36
If the outdoor air alone cannot satisfy the cooling require-
ments of the conditioned space, economizer cooling is integrat-
ed with mechanical cooling, providing second-stage cooling.
Compressor no. 1 and the condenser fan will be energized and
the position of the economizer damper will be determined by
the supply-air temperature. Compressor no. 2 is locked out.
When the second stage of cooling is satisfied, the compres-
sor and OFM will be deenergized. The damper position will be
determined by the supply-air temperature.
After a 30-second delay, the IFM shuts off. If the thermostat
fan selector switch is in the ON position, the IFM will run
continuously.
COOLING UNITS WITH ECONOMI$ER — When the
OAT is above the ECON SP set point and the room thermostat
calls for Stage 1 cooling (R to G + Y1), the indoor fan motor
(IFM) is energized and the EconoMi$er damper modulates to
minimum position. The compressor contactor is energized to
start 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 cooling
by modulating the return and outdoor air dampers to maintain a
13 C (55 F) supply air set point. If the supply-air temperature
(SAT) is greater than 14 C (57 F), the EconoMi$er modulates
open, allowing a greater amount of outdoor air to enter the unit.
If the SAT drops below 12 C (53 F), the outdoor air damper
modulates closed to reduce the amount of outdoor air. When
the SAT is between 12 C (53 F) and 14 C (57 F), the
EconoMi$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$er integrates free
cooling with mechanical cooling. This is accomplished by the
strategies below.
NOTE: Compressors have a two-minute Minimum On, Mini-
mum Off, and interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for Y2
(2-stage thermostat), the compressor and OFM are ener-
gized. The position of the EconoMi$er damper is main-
tained at its current value.
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 posi-
tion of the EconoMi$er damper is maintained at its cur-
rent value.
3. If Y1 is energized, and compressor no. 1 is already ener-
gized (see Step 2) and the room thermostat calls for Y2,
compressor no. 1 continues to operate. If Y2 remains
energized for more than 20 minutes, compressor no. 2 is
energized.
NOTE: Compressor no. 2 cannot be energized unless there is a
signal for Y2 from the space thermostat.
4. If compressor no. 2 is energized, and the Y2 signal from
the thermostat is satisfied, compressors 1 and 2 are deen-
ergized. Re-asserting Y2 will start compressor no. 1 and
(after a 20-minute interstage delay) compressor no. 2.
5. If compressor no. 1 is energized and the thermostat is sat-
isfied, compressor no. 1, the OFM, and IFM are deener-
gized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
SERVICE
Cleaning —
Inspect unit interior at the beginning of each
heating and cooling season or more frequently as operating
conditions require.
EVAPORATOR COIL — Clean coil as required. Inspect coil
at beginning of heating and cooling seasons.
1. Turn unit power off. 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. Remove filters from 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, back-
flush toward return-air section to remove foreign materi-
al. Caution should be taken as to not overflow the evapo-
rator drain condensate pan.
5. Flush condensate pan after completion.
6. Reinstall economizer and filters.
7. Reconnect wiring.
8. Replace access panels.
CONDENSER COIL — Inspect coil monthly. Clean con-
denser coil annually, and as required by location and outdoor-
air conditions.
One-Row Coils — Wash coil with commercial cleaner. Clean
outer surfaces with a stiff brush in the normal manner. It is not
necessary to remove top panel.
2-Row Coils — Clean coil as follows:
1. Turn off unit power.
2. Remove top panel screws on condenser end of unit.
3. Remove condenser coil corner post. See Fig. 45. To hold
top panel open, place coil corner post between top panel
and center post. See Fig. 46.
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. 47.
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 a field-
supplied fastener.
8. Reposition the outer coil section and remove the coil cor-
ner post from between the top panel and center post.
9. 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.
BELTS — Adjust belt tension and pulley alignment at least
twice a year or more frequently as operating conditions require.
Refer to Step 9 — Adjust Evaporator for Fan Speed
for procedures.
When servicing unit, shut off all electrical power to unit to
avoid shock hazard or injury from rotating parts.
