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The evaporator-fan OFF delay can also be modified. Once

the call for heating has ended, there is a 10-minute period
during which the modification can occur. If the limit switch
trips during this period, the evaporator-fan OFF delay will
increase by 15 seconds. A maximum of 9 trips can occur,
extending the evaporator-fan OFF delay to 180 seconds.

To restore the original default value, reset the power to

the unit.

TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting heating selector lever below room tem-
perature will temporarily shut unit off until space tempera-
ture falls below thermostat setting.

Safety Relief —

A soft solder joint at the suction service

Schrader port provides pressure relief under abnormal tem-
perature and pressure conditions (i.e., fire in building).

Ventilation (Continuous Fan) —

Set fan and sys-

tem selector switches at ON and OFF positions, respec-
tively. Evaporator fan operates continuously to provide
constant air circulation. When the evaporator-fan selector switch
is turned to the OFF position, there is a 30-second delay be-
fore the fan turns off.

Operating Sequence

COOLING, UNITS WITHOUT ECONOMIZER — When
thermostat calls for cooling, terminals G and Y1 are ener-
gized, and the indoor (evaporator) fan motor (IFM), com-
pressor, and outdoor (condenser) fan motor (OFM) start. The
OFM runs continuously while the unit is in cooling. When
the thermostat is satisfied, compressor contactor (C) is de-
energized and the compressor and OFM shut off. After a
30-second delay, the IFM shuts off. If the thermostat fan
selector switch is in the ON position, the evaporator motor
will run continuously.
HEATING, UNITS WITHOUT ECONOMIZER — When
the thermostat calls for heating, terminal W1 is energized.
To prevent thermostat short-cycling, the unit is locked into
the Heating mode for at least 1 minute when W1 is ener-
gized. The induced-draft motor is energized and the burner
ignition sequence begins. The indoor (evaporator) fan motor
(IFM) is energized 45 seconds after a flame is ignited. On
units equipped for two stages of heat, when additional heat
is needed, W2 is energized and the high-fire solenoid on
the main gas valve (MGV) is energized. When the thermo-
stat is satisfied and W1 is deenergized, the IFM stops after
a 45-second time-off delay.
COOLING, UNITS WITH VARISLIDE™ ECONOMIZER
— When the outdoor-air temperature is above the outdoor-
air thermostat (OAT) setting and the room thermostat calls
for cooling, compressor contactor is energized to start com-
pressor and the outdoor (condenser) fan motor (OFM). The
indoor (evaporator) fan motor (IFM) is energized and the
economizer damper moves to the minimum position. After
the thermostat is satisfied, there is a 30-second delay before
the evaporator fan turns off. The damper then moves to the
fully closed position. When using continuous fan, the damper
moves to the minimum position.

When the outdoor-air temperature is below the OAT set-

ting and the thermostat calls for cooling, the economizer damper
moves to the minimum position. If the supply-air tempera-
ture is above 57 F, the damper continue to open until it reaches
the fully open position or until the supply-air temperature
drops below 52 F.

When the supply-air temperature falls between 57 F and

52 F, the damper will remain at an intermediate open posi-
tion. If the supply-air temperature falls below 52 F, the damper
will modulate closed until it reaches the minimum position
or until the supply air temperature is above 52 F. When the
thermostat is satisfied, the damper moves to the fully closed
position when using AUTO. fan or to the minimum position
when using continuous fan.

If the outdoor air alone cannot satisfy the cooling require-

ments of the conditioned space, economizer cooling is in-
tegrated with mechanical cooling, providing, two stages of
cooling. Compressor and the condenser fan will be ener-
gized and the position of the economizer damper will be de-
termined by the supply-air temperature. When the second
stage of cooling is satisfied, the compressor and OFM will
be deenergized. The damper position will be determined by
the supply-air temperature. When the first stage of cooling is
satisfied, there is a 30-second delay before the evaporator
fan shuts off. The damper then moves to the fully closed po-
sition. When using a continuous fan, the damper moves to
the minimum position.

COOLING, UNITS WITH PARABLADE ECONOMIZER
− When the outdoor-air is above the enthalpy control setting
and the room thermostat calls for cooling, the compressor
contactor is energized to start the compressor and the out-
door (condenser) fan motor. The indoor (evaporator) fan mo-
tor is energized and the economizer damper moves to the
minimum position. After the room thermostat is satisfied, the
damper will spring return to the fully closed position.

When the outdoor-air is below the enthalpy control set-

ting and the thermostat calls for cooling, the economizer
outdoor-air damper is opened proportionally to maintain be-
tween 50 and 56 F at the mixed-air sensor. If outside air along
cannot satisfy the cooling requirements, economizer cooling
is integrated with mechanical cooling. When the room ther-
mostat is satisfied, the damper will spring return to the fully
closed position.
HEATING, UNITS WITH ECONOMIZER — When the ther-
mostat calls for heating, terminal W1 is energized. To pre-
vent thermostat short-cycling, the unit is locked into the Heating
mode for at least 1 minute when W1 is energized. The induced-
draft motor is energized and the burner ignition sequence
begins. The indoor (evaporator) fan motor (IFM) is ener-
gized 45 seconds after a flame is ignited and the damper moves
to the minimum position. On units equipped for two stages
of heat, when additional heat is needed, W2 energized
and the high-fire solenoid on the main gas valve (MGV) is
energized. When the thermostat is satisfied and W1 is de-
energized, the IFM stops after a 45-second time-off delay.
The economizer damper then moves to the fully closed po-
sition. When using continuous fan, the damper will remain
in the minimum position.