Supply (Indoor) Fan Motor Protection; Outdoor Fan Motor Protection; Commercial Defrost Control; Reversing Valve Control - Carrier WeatherMaster 50HCQ04-12 Service And Maintenance Instructions

HIGH PRESSURE SWITCH
The system is provided with a high pressure switch mounted on
the discharge line. The switch is stem-mounted and brazed into the
discharge tube. Trip setting is 630 psig ± 10 psig (4344 ± 69 kPa)
when hot. Reset is automatic at 505 psig (3482 kPa).
LOSS OF CHARGE SWITCH
The system is protected against a loss of charge and low evapora-
tor coil loading condition by a loss of charge switch located on the
liquid line and a freeze protection thermostat on the indoor coil.
The switch is stem-mounted. Loss of Charge Switch trip setting is
27 psig ± 3 psig (186 ± 21 kPa). Reset is automatic 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/
Tagout procedures when servicing the fan motor.
Motors are equipped with an over-temperature device (Thermik
internal line break, external circuit breaker or electronic controlled
circuits for overload protection. All protection schemes are auto-
matically reset except for units having the 2-speed indoor fan op-
tion (VFD) or external circuit breakers. These two protection
schemes are classified as manual reset. The type of device de-
pends 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 protection
device that is embedded in the motor windings. It is also a pilot-
circuit device that is wired into the unit's 24V control circuit.
When this device reaches its trip set point, it opens the 24V control
circuit and causes all unit operation to stop. This device resets au-
tomatically when the motor windings cool. Do not bypass this de-
vice to correct trouble. Determine the cause of the problem and
correct it.
The External motor overload device is a specially calibrated cir-
cuit breaker that is UL recognized as a motor overload controller.
It is an over-current device. When the motor current exceeds the
circuit breaker set point, the device opens all motor power leads
and the motor shuts down. Reset requires a manual 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 TRIPS
The supply fan used in the 50HCQ units is a forward-curved cen-
trifugal wheel. At a constant wheel speed, this wheel has a charac-
teristic that causes the fan shaft load to DECREASE when the
static pressure in the unit-duct system increases and to IN-
CREASE when the static pressure in the unit-duct system decreas-
es (and fan airflow rate increases). Motor overload conditions typ-
ically develop when the unit is operated with an access panel re-
moved, with unfinished duct work, in an economizer-open mode,
or a leak develops in the duct system that allows a bypass back to
unit return opening.

Outdoor Fan Motor Protection

The outdoor fan motor is internally protected against over-
temperature.
CONTROL CIRCUIT, 24V
The control circuit is protected against over-current conditions
by a circuit breaker mounted on control transformer TRAN. The
Control Circuit is reset manually.
1. Thermik is a trademark of Thermik Geratebau GmbH.

COMMERCIAL DEFROST CONTROL

The Commercial Defrost Control Board (DFB) coordinates ther-
mostat demands for supply fan control, 1 or 2 stage cooling, 2
stage heating, emergency heating and defrost control with unit op-
erating sequences. The DFB also provides an indoor fan off delay
feature (user selectable). See Fig. 34 for board arrangement.
1 ),
Fig. 34 — Defrost Control Board Arrangement
The DFB is located in the 50HCQ's main control box (see
Fig. 35). All connections are factory-made through harnesses
to the unit's CTB, to IFC (belt-drive motor) or to ECM (di-
rect-drive motor), reversing valve solenoids and to defrost
thermostats. Refer to Table 8 for details of DFB Inputs and
Outputs.

Reversing Valve Control

The DFB has two outputs for unit reversing valve control. Opera-
tion of the reversing valves is based on internal logic; this applica-
tion does not use an "O" or "B" signal to determine reversing
valve position. Reversing valves are energized during the cooling
stages and the defrost cycle and de-energized during heating cy-
cles. Once energized at the start of a cooling stage, the reversing
valve will remain energized until the next heating cycle demand is
received. Once de-energized at the start of a Heating cycle, the re-
versing valves will remain de-energized until the next cooling
stage is initiated.

Compressor Control

The DFB receives inputs indicating Stage 1 Cooling, Stage 2
Cooling (sizes 08 - 12) and Stage 1 Heating from the space ther-
mostat or unit control system (PremierLink or RTU Open); it gen-
erates commands to start compressors with or without reversing
valve operation to produce Stage 1 Cooling (one compressor on
08-12 sizes), Stage 2 Cooling (both compressors run on 08-12 siz-
es) or Stage 1 Heating (both compressors run on 08-12 systems.
The 04-07 systems have only one compressor). On 2-Stage 07
units, Stage 1 Cooling operates compressor unloaded (67%) and
Stage 2 Cooling operates compressor at full load (100%).
21
DIP
Switches
Speed-Up
Jumpers