Carrier 50QQ - Manual (Page 8)

START-UP
The 50QQ unit compressors Eire equipped with crankcase
heaters. It is recommended that heater be energized a mini­
mum of 24 hours before starting unit. To energize heater
only, set thermostat at OFF position; turn on unit main
power at disconnect switch.
Heat Anticipator Settings for Room Thermostat—
Set
anticipator settings for room thermostat according to sepa­
rate accessory electric heater Instedlation Instructions.
Accessory Outdoor Thermostat
provides adjustable out­
door control of accessory electric heaters of 15 kW and
leirger. This thermostat makes contact when a drop in out­
door temperature occurs. It energizes a stage of electric
heat when the outdoor temperature setting is reached, pro­
vided the room thermostat is on the second stage of heat­
ing. An outdoor thermostat is recommended for the second
stage of electric heat. Refer to heat load of building and unit
capacity to determine the correct outdoor thermostat
setting.
The accessory supplemental heat relay is required when 2
outdoor thermostats are used. It is automaticeilly energized
by the manually operated supplementeil heat switch in the
indoor thermostat subbase. The indoor thermostat locks out
compressor and the relay bypasses the outdoor thermostats
for electric heater operation during heat pump shutdown.
When one outdoor thermostat is used, a supplemental heat
relay is not required. The supplemental heat switch in the
indoor thermostat subbase bypasses outdoor thermostat,
locks out compressor and activates electric heater.
MOUNT OUTDOOR THERMOSTAT-Locate maximum
of 2 outdoor thermostats in the controls section on the cen­
ter post to the left of the electric heater. Fasten with screws
in holes provided. Route capillary tube per instructions in
thermostat package.
MOUNT SUPPLEMENTAL HEAT RELAY in low-voltage
section of control box to right of low-voltage connections,
using holes provided.
To Start Unit—
Check that main power is on and that com­
pressor crankcase heater has been energized for at least 24
hours.
1. Check that heater main power is on as applicable.
2. Set selector switch at OFF.
3. Set fan switch as desired (FAN) (AUTO.).
4. Set thermostat died at the desired temperature.
5. Set selector switch at HEAT or COOL. Check system
refrigerant charge as described under Service.
Unit Single-Phase Compressors are Equipped with a Com­
pressor Start Thermistor (PTC device)—
When supply volt­
age is within 10% limit and compressor does not start,
check the start thermistor with an ohmmeter.
CHECKING START THERMISTOR
1. Shut off all power to unit and wait 10 minutes for
thermistor to cool to ambient temperature.
2. Remove thermistor from circuit.
3. Measure resistance of thermistor with ohmmeter. Nor­
mal resistance readings are 25 ohms ± 20% at 75 F
ambient temperature.
4. If ohmmeter resistance reading is not within ± 20%,
the thermistor is defective and must be replaced.
If start thermistor is good and compressor does not start,
disconnect the thermistor from starting circuit and give
compressor a temporary capacitance boost. Run compressor
for 10 minutes, then shut off and eillow system pressure to
equalize. Reconnect start thermistor and try restarting
compressor without boost capacitor. If after 2 attempts the
compressor does not start, remove thermistor and add an
accessory start capacitor and relay.
SERVICE
A WARNING
Before installing or servicing unit, turn off main power
to system. There may be more than one disconnect
switch. Turn off accessory heater power if applicable.
Electrical shock can cause personal injury or death.
Unit Controls and Safety Devices
The following controls are used on all units:
HIGH-PRESSURE RELIEF VALVE (Safety Control) is
located in compressor. Relief valve opens at a pressure dif­
ferential of approximately 450 psi between suction (low
side) and discharge (high side) to allow pressure
equalization.
INTERNAL CURRENT AND TEMPERATURE SENSI­
TIVE OVERLOAD (Safety Control) resets automatically
when internal compressor motor temperature drops to a
safe level. When an internal overload is suspected of being
open, check by using an ohmmeter or continuity tester.
DEFROST CONTROL, consisting of a control board and
defrost thermostat, interrupts normeJ system heating oper­
ation to remove frost and ice formation on outdoor coil.
Frost impairs unit performance. Defrost control simulta­
neously stops outdoor fan, energizes reversing valve sole­
noid to switch system into cooling cycle (outdoor unit as
condenser, indoor unit as evaporator), and activates acces­
sory electric heater. Unit can defrost every 90 minutes, but
will do so only if outdoor temperatures are in the frosting
temperature zone.
For heat pump to defrost, 2 conditions are necessary:
1. Defrost timer contacts must be closed.
2. Refrigerant temperature must be cold enough to cause
defrost thermostat contacts to close. Contacts close at
27 ± 5 F.
Every 90 minutes of elapsed running time, the defrost timer
contacts close for 10 seconds. If the defrost thermostat con­
tacts are closed, the unit defrosts. The defrost timer limits
defrosting period to 10 minutes. Normally the frost is
removed and the defrost thermostat contacts will open to
terminate defrosting before 10 minutes have elapsed.
Defrost thermostat contacts open at 80 ± 6 F. When
defrosting is terminated, the outdoor fan motor is energized
and reversing valve solenoid is de-energized, returning unit
to heating cycle.
The 90-minute period to check for defrost can be changed to
50 or 30 minutes by moving a jumper wire on the defrost
printed-circuit board.
HEAT PUMP CIRCUITS shown in Fig. 10 are refrigerant
flow diagrams for heating and cooling cycles.
Refrigerant Charging
A WARNING
Avoid contact with hot gas discharge line to prevent a
burn when working on compressor.