System Operation - Maytag Amana PMH Series Service And Troubleshooting

SYSTEM OPERATION

of above 33 degrees. Once above 33 degrees the unit will
return to heat pump operation on the next call for heat.
When the room temperature has reached the desired set
point, electric heat or compressor will shut off and the fan
will continue to run for approximately 30 seconds and then
shut off.
NOTE:
The heat pump and electric heat DO NOT operate together,
it is either in electric heat or heat pump mode.
Control Board Characteristics
• Automatic 3-minute Compressor Lockout - After the
compressor cycles off, it will not restart for three
minutes. This feature is enabled in standard or remote
thermostat control.
• Compressor lock-in feature- Whenever the compressor
is switched from off to on because the room tempera-
ture has risen above or fallen below the specified limit
it will remain on for at least four minutes. However , if
the thermostat point is changed during the four minutes
this lock in feature is overridden.
• Automatic 2nd Stage Electric Heat (Heat Pump Mod-
els)- If the room temperature falls to 4°F below the set
point temperature, the reverse cycle heat pump is shut
off and the strip heat is turned on.
• Automatic Freeze Protection - Whenever power is
supplied to the unit and the master switch is in the ON
position, automatic freeze protection is active. If the
thermistor senses temperature below 40°F+/-5°F, the
fan motor and electric strip heat (or hydronic heat, if
applicable) are switched on. The heater and fan will
remain on until the Thermistor senses a temperature of
43°F.
• Remote Thermostats - Always use an approved ther-
mostat supplied by the manufacturer. A wall thermostat
that has not been approved by the manufacturer may
not work correctly with this unit.
• Remote Functions - All functions are controlled by a
wall mounted thermostat.
• Remote Fan- When GL terminal is connected to R
terminal the remote fan speed is switched to low. GH
terminal connected to the R terminal fan speed is
switched to high.
• Fuse Protection- The fuse protection has been maxi-
mized on the 24 volt circuit so accidental groundings
of the external terminals will not result in a burned out
board. The unit may be operated in standard mode
if the fuse is blown. There will be an auxiliary fuse
supplied with the board. It will be attached to the main
fuse by a plastic clip. The fuse is a 500 ma fuse. When
replacing the fuse always use the correct fuse part
#M0804205.
• Random Delay - When the master switch is turned on
or power is reapplied to the control, all functionality will
be locked out for a random period between two and
four minutes, if Y or W inputs are active in remote or
the mode switch is set to HI/LO heat or cool. The delay
can be avoided if the front desk terminals are closed
for more than two seconds, or the mode switch is in the
off or fan only position.
• Indoor Ambient Thermistor- The Indoor Ambient
Thermistor senses actual room temperature.
• Indoor/Outdoor Coil Thermistors- In the cooling mode,
if the compressor is engaged continuously for 20
minutes and the Indoor Coil Thermistor is below 30
degrees the compressor is disengaged until the ICT
rises above 45 degrees. The Outdoor Coil Thermistor
senses coil temperature which correlates to outdoor air
temperature. Heat pump operation can operate as low
as 24°F outdoor temperature depending upon humidity
conditions and/or the balance point of the system. After
defrost is initiated, the compressor remains off for at
least thirty minutes and resumes operation when the
outdoor coil temperature reaches 33°F. Electric resis-
tance heat will maintain the ambient room temperature
anytime the temperature falls 4°F below the room set
point temperature.
• Load Shedding-The IN & COM terminals are used for
load shedding. A switch can be added to close the cir-
cuit to lock out the compressor and electric heat when
the power company or energy management system is
trying to reduce its load for a specified time.
• Sample Before Start - The SBS routine is used in the
cooling mode. This routine runs the unit fan on low
speed for up to 120 seconds. The sample fan is abort-
ed if compressor demand is detected. To avoid unnec-
essary sampling the period between samples will be
based on specific room conditions. The default sample
before start period after a power up is 5 minutes. The
period is corrected every time a sample run is com-
pleted without a compressor demand. The minimum
sample period is 5 minutes and the maximum period is
15 minutes.
• Front Desk Control - The front desk control termi-
nals are IN and COM. These terminals will provide a
connection for a user supplied switch that will allow the
operation of the unit to be remotely defeated.
• Transfer Fan- A transfer fan may be used if a user sup-
plied relay is connected to IN and COM. Make sure the
relay is a manufactured approved relay. The relay will
be energized whenever the blower/fan relay is ener-
gized.
• Emergency Hydronic Heat - A switch can be added to
the IN & COM terminals to close the circuit to enable
the fan, enable the heater relay and lockout the com-
pressor to continue minimum operations with auxiliary
power, if the main power goes out.
OPERATING CONTROLS
Users Controls
A 7 button touch key pad, located behind the control
door, controls both temperature and operation mode. The
key pads can be used alone or in combination.
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