Maytag PSA4BG024K - System Operation

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rst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rststagecallincooling,ifthesetpoint
wassatised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satised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eld,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.