6
SYSTEM OPERATION
Thermostat
The primary control for the overall cooling system is provided
by the indoor thermostat. Any standard two-stage thermostat
will be sufficient for operation. Refer to the manual for the
thermostat selected or installed for configuration and usage
details.
Blower Flow Rates
Depending on the indoor equipment installed, blower air flow
may be adjustable. When paired with a matching model air
handler or gas furnace, the airflow is set by DIP switches on
the blower control board, providing one flow for second stage
compressor speeds and a lower flow for first stage compressor
speeds. Refer to the indoor equipment manuals for instructions
on how to select the desired air flows. High stage airflows used
for equipment ratings are as follows:
• 2 ton - 810 cfm
• 3 ton - 1050 cfm
• 4 ton - 1480 cfm
• 5 ton - 1675 cfm
Refer to indoor equipment installation instructions for options,
operation, and field wiring relating to dehumidification and
humidification.
Start-Up Sequence
The recommended sequence is to provide 208/230 volt line
power to the outdoor unit first (via the disconnect), then apply 24
vac control power second. This sequence will avoid generating
potentially confusing fault codes, which will continue to be
displayed as part of fault history when the unit is subsequently
operating normally.
Run Sequence
After power-up and between cycles (after the preceding
shutdown) there will always be a five minute compressor
(re)start delay imposed. With a call for cooling and before
the compressor is turned on, the outdoor fan will run for one
minute to assure that the outdoor temperature measurement
is close to that of the ambient air. The compressor will then
ramp up to a speed selected by the capacity control scheme.
The 20 SEER air conditioner is a true variable speed unit.
Normally the compressor will operate at one of 5 cooling
speeds, each predetermined for a balance of optimum
efficiency and capacity.The outdoor fan motor will also operate
at multiple speeds, following the compressor.
The speeds used will depend on several factors, including:
• Whether first or second stage operation is called for by the
thermostat (which must be two stage-capable),
• Outdoor ambient temperature.
• The length of time the equipment has been operating during
the current cycle
• The operating speed history, for both the current and the
previous operating cycles.
For example, with a first stage call in cooling, if the setpoint
was satisfied quickly (within 20 minutes), the unit will restart
the next time at a lower speed. At a low or intermediate speed,
if the setpoint is not satisfied within 45 minutes, the speed
will be increased. If the unit cycles off after having a speed
increase, the entire next cycle will be at the higher speed.
Also, the outdoor fan will run for an extra minute after the
compressor shuts off at the end of a cycle.
Charging Operation
For charging in the field, the unit should be run with a call for
second stage cooling, with both
Y1
and
Y2
outputs energized.
This may be accomplished by setting the thermostat to cool
with a setpoint substantially lower than room temperature.
This will provide 45 minutes of operation at the nominal rating
speed (interface board display “
C4
”) before there is a speed
change (to a higher speed). If this speed change occurs before
the charging process is complete, turn the system off, turn
control power off and on again, and then restart the process.
Alternate Procedure for Charging the Air
Conditioner in Cooling Mode
With outdoor temperature above 60° F (Based on
Subcooling):
While charging based on weight is preferred, this method is
acceptable. Use this method when the outdoor temperature
is 60° F or higher to verify the correct charge. The indoor
temperature should be between 70° F and 80° F.
1. Connect the gauge manifold to the liquid and vapor service
valves. See
Figure 5 (page
12)
.
2. Start the system in cooling mode. Allow the system to run
15 minutes to stabilize.
3. Record the refrigerant pressure in psig at the liquid service
valve.
4. Record the liquid refrigerant line temperature (in ° F) at or
near the liquid service valve.
5. Using the temperature value recorded, determine the
corresponding liquid refrigerant pressure from the curve
in the charging chart appropriate for the unit model. See
Figure 6 (page
13)
.
• If the pressure measured in step 3 is less than the required
liquid refrigerant pressure determined in step 5, then
refrigerant needs to be added.
• If the pressure measured in step 3 is greater than the
required liquid refrigerant pressure determined in step 5,
then the system is over-charged.
6. Add or remove charge from the system depending on the
measurements recorded. Allow the system to stabilize for
15 minutes before taking the next readings.
