seconds after the fan motors.
the compressor and fan motors operate
continuously in this mode,
action of the temperature selector
switch causes refrigerant to bypass the
evaporator coil and stop cooling when
the desired temperature setting of the
temperature selector switch is satis-
Ventilation air will be drawn in-
to the unit if the vent damper door is
(4) Low Heat.
In the low heat
mode, the evaporator fan motor operates
continuously and three of the six heater
elements are activated.
The three heat-
er elements cycle on and off under ther-
mostatic control of the temperature se-
This mode will produce
half of the units heating capability.
Ventilation air will be drawn into the
unit if the vent damper door is open.
(5) High Heat.
In the high heat
mode, the evaporator fan motor operates
continuously and all six of the heater
elements are activated, but only three
of the heater elements will cycle on and
off under thermostatic control of the
temperature selector switch.
will produce maximum heating capability
of the unit.
Ventilation air will be
drawn into the unit if the vent damper
door is open.
Evaporator Fan Speed Switch.
evaporator fan speed switch has two po-
sitions, low and high.
tions are manually selected to control
the evaporator fan speed in all operat-
Normally the low speed
should be selected as it is quieter and
requires less electrical power; however,
the high speed position has three ad-
vantages over low which may dictate
(1) Maximum cooling capacity can
only be achieved in high.
(2) The increased flow of evapora-
tor air improves air distribution in the
(3) Twice as much ventilation air
is drawn into the unit in high.
Vent Adjusting Knob.
adjusting knob controls the flow of ven-
tilation air into the unit.
The knob is
connected by the damper cable to a damp-
er located in the vent duct.
controls the flow of ventilation air by
adjusting the position of the damper
from full closed to full open.
the knob to the right closes the damper,
turning the knob to the left opens the
The force that draws ventila-
tion air into the unit is the small
pressure difference between the ambient
and the evaporator fan.
This is the
same small pressure difference that
exists between the conditioned space and
the evaporator fan; the pressure differ-
ence that draws return air through the
inlet louver and the return air filter.
When ventilation air enters the condi-
tioned space a like flow of air must ex-
haust from the space to prevent a pres-
Cracks in the space may
be sufficient; but if a large flow of
ventilation air is desired, some posi-
tive means of air exhaust should be pro-
The inlet louver
is finger-adjustable from full open to
Normally the louver shut-
ter tab adjustment is kept at 45° posi-
tion, which is essentially the same as a
full open inlet louver.
If the inlet
louver is closed, return air will still
manage to flow through it; but at a re-
duced rate with high pressure drop. The
increase in pressure drop will cause ad-
ditional ventilation air to be drawn in-
to the unit.
The vent mode of oper-
ation is normally the only mode where
closing the inlet louver (to create in-
creased ventilation airflow) would be
considered a real advantage.
ficient ventilation air flow for other
modes of operation can be achieved with
the inlet louver open and the damper
The return air filter is attached
to the back side of the inlet louver. A
dirty filter can easily be observed by
looking through the inlet louver blades.
Since maximum cooling capability of the
unit is obtained with maximum evapora-
tor air flow, a closed inlet louver or a
dirty air filter will decrease cooling
capacity, and may cause ice to form on
the evaporator coil.
The outlet louver
is finger-adjustable in both horizontal
and vertical planes.
This adjustment on
an individual blade basis allows maximum
control over the direction of outlet
The best distribution pattern for
outlet air is left to the operators
judgment; but blades should not be ad-
justed beyond 45°, as evaporator air
flow will be impeded.
er louvers, located on the rear of the