Carrier 50HJ008-014, Инструкция по установке, запуску и обслуживанию, Страница: 28 / 40

UNITS WITH MOISTUREMISER DEHUMIDIFICATION
PACKAGE — When thermostat calls for cooling, terminals
G and Y1 and/or Y2 and the compressor contactor(s) C1
(and C2) are energized. The indoor (evaporator) fan motor
(IFM), compressor(s), and outdoor (condenser) fan motors
(OFM) start. The OFMs runs continuously while the unit is
in cooling. As shipped from the factory, MoistureMiser de-
humidification circuit is always energized. If MoistureMiser
circuit modulation is desired, a field-installed, wall-mounted
humidistat is required.
If the MoistureMiser humidistat is installed and calls for
the MoistureMiser subcooler coil to operate, the humidistat
internal switch closes. This energizes and closes the liquid
line solenoid(s) valve coils (LLSV) of the MoistureMiser cir-
cuit, forcing the hot liquid refrigerant of the liquid line to
enter the subcooler coil (see Fig. 33). As the hot liquid passes
through the subcooler coil, it is exposed to the cold supply
airflow coming off from the evaporator coil and the liquid is
further cooled to a temperature approaching the evaporator
coil leaving-air temperature. The state of the refrigerant leav-
ing the subcooler coil is a highly subcooled liquid refriger-
ant. The liquid then enters a thermostatic expansion valve
(TXV) where the liquid is dropped to a lower pressure. The
TXV does not have a pressure drop great enough to change
the liquid to a 2-phase fluid. The TXV can throttle the pres-
sure drop of the liquid refrigerant and maintain proper con-
ditions at the compressor suction valve over a wide range of
operating conditions. The liquid then enters a second fixed
restrictor expansion device for a second pressure drop to a
2-phase fluid. The liquid proceeds to the evaporator coil at
a temperature lower than normal cooling operation. This lower
temperature is what increases the latent capacity of the roof-
top. The 2-phase refrigerant passes through the evaporator
and is changed into a vapor. The air passing over the evapo-
rator coil will become colder than during normal operation
as a result of the colder refrigerant temperatures. However,
as it passes over the subcooler coil, the air will be warmed
slightly.
As the refrigerant leaves the evaporator, the refrigerant passes
a low-pressure switch in the suction line. This low-pressure
switch will deactivate the MoistureMiser package when
the suction pressure reaches 60 psig. The low-pressure
switch is an added safety device to protect against evapo-
rator coil freeze-up. The low-pressure switch will only de-
activate and open the liquid line solenoid valve in the
MoistureMiser circuit. The compressors will continue to run
as long as there is a call for cooling, regardless of the po-
sition of the low-pressure switch. The solenoid valve and
the MoistureMiser package will be reactivated only when
the call for cooling has been satisfied, the low-pressure switch
has closed, and a new call for cooling exists. The crankcase
heaters on the scroll compressors provide additional protec-
tion for the compressors due to the additional refrigerant charge
in the subcooler.
When the humidistat is satisfied, the humidistat internal
switch opens, cutting power to and opening the LLSV. The
refrigerant is routed back through the evaporator and the sub-
cooler coil is removed from the refrigerant loop.
When the thermostat is satisfied, C1 (and C2) is de-
energized and the compressor(s) and OFMs shut off. After a
30-second delay, the IFM shuts off. If the thermostat fan se-
lector switch is in the ON position, the IFM will run
continuously.
SERVICE
When servicing unit, shut off all electrical power to unit
to avoid shock hazard or injury from rotating parts.
Cleaning —
Inspect unit interior at the beginning of
each heating and cooling season or as operating conditions
require.
EVAPORATOR COIL
1. Turn unit power off. Remove evaporator coil access panel.
2. If economizer or accessory two-position damper is in-
stalled, remove economizer or two-position damper by
disconnecting economizer plug and removing mounting
screws (see Fig. 16, 17, or 24). Refer to Accessory Econo-
mizer or Two-Position Damper Installation Instructions
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, back-
flush toward return-air section to remove foreign
material.
5. Flush condensate pan after completion.
6. Reinstall economizer or two-position damper and filters.
7. Reconnect wiring.
8. Replace access panels.
CONDENSER COILS — Inspect coils monthly. Clean con-
denser coils annually, and as required by location and outdoor-
air conditions.
Clean 2-row coils 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. 34. To hold
top panel open, place coil corner post between top panel
and center post. See Fig. 35.
4. Remove device 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. 36.
5. Use a water hose or other suitable equipment to flush down
between the 2 coil sections to remove dirt and debris. Clean
the outer surfaces with a stiff brush in the normal manner.
6. Secure the sections together. Reposition the coil sections,
and remove the coil corner post from between the top
panel and center post. Install the coil corner post and coil
center 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
cooling season, or more often if operating conditions require
it. Replacement filters must be same dimensions as original
filters.
OUTDOOR-AIR INLET SCREEN — Clean screen with steam
or hot water and a mild detergent. Do not use throwaway
filters in place of screens.
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