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页码 28
Manual 2100-455M 
Page  18 of 28
Phase mOnItOr
All units with three phase compressors are equipped with 
a 3 phase line monitor to prevent compressor damage 
due to phase reversal.
The phase monitor in this unit is equipped with two 
LEDs.  If the Y signal is present at the phase monitor 
and phases are correct, the green LED will light.  If 
phases are reversed, the red fault LED will be lit and 
compressor operation is inhibited.  
If a fault condition occurs, shut off main power and 
reverse two of the supply leads to the unit.  Do not reverse 
any of the unit factory wires as damage may occur.
serVIce hInts
  1. Caution owner/operator to maintain clean air filters 
at all times.  Also, not to needlessly close off supply 
and return air registers.  This reduces airflow through 
the system, which shortens equipment service life as 
well as increasing operating costs.
  2. Switching to heating cycle at 75°F or higher outside 
temperature may cause a nuisance trip of the remote 
reset high pressure switch.  Turn thermostat off then 
on to reset the high pressure switch.
  3. The heat pump wall thermostats perform multiple 
functions.  Be sure that all function switches are 
correctly set for the desired operating mode before 
trying to diagnose any reported service problems.
  4. Check all power fuses or circuit breakers to be sure 
they are the correct rating.
  5. Periodic cleaning of the outdoor coil to permit full 
and unrestricted airflow circulation is essential.
seQuence OF OPeratIOn
COOLING STAGE 1  –  Circuit R-Y makes at 
thermostat pulling in compressor contactor, starting the 
compressor and outdoor motor.  The G (indoor motor) 
circuit is automatically completed on any call for cooling 
operation or can be energized by manual fan switch on 
subbase for constant air circulation.
COOLING STAGE 2  –  Circuit R-Y1 makes at 
the thermostat energizing the 2nd stage solenoid in 
the compressor.  Default position is not energized.  
Compressor will run at low capacity until this solenoid is 
energized.
HEATING STAGE 1  – A 24V solenoid coil on reversing 
valve controls heating cycle operation.  Two thermostat 
options, one allowing “Auto” changeover from cycle to 
cycle and the other constantly energizing solenoid coil 
during heating season and thus eliminating pressure 
equalization noise except during defrost, are to be used.  
On “Auto” option a circuit is completed from R-B and  
R-Y on each heating “on” cycle, energizing reversing 
valve solenoid and pulling in compressor contactor 
starting compressor and outdoor motor.  R-G also make 
starting indoor blower motor.  Heat pump heating cycle 
now in operation.  The second option has no “Auto” 
changeover position, but instead energizes the reversing 
valve solenoid constantly whenever the system switch 
on subbase is placed in “Heat” position, the “B” terminal 
being constantly energized from R.  A thermostat 
demand for Stage 1 heat completes R-Y circuit, pulling 
in compressor contactor starting compressor and outdoor 
motor.  R-G also make starting indoor blower motor.
HEATING STAGE 2  – Circuit R-Y2 makes at the 
thermostat energizing the 2nd stage solenoid in the 
compressor.
cOmPressOr current & Pressure 
cOntrOl mODule
The compressor control module monitors compressor 
current and pressure and prevents internal overload 
trips due to low voltage or extremely high ambient 
temperatures by de-energizing the full capacity 
compressor solenoid.  The control monitors current 
to the compressor and discharge pressure.  If current 
is sensed that is in excess of 93% of the compressor 
maximum continuous current rating or pressure is 
sensed greater than 540 PSI (located on liquid line and 
is marked with Bard Part #8406-111), the compressor 
control module de-energizes the second stage solenoid 
in the compressor for a time as determined by the time 
potentiometer on the compressor control module.  This 
will drop the current draw and pressure and allow the 
compressor to run at 75 percent of capacity rather than 
not at all.  Once the time period has elapsed the full 
capacity compressor solenoid will re-energize and try 
again to run at full capacity.  If the pressure or current 
is exceeded again, the coil will again de-energize.  This 
sequence will repeat until the ambient temperature drops 
or the line voltage increases enough that the trip values 
are not exceeded.
The relay on the compressor control module is a single 
pole double throw relay.  The full capacity compressor 
solenoid connects to the common terminal of the relay.  
Once current is sensed by the compressor control 
module, the relay closes and the second stage cooling 
call (if present) is sent to the full capacity compressor 
solenoid.  This sequence prevents damage to the full 
capacity compressor solenoid by ensuring that the 
solenoid is not energized when the compressor is 
not running.  A brief time delay in this sequence also 
prevents locked rotor amperage during start-up from 
tripping the device and engaging the time delay period.