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D. Cooling, Units With EconoMi$er
When the Outdoor Air Temperature (OAT) is above the
ECON SP set point and the room thermostat calls for
Stage 1 cooling (R to G + Y1), the indoor-fan motor (IFM) is
energized and the EconoMi$er damper modulates to mini-
mum position. The compressor contactor and OFC are ener-
gized starting the compressor and outdoor-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 cool-
ing by modulating the return and outdoor-air dampers to
maintain a 55 F supply air set point. If the supply-air tem-
perature (SAT) is greater than 57 F, the EconoMi$er modu-
lates open, allowing a greater amount of outdoor air to enter
the unit. If the SAT drops below 53 F, the outdoor-air damper
modulates closed to reduce the amount of outdoor air. When
the SAT is between 53 and 57 F, the EconoMi$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$er integrates free
cooling with mechanical cooling. This is accomplished by the
strategies below.
NOTE: Compressors have a two-minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage thermostat), the compressor number 1
and OFM are energized. The position of the
EconoMi$er damper is maintained at its current
value.
2. If Y1 is energized for more then 20 minutes, and Y2 is
not energized (whether or not a 2-stage thermostat is
used), compressor no. 1 and OFM are energized. The
position of the EconoMi$er damper is maintained at
its current value.
3. If Y1 is energized, and compressor no. 1 is already
energized and the room thermostat calls for Y2,
compressor no. 1 continues to operate. If Y2 remains
energized for more than 20 minutes, compressor no. 2
is energized.
NOTE: Compressor no. 2 cannot be energized unless there is
a signal for Y2 from the space thermostat.
4. If compressor no. 2 is energized, and the Y2 signal
from the thermostat is satisfied, compressor no. 1 and
2 are deenergized. Re-asserting Y2 will start com-
pressor no. 1 and (after a 20-minute interstage delay)
compressor no. 2.
5. If compressor no. 1 is energized and the thermostat is
satisfied, compressor no. 1, the OFM, and IFM are
deenergized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
E. Heating, Units With Economizer (If Accessory Heater is
Installed)
When the room thermostat calls for heat through terminal
W1, the indoor-fan contactor outdoor fan contactor, C1, and
C2 are energized. On units equipped for 2 stages of heat,
when additional heat is needed, heater contactor is
energized through W2. The indoor-fan motor is energized,
and the economizer damper moves to the minimum position.
If the two-position damper is used, the outdoor-air damper
opens to the minimum position whenever the indoor fan
opens. When the thermostat is satisfied, the damper moves
to the fully closed position.
F. De fro st
When the temperature of the outdoor coil drops below 28 F
as sensed by the defrost thermostat (DFT2) and the defrost
timer is at the end of a timed period (adjustable at 30, 50, or
90 minutes), reversing valve solenoids (RVS1 and RVS2) are
energized and the OFC is deenergized. This switches the
position of the reversing valves and shuts off the outdoor
fans. The electric heaters (if installed) will be energized.
The unit continues to defrost until the coil temperature as
measured by DFT2 reaches 65 F, or the duration of defrost
cycle completes a 10-minute period.
During the defrost mode, if circuit 1 defrosts first, RVS1 will
oscillate between heating and cooling modes until the defrost
mode is complete.
At the end of the defrost cycle, the electric heaters (if in-
stalled) will be deenergized; the reversing valves switch and
the outdoor-fan motors will be energized. The unit will now
operate in the heating mode.
If the space thermostat is satisfied during a defrost cycle, the
unit will continue in the defrost mode until the time or tem-
perature constraints are satisfied.
SERVICE
I. CLEANING
Inspect unit interior at the beginning of each heating and
cooling season or more frequently as operating conditions
require.
A. Indoor Coil
1. Turn unit power off and tag disconnect. Remove filter
access panel and indoor coil access panel.
2. If economizer or accessory two-position damper is in-
stalled, remove economizer/two-position damper by
disconnecting economizer plug and removing mount-
ing screws (see Fig. 14, 15, or 22). Refer to Accessory
Economizer or Two-Position Damper Installation
Instructions for more details.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dish-
washer detergent in a pressurized spray canister.
Wash both sides of coil and flush with clean water.
For best results, backflush toward return-air section
to remove foreign material. Caution should be taken
as to not overflow the evaporator drain condensate
pan.
5. Flush condensate pan after completion.
6. Reinstall economizer/two-position damper and filters.
7. Reconnect wiring.
8. Replace access panels.
CAUTION: When servicing unit, shut off all elec-
trical power to unit and install lock out tag to avoid
shock hazard or injury from rotating parts.