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Safety Relief —
A soft solder joint at the suction service
Schrader port provides pressure relief under abnormal tempera-
ture and pressure conditions (i.e., fire in building). Use backup
wrench when tightening flare cap.
High Flow Valves —
Located on the compressor hot gas
and suction tubes are High Flow Valves. Large black plastic
caps distinguish these valves with O-rings located inside the
caps. These valves cannot be accessed for service in the field.
Ensure the plastic caps are in place and tight or the possibility
of refrigerant leakage could occur.
Ventilation (Continuous Fan) —
Set fan and system
selector switches at ON and OFF positions, respectively.
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 before the fan
turns off.
Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER — When
thermostat calls for cooling, terminals G and Y1 are energized,
and the indoor (evaporator) fan motor (IFM), compressor, and
outdoor (condenser) fan motor (OFM start. The OFM runs con-
tinuously while the unit is in cooling. When the thermostat is
satisfied, compressor contactor (C) is deenergized and the com-
pressor and OFM shut off. After a 30-second delay, the IFM
shuts off. If the thermostat fan selector switch is the ON posi-
tion, 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 energized. The
induced-draft motor is energized and the burner ignition se-
quence begins. The indoor (evaporator) fan motor (IFM) is en-
ergized 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 thermostat is satisfied and W1
is deenergized, the IFM stops after a 45-second time-off delay.
COOLING, UNITS WITH DURABLADE ECONO-
MIZER — 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
compressor 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 setting
and the thermostat calls for cooling, the economizer damper
moves to the minimum position. If the supply-air temperature
is above 57 F, the damper continues 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 to between 57 F and
52 F, the damper will remain at an intermediate open position.
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 will move to the fully closed position
when using AUTO. fan or to the minimum position when using
a continuous fan.
If the outdoor air alone cannot satisfy the cooling require-
ments of the conditioned space, economizer cooling is integrat-
ed with mechanical cooling, providing two stages of cooling.
Compressor and the condenser fan will be energized and the
position of the economizer damper will be determined 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 tempera-
ture. When the first stage of cooling is satisfied, there is a
30-second delay before the evaporator fan shuts off. The damp-
er then moves to the fully closed position. When using a con-
tinuous fan, the damper moves to the minimum position.
COOLING, UNITS WITH ECONOMI$ER — When the
outdoor-air temperature (OAT) is above the ECON SP set point
and the room thermostat calls for Stage 1 cooling (R to G +
Y1), the indoor (evaporator) fan motor (IFM) is energized and
the EconoMi$er damper modulates to minimum position. The
compressor contactor is energized to start the compressor and
outdoor (condenser) fan motor (OFM). After the thermostat is
satisfied, the damper modulates to the fully closed position
when the IFM is deenergized.
When the OAT is below the ECON SP setting and the room
thermostat calls for Stage 1 cooling (R to G + Y1), the
EconoMi$er modulates to the minimum position when the
IFM is energized. The EconoMi$er provides Stage 1 of cooling
by modulating the return and outdoor air dampers to maintain a
55 F supply air set point. If the supply-air temperature (SAT) is
greater than 57 F, the EconoMi$er modulates open, allowing a
greater amount of outdoor air to enter the unit. If the SAT drops
below 53 F, the outdoor air damper modulates closed to reduce
the amount of outdoor air. When the SAT is between 53 and 57
F, the EconoMi$er maintains its position.
If outdoor air alone cannot satisfy the cooling requirements
of the conditioned space, and the OAT is above the MECH
CLG LOCKOUT set point, the EconoMi$er integrates free
cooling with mechanical cooling. This is accomplished by the
strategies below.
NOTE: Compressor has a 2-minute Minimum On, Minimum
Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for Y2
(2-stage thermostat), the compressor and OFM are ener-
gized. The EconoMi$er damper is maintained at its cur-
rent position.
2. If Y1 is energized for more than 20 minutes, and Y2 is
not energized (whether or not a 2-stage thermostat is
used), the compressor and OFM are energized. The
EconoMi$er damper is maintained at its current position.
3. If Y1 is energized, and the compressor is already ener-
gized (see Step 2) and the room thermostat calls for Y2,
the compressor continues to operate.
4. If the compressor is energized and the thermostat is satis-
fied, the compressor, the OFM, and IFM are deenergized
and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
HEATING, UNITS WITH ECONOMI$ER — When the ther-
mostat 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 energized. The induced-
draft motor is energized and the burner ignition sequence be-
gins. The indoor (evaporator) fan motor (IFM) is energized
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 is energized and the high-
fire solenoid on the main gas valve (MGV) is energized. When
the thermostat is satisfied and W1 is deenergized, the IFM
stops after a 45-second time-off delay. The economizer damper
then moves to the fully closed position. When using continuous
fan, the damper will remain in the minimum position.