person for
instructions.
• If flames from the burner are not properly drawn into
the heat exchanger, a flame rollout protection control
will open causing the furnace to shut off. The cause
must be investigated by a qualified service person.
• If installed, the condensate overflow switch will shut
down the unit before a drain pan overflow occurs.
Heating System Start-Up
Because the unit has an automatic ignition system, it is
easy to start the heating cycle at the beginning of the
heating season. In order for the unit to operate properly
and safely, the furnace needs air for both combustion and
ventilation. Verify all air openings are unobstructed and
there is adequate clearance around the unit to provide
good airflow.
Gas Heat Operation and Maintenance
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