Carrier WeatherMaker 50KCQ A04 Series, Service And Maintenance Instructions

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LOSS OF CHARGE SWITCH
The system is protected against a loss of charge and low evapo-
rator coil loading condition by a loss of charge switch located
on the liquid line and a freeze protection thermostat on the in-
door coil. The switch is stem-mounted. Loss of Charge Switch
trip setting is 27 psig ± 3 psig (186 ± 21 kPa). Reset is automat-
ic at 44 ± 3 psig (303 ± 21 kPa).
Freeze Protection Thermostat trip setting is 30°F ± 5°F (–1°C
± 3°C). Reset is automatic at 45°F ± 5°F (7°C ±3°C).
SUPPLY (INDOOR) FAN MOTOR PROTECTION
Disconnect all electrical power and apply appropriate lockout/
tag-out procedures when servicing the fan motor.
Motors are equipped with an over-temperature device (Ther-
mik 1 ), internal line break, external circuit breaker or electronic
controlled circuits for overload protection. All protection
schemes are automatically reset except for units with the 2-
speed indoor fan option (VFD) or external circuit breakers.
These two protection schemes are classified as manual reset.
The type of device depends on several factors including motor
size, voltage and other options in the unit (i.e. VFD).
The Thermik device is a snap-action over-temperature protec-
tion device that is embedded in the motor windings. It is also a
pilot-circuit device that is wired into the unit’s 24-v control cir-
cuit. When this device reaches its trip set point, it opens the
24-v control circuit and causes all unit operation to stop. This
device resets automatically when the motor windings cool. Do
not bypass this device to correct trouble. Determine the cause
of the problem and correct it, then wait for the automatic reset.
The external motor overload device is a specially-calibrated
circuit breaker that is UL-recognized as a motor overload con-
troller. It is an over-current device. When the motor current ex-
ceeds the circuit breaker set point, the device opens all motor
power leads and the motor shuts down. Reset requires a manu-
al reset at the overload switch. This device (designated IFCB)
is located on the side of the supply fan housing, behind the fan
access panel.
TROUBLESHOOTING SUPPLY FAN MOTOR OVER-
LOAD TRIP
The supply fan used in the 50KCQ units is a forward-curved
centrifugal wheel. At a constant wheel speed, this wheel has a
characteristic that causes the fan shaft load to DECREASE
when the static pressure in the unit-duct system increases and
to INCREASE when the static pressure in the unit-duct system
decreases (and fan airflow rate increases). Motor overload con-
ditions typically develop when the unit is operated with an ac-
cess panel removed, with unfinished duct work, in an econo-
mizer-open mode, or a leak develops in the duct system that al-
lows a bypass back to unit return opening.
OUTDOOR FAN MOTOR PROTECTION
The outdoor fan motor is internally protected against over-
temperature.
CONTROL CIRCUIT, 24-V
The control circuit is protected against over-current conditions
by a circuit breaker mounted on control transformer TRAN.
The Control Circuit is reset manually.
COMMERCIAL DEFROST CONTROL
The Commercial Defrost Control Board (DFB) coordinates
thermostat demands for supply fan control, 1 or 2 stage cool-
ing, 2 stage heating, emergency heating and defrost control
with unit operating sequences. The DFB also provides an in-
door fan off delay feature (user selectable). See Fig. 27 for
board arrangement.
Fig. 27 — Defrost Control Board Arrangement
The DFB is located in the 50KCQ’s main control box (see
Fig. 28). All connections are factory-made through harnesses
to the unit’s CTB, to IFC (belt-drive motor) or to ECM (direct-
drive motor), reversing valve solenoids and to defrost thermo-
stats. Refer to Table 8 for details of DFB Inputs and Outputs.
Detailed unit operating sequences are provided in the Start-Up
section starting on page 55.
Fig. 28 — Defrost Control Board Location
1. Thermik is a trademark of Thermik Geratebau GmbH.
DIP
SWITCHES
SPEED-UP
JUMPERS