Manual 2100-769A
Page
31 of 50
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-Y1 circuit,
pulling in compressor contactor starting compressor
and outdoor motor. R-G also make starting indoor
blower motor.
Heating Stage 2
Circuit R-Y1 & B continue to be energized. Circuit
R-Y2 makes at the thermostat energizing the 2nd stage
solenoid in the compressor.
Heating Stage 2 and Electric Heat (Up to 10KW)
Circuit R-Y1, Y2 & B continue to be energized for
heating stage 2. On the a call for electric heat, circuit
R-W2 makes at the thermostat, pulling in the heat
contactor for the strip heat.
Emergency Heat
The thermostat drops out the heat pump call. Circuit
R-W2 continues to be energized and R-W3 makes at
the thermostat, pulling in the second heat contactor, if
equipped.
Low Ambient Conditions
If the application is likely to require air conditioning
operation below 60°F outdoor conditions, a low
ambient control (LAC) kit must be installed. The LAC
kit also comes with an evaporator freeze protection
thermostat that cuts out the compressor if the
evaporator begins to freeze up.
If the unit is being installed with any ventilation
package, a Bard LAC kit must be installed.
Failure
to utilize an LAC with any heat pump can cause coil
freeze up.
Defrost Cycle
The defrost cycle is controlled by temperature and time
on the solid state heat pump control (see Figure 22 on
page 32).
When the outdoor temperature is in the lower
40°F temperature range or colder, the outdoor coil
temperature is 32°F or below. This coil temperature is
sensed by the coil temperature sensor mounted near
the bottom of the outdoor coil. Once coil temperature
reaches 30°F or below, the coil temperature sensor
sends a signal to the control logic of the heat pump
control and the defrost timer will start accumulating
run time.
After 30, 60 or 90 minutes of heat pump operation at
30°F or below, the heat pump control will place the
system in the defrost mode. Factory default setting is
60 minutes.
During the defrost mode, the refrigerant cycle switches
back to the cooling cycle, the outdoor motor stops,
electric heaters are energized and hot gas passing
through the outdoor coil melts any accumulated frost.
When the temperature rises to approximately 57°F, the
coil temperature sensor will send a signal to the heat
pump control which will return the system to heating
operations automatically.
If some abnormal or temporary condition such as a high
wind causes the heat pump to have a prolonged defrost
cycle, the heat pump control will restore the system to
heating operation automatically after 8 minutes.
The heat pump defrost control board has an option
of 30-, 60- or 90-minute setting. By default, this
unit is shipped from the factory with the defrost time
on the 60-minute pin. If circumstances require a
change to another time, remove the jumper pin from
the 60-minute terminal and reconnect to the desired
terminal. Refer to Figure 22.
There is a cycle speed up jumper on the control. This
can be used for testing purposes to reduce the time
between defrost cycle operation without waiting for
time to elapse.
Use a small screwdriver or other metallic object, or
another 1/4" QC, to short between the
SPEEDUP
terminals to accelerate the HPC timer and initiate
defrost.
Be careful not to touch any other terminals with the
instrument used to short the
SPEEDUP
terminals.
It may take up to 15 seconds with the
SPEEDUP
terminals shorted for the speedup to be completed and
the defrost cycle to start.
As soon as the defrost cycle kicks in, remove the
shorting instrument from the SPEEDUP terminals.
Otherwise the timing will remain accelerated and
run through the 1-minute minimum defrost length
sequence in a matter of seconds and will automatically
terminate the defrost sequence.
There is an initiate defrost jumper (
SEN JMP
) on the
control that can be used at any outdoor ambient during
the heating cycle to simulate a 0°F coil temperature.
This can be used to check defrost operation of the unit
without waiting for the outdoor ambient to fall into the
defrost region.
By placing a jumper across the
SEN JMP
terminals (a
1/4" QC terminal works best) the defrost sensor mounted
on the outdoor coil is shunted out and will activate
the timing circuit. This permits the defrost cycle to be
checked out in warmer weather conditions without the
outdoor temperature having to fall into the defrost region.
In order to terminate the defrost test, the SEN JMP
jumper must be removed.
If left in place too long, the
