35
When the second stage of cooling is satisfied, the compres-
sor and condenser-fan motors will be deenergized. The damper
position will be determined by the supply-air temperature.
When the first stage of cooling is satisfied and the indoor
(evaporator) fan motor is deenergized, the damper will move to
fully closed position.
COOLING, UNIT 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 minimum position. The
compressor contactor and OFC are energized starting the com-
pressor and outdoor-fan motors (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$er integrates free
cooling with mechanical cooling. This is accomplished by the
strategies below.
NOTE: Compressors have a two-minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage thermostat), the compressor number 1 and
OFM are energized. The position of the EconoMi$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$er damper is maintained at its
current value.
3. If Y1 is energized, and compressor no. 1 is already
energized and the room thermostat calls for Y2,
compressor no. 1 continues to operate. If Y2 remains
energized for more than 20 minutes, compressor no. 2
is energized.
NOTE: Compressor no. 2 cannot be energized unless there is a
signal for Y2 from the space thermostat.
4. If compressor no. 2 is energized, and the Y2 signal
from the thermostat is satisfied, compressor no. 1 and
2 are deenergized. If the thermostat reenergizes Y2
will start compressor no. 1 and (after a 20-minute
interstage delay) compressor no. 2.
5. If compressor no. 1 is energized and the thermostat is
satisfied, compressor no. 1, the OFM, and IFM are
deenergized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
HEATING, UNITS WITH DURABLADE ECONOMIZER
OR ECONOMI$ER — When the room thermostat calls for
heat, the heating controls are energized as described in the roof-
top unit Installation, Start-Up and Service Instructions.The IFM
is energized and the Durablade economizer or EconoMi$er
damper modulates to the minimum position. When the thermo-
stat is satisfied, the damper modulates closed.
SERVICE
Cleaning —
Inspect unit interior and exterior at the begin-
ning of each heating and cooling season or more frequently as
operating conditions require.
EVAPORATOR COIL
1. Turn unit power off, tag disconnect. Remove evaporator
coil access panel.
2. If economizer is installed, remove economizer by discon-
necting Molex plug and removing economizer mounting
screws. Refer to Accessory Economizer Installation In-
structions or Optional Economizer sections, on pages 12
and 15 for more details.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dishwasher
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.
5. Flush condensate pan after completion.
6. Reinstall economizer and filters.
7. Reconnect economizer wiring.
8. Replace access panels.
CONDENSER COIL — Inspect coil monthly. Clean con-
denser coil annually, or as required by location and outdoor-air
conditions.
One-Row Coil — Wash coil with commercial coil cleaner.
Clean the outer surfaces with a stiff brush in the normal man-
ner. It is not necessary to remove top panel.
Two-Row Coils — Clean coils as follows:
1. Turn off unit power, tag disconnect.
2. Remove top panel screws on condenser end of unit.
3. Remove condenser coil corner post. See Fig. 46. To hold
top panel open, place coil corner post between top panel
and center post. See Fig. 47.
4. Remove screws securing coil to center post.
5. Remove fastener holding coil sections together at return
end of condenser coil. Carefully separate the outer coil
section 3 to 4 in. from the inner coil section. See Fig. 48.
6. Use a water hose or other suitable equipment to flush
down between the 2 coil sections to remove dirt and de-
bris. Clean the outer surfaces with a stiff brush in the nor-
mal manner.
7. Secure inner and outer coil rows together with fastener re-
moved in Step 5.
8. Reposition the outer coil section and remove the coil cor-
ner post between the top panel and center post. Reinstall
the coil corner post and replace all screws.
CONDENSATE DRAIN — Check and clean each year at
start of cooling season. In winter, keep drain dry or protect
against freeze-up.
FILTERS — Clean or replace at start of each heating and cool-
ing season, or more often if operating conditions require it. Re-
placement filters must be same dimensions as original filters.
When servicing unit, shut off all electrical power to unit to
avoid shock hazard or injury from rotating parts.
Summary of Contents for 50TFF008-014
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