Maintenance; Fan Operation; Defrost; Cooling - Carrier 50ZH Series Installation, Start-Up And Service Instructions Manual

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Step 6--Sequence of Operation
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Fig. 17--Accessory Electric Heater Wiring
FAN OPERATION
The FAN switch on the thermostat controls indoor fan operation.
When the FAN switch is placed in the ON position, the IFR
(indoor-fan relay) is energized through the G terminal on the
thermostat. The normally-open contacts close, which then provide
power to the indoor (evaporator) fan motor (IFM). The 1FM will
run continuously when the FAN switch is set to ON.
When the FAN switch is set to AUTO, the thermostat deenergizes
the IFR (provided them is not a call li)r cooling). The contacts ()pen
and the ]FM is deenergized. The 1FM will be energized only when
them is a call lot cooling, in heat pump heating mode or if the unit
is equipped with accessory electric heat, the indoor-fan motor will
also run while the accessory electric heat is energized.
NOTE: Some units are equipped with a time-delay relay. On
these units, the indoor lhn renmins on li)r 30 seconds alter G or Y
is deenergized.
COOLING
With the thermostat subbase in the cooling position, the thermostat
makes circuit R-O. This energizes the reversing valve solenoid
(RVS) and places the unit in standby condition R(r cooling.
NOTE: The defrost control board has a 5 minute compressor
anti-short cycle time delay built in between compressor starts.
On a call lor cooling, tile compressor contactor (C) and the IFR are
energized through the Y and G terminals of the thermostat.
Energizing the compressor contactor supplies power to the com-
pressor and the outdoor (condenser) fan motor (OFM). Energizing
the 1FR provides power to the IFM.
When the need fi)r cooling has been satisfied, the OFM, compres-
sor, and IFM (FAN on AUTO) are deenergized. If the unit is
equipped with a 30-second delay (036 size only), the indoor fan
will renmin energized li)r 30 seconds alter the compressor is
deenergized. The reversing valve solenoid renmins energized.
HEAT PUMP HEATING
On a call for heat, thernmsmt makes circuits R-Y and R-G. When
compressor time delay (5-minute _+2 minutes) is completed, a
circuit is made to C, starting COMP and OFM. Circuit R-G also
energizes 1FR and starts IFM after l-second delay.
Should room temperature
continue to fall, circuit R-W is nmde
through second-stage thermostat bulb. If optional electric heat
package is used, a relay is energized, bringing on first bank of
supplemental electric heat. When thermostat is satisfied, contacts
open, deenergizing contactor and relay; motors and heaters deen-
ergize. The 1FM may be controlled by a tin(e-delay relay that keeps
the fan on fl)r 30 seconds.
DEFROST
Deli'ost board (DB) is a time and temperature comrol, which
includes a field-selectable time period between checks fl)r deli'ost
(30, 50 and 90 ndnutes). The time period is li_ctory-set at 30
minutes and should only be adjusted by a trained service person.
Electronic timer and delh)st cycle start only when contactor is
energized and defi'ost thermostat (DFT) is closed.
Deli'ost mode is identical to Cooling (((ode. The outdoor fan motor
stops because of "OFI" and "OF2" contacts opening on the defrost
board, a bank of optional electric heat turns on to warm air
supplying the conditioned space.
ELECTRIC RESISTANCE HEATING
If accessory electric heaters are installed, on a call fl)r "Emergency
Heat" the thermostat energizes W which energises the heater mlay
and in turn energizes the electric healers. The IFR is energized
which starts the indoor-fan motor. If the heaters are staged, W2 is
energized when the second stage of heating is required. When the
need fl)r heating is satislied, the heater and IFM are deenergized.
MAINTENANCE
To ensure continuing high perR(rnmnce, and to reduce the possi-
bility of premature equipment failure, periodic nmintenance nmst
be perli.)rmed on this equipment. This cooling unit should be
inspected at least once each year by a qualil]ed service person. To
troubleshoot cooling of units, reler to Troubleshooting chart in
back of book.
NOTE TO EQUIPMENT OWNER: Consult your local dealer
about the availability of a maintenance contract.
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