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When the heat pump is on the heating cycle, the outdoor coil is
functioning as an evaporator. The temperature of the refrigerant in
the outdoor coil must be below the temperature of the outdoor air in
order fo extract heat from the air. Thus, the greater the difference in
the outdoor temperature and the outdoor coil temperature, the
greater the heating capacity of the heat pump. This phenomenon
is a characteristic of a heat pump. It is a good practice to provide
supplementary heat for all heat pump installations in areas where
the temperature drops below 45 ° F. It is also a good practice to
provide sufficient supplementary heat to handle the entire heating
requirement should there be a component failure of the heat pump,
such as a compressor, or refrigerant leak, etc.
Since the temperature of the refrigerant in the outdoor coil on the
heating cycle is generally below freezing point, frost forms on the
surfaces of the outdoor ceil under certain weather
conditions of
temperature and relative humidity. Therefore, it is necessary to re-
verse the flow of the refrigerant to provide hot gas in the outdoor
ceil to melt the frost accumulation. This is accomplished by revers-
ing the heat pump to the cooling cycle. At the same time, the out-
door fan stops to hasten the temperature rise of the outdoor coil
and lessen the time required for defrosting. The indoor blower
continues to run and the supplementary heaters are energized.
DEFROSTCONTROL
During operation the power to the circuit board is controlled by a
temperature sensor, which is clamped to a feeder tube entering the
outdoor ceil. Defrost timing periods of 30,60 and 90 minutes may
be selected by connecting the circuit board jumper to 30, 60 and 90
respectively. Accumulation
of time for the timing period selected
starts when the sensor closes (approximately 31 ° F), and when the
wall thermostat calls for heat. At the end of the timing period, the
unit's defrost cycle will be initiated provided the sensor remains
closed. When the sensor opens (approximately 75 ° F), the defrost
cycle isterminated and the timing period is reset. If the defrost cycle
is not terminated due to the sensor temperature, a ten minute over-
ride interrupts the unit's defrost period.
SUGGESTED
FIELD TESTINGFrROUBLE
SHOOTING
1. Run unit in the heating mode (room thermostat calling for
heat).
2. Check unit for proper charge. Note: Bands of frost on the
condenser coil indicate low refrigerant charge.
3. Shut off power to unit.
4. Disconnect outdoor fan by removing the purple lead wire
from "DF2" on defrost control. On 460V units, remove the
red wire on DF2.
5. Restart unit and allow frost to accumulate.
6. After
a few minutes of operation,
the unit's defrost
thermostat should close. To verify this, check for 24 volts
between "DFT" and "C" on board. If the temperature at the
thermostat is less than 28 ° F and the thermostat is open,
replace the unit's defrost thermostat, as it is defective.
7. When the unit's defrost thermostat has closed, short the
test pins on the defrost
board until the reversing valve
shifts, indicating defrost.
This should take up to 21
seconds depending on what timing period the control is
set on. After defrost initiation, the short must instantly be
removed or the unit's defrost period will only last 2.3
seconds.
8. After the unit's defrost thermostat has terminated, check
the defrost thermostat for 24 volts between "DFT" and "C".
The reading should indicate 0 volts (open sensor).
9. Shut off power to unit.
10. Replace outdoor fan motor lead to terminal "DF2" on defrost
board and turn on power.
AIRFLOW MEASUREMENTANDADJUSTMENT
After reviewing Duct Work section, proceed with airflow measure-
ments and adjustments. The unit blower curves (see Specification
Sheets) are based on external static pressure (ESP per in/wc). The
duct openings on the unit are considered internal static pressure.
As long as ESP is maintained, the unit will deliver the proper air up
to the maximum static pressure listed for the CFM required by the
application (i.e. home, building, etc.)
In general, 400 CFM per ton of cooling capacity is a rule of thumb.
Some applications depending on the sensible and latent capacity
requirements may need only 350 CFM or up to 425 CFM per ton.
Check condition space load requirements (from load calculations)
and equipment expanded ratings data to match CFM and capacity.
After unit is set and duct work completed, verify the ESP with a
1-inch inclined manometer with pifot tubes or a Magnahelic gauge
and confirm CFM to blower curves in the Specification Sheets. All
units have three-speed blower motors. If low speed is not utilized,
the speed tap can be changed to medium or high speed.
NOTE: Never run CFM below 350 CFM per ton, evaporator freezing
or poor unit performance is possible.
SPEED TAP ADJUSTMENTS
FOR INDOOR BLOWER
MOTOR
PSC Motor
Adjust the CFM by changing the speed tap of the indoor blower
motor at the EBTDR "COM" connection (or EMR Terminal 1 for
460V units) with one of the speed taps on =M1" or =M2". (Black-High
Speed, Blue-Medium Speed, Red-Low Speed.)
X-13 Motor
Adjust the CFM by changing the 24V low voltage lead at the speed
terminal block on the motor. (T1-Low Speed, T2 and T3-Medium
Speed, T4 and T5-High Speed).
See Specification
Sheet for GPC/GPH model series for CFM vs
ESP tables.
REFRIGERANT
CHARGE CHECKS
After completing airflow measurements and adjustments, the unit's
refrigerant charge must be checked.
The unit is factory charged
based on 400 CFM per ton at minimum ESP per ARI test conditions
(generally between .15 - .25 ESP).
When air quantity or ESP is
differs from this, charge must be readjusted to the proper amount.
All package units are charged to the superheat method at the com-
pressor suction line (these are fixed orifice devices).
For charging in the warmer months, 10°F superheat at the com-
pressor is required at conditions:
95°F outdoor ambient (dry bulb
temperature),
80°F dry bulb / 67°F wet bulb indoor ambient, approxi-
mately 50% humidity. This superheat varies when conditions vary
from the conditions described.
A superheat charge chart is available for other operating conditions.
Use it to provide the correct superheat at the conditions the unit is
being charged at.
After superheat
is adjusted it is recommended
to check unit sub-
cooling at the condenser ceil liquid line out. in most operating con-
ditions 10 - 15°F of sub-ceoling is adequate.
10
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