Page 13 of 21
507919-01
Issue 1946
Before final adjustment is made to the refrigerant charge,
it is imperative that proper indoor airflow be established.
Airflow will be higher across a dry coil versus a wet coil.
Blower charts are calculated with a dry or wet coil basis.
Recommended airflow is 350-450 CFM per ton (12,000
Btuh) through a wet coil. Refer to indoor unit instructions for
methods of determining air flow and blower performance.
The optimum method for checking the charge is by
weight. However the following methods may be used
to confirm the proper charge:
Cooling Mode
1. Operate unit a minimum of 10 minutes before checking
charge.
2. Measure liquid service valve pressure by attaching an
accurate gage to service port. Determine saturation
temp. from T/P chart.
3. Measure liquid line temperature by attaching an
accurate thermistor type or electronic thermometer to
liquid line near outdoor coil.
4. Calculate subcooling (saturation temp. measured
temp.) and compare with table on back of central box
cover.
Operation
Pressure Switch Connections
The unit’s automatic reset pressure switches (LO PS - S87
and HI PS - S4) are factory-wired into the control board on
the LO-PS and HI-PS terminals, respectively.
Low Pressure Switch (LO-PS)
When the low pressure switch trips, the control board will
cycle off the compressor, and the strike counter in the
board will count one strike. The low pressure switch is
ignored under the following conditions:
• during the defrost cycle and 90 seconds after the
termination of defrost
• when the average ambient sensor temperature is
below 15° F (-9°C)
• for 90 seconds following the start up of the compressor
• during “test” mode
High Pressure Switch (HI-PS)
When the high pressure switch trips, the control board
will cycle off the compressor, and the strike counter in the
board will count one strike.
Pressure Switch Settings
• High Pressure (auto reset)
- trip at 590 psig; reset
at 418.
• Low Pressure (auto reset)
- trip at 25 psig; reset at
40.
5. Add refrigerant if subcooling is lower than table.
Recover refrigerant if subcooling is high.
6. If ambient temp is lower than 60°F, check charge in
heating mode or weigh refrigerant according to name
plate data.
Heating Mode
Check charge in heating mode if ambient temp is below
60° F. Indoor temp must be between 65° and 75° F.
Follow steps (1) to (6) above and compare with heating
mode subcooling range on the table on back of central box
cover.
Charge must be rechecked again during the cooling
season.
Cold Weather Application
A cold weather accessory kit may be required for heat
pumps operating at ambient conditions below 25°F.
Supplemental heat should be provided for these conditions.
5-Strike Lockout Feature
The internal control logic of the board counts the pressure
switch trips only while the Y1 (Input) line is active. If a
pressure switch opens and closes four times during a Y1
(Input), the control logic will reset the pressure switch trip
counter to zero at the end of the Y1 (Input). If the pressure
switch opens for a fifth time during the current Y1 (Input),
the control will enter a lockout condition.
The 5-strike pressure switch lockout condition can be reset
by cycling OFF the 24-volt power to the control board or by
shorting the TEST pins between 1 and 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while the Y1 Out line is engaged,
a 5-minute short cycle will occur after the switch closes.
Demand Defrost System
The demand defrost system measures differential
temperatures to detect when the system is performing
poorly because of ice build-up on the outdoor coil. The
system “self-calibrates” when the defrost system starts
and after each system defrost cycle. The demand defrost
components on the control board are listed below.
NOTE:
The demand defrost system accurately measures
the performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates on
the outdoor coil before the board initiates defrost cycles.
