170761-UIM-B-0406
Unitary Products Group
17
Auxiliary Heat Defrost Operation – Fossil Fuel Mode with
Bonnet Sensor
With a bonnet sensor present the control will energize W1 Out and W2
Out 45 seconds prior to the initiation of the defrost cycle.
During defrost operation, if the bonnet sensor input reaches 109F, the
control will de-energize W1Out and W2Out. The control will re-energize
W1Out and W2Out when the bonnet sensor input drops below 90F
again and the defrost cycle is still in process.
If a call for heating (Y1) is still present after the defrost cycle has termi-
nated, the control will continue to energize W1 Out and W2 Out after
the defrost cycle has been terminated until the bonnet sensor reaches
109F. When the bonnet sensor reaches 109F after the defrost cycle has
terminated, the control will de-energize W1 Out and W2 Out and will not
re-energize them during this call for heat. That is, once the defrost cycle
has terminated, the control will not cycle W1 Out and W2 Out with the
bonnet sensor.
The control will begin normal heat pump heating mode operation upon
termination of the defrost cycle.
Auxiliary Heat Defrost Operation – Fossil Fuel Mode with-
out Bonnet Sensor
If the control is in fossil fuel mode and senses that no bonnet sensor is
present, it will energize W1 Out and W2 Out immediately when the
defrost cycle is initiated. If a call for heating (Y1) is still present after the
defrost cycle has terminated, the control will de-energize W1 Out and
W2 Out immediately and return to normal heat pump mode operation.
In this mode the control will energize the fossil fuel furnace only during
defrost and not provide any comfort enhancements during the transi-
tion. The heat pump and furnace will not operate at the same time if the
bonnet sensor is not in place.
Pipe Freeze Protection Timer – Fossil Fuel Mode Operation
The control starts a four hour timer when a call for compressor opera-
tion and auxiliary heat (Y1 + W) is received. If the outdoor temperature
is above the balance point, the control will energize the compressor
instead of the auxiliary heat outputs. If the call for compressor operation
and auxiliary heat is still present after the timer expires, the control will
energize W1 Out and W2 Out and de-energize the compressor regard-
less of the balance point setting. The control will keep the W1 Out and
W2 Out signals energized until the Y1 signal is removed. That is, the
control will lock into auxiliary heat furnace operation until the room ther-
mostat is satisfied. The purpose of this feature is to prevent the pipes in
a home from freezing if the balance point is set too low and the heat
pump cannot heat the home using compressor operation only. This will
be a benefit if a home is not occupied and a compressor problem
occurs. The control will also store and display a fault flash code when
the pipe freeze timer has expired.
HIGH-PRESSURE SWITCH FAULT
The heat pump is equipped with a high-pressure switch that is con-
nected to the control at the HPS terminals. If the high-pressure switch
opens for more than 40 milliseconds, the control will de-energize the
compressor and store and display the appropriate fault code. If the
pressure switch closes and a thermostat call for compressor operation
is present, the control will apply the five-minute anti-short cycle delay
timer and start the compressor when the timer expires.
When the compressor is started following a high-pressure switch fault,
the control will start a six-hour timer based on accumulated compressor
run time. If the control senses another opening of the high-pressure
switch before the timer expires, it will cause a soft lockout condition.
The second opening of the high-pressure switch must be greater than
160 milliseconds for the lockout to occur. If the second opening is
between 40 and 160 milliseconds, the control will de-energize the com-
pressor but not cause a soft lockout condition. If the control does not
sense a second high-pressure switch opening before the six-hour timer
expires, the timer and counter will be reset.
LOW-PRESSURE SWITCH
The heat pump is equipped with a low-pressure switch which is con-
nected to the control at the LPS terminals. If the low-pressure switch
opens for more than five seconds, the control will cause a soft lockout
condition and display the appropriate fault codes. However, the control
will ignore the low pressure switch input and not cause a soft lockout
condition if it opens during the following conditions.
•
Defrost operation
•
First two minutes of compressor operation
•
Two minutes following the completion of a defrost cycle
•
TEST input shorted with Y1 input energized
DISCHARGE LINE TEMPERATURE SENSOR
(OPTIONAL)
The heat pump may be equipped with an optional discharge line tem-
perature sensor. If a discharge sensor is present, the control will pro-
vide the following features.
High Discharge Line Temperature
If the control senses a discharge line temperature reading of 263F for
30 seconds continually, it will cause a soft lockout condition. If the dis-
charge line temperature drops below 263F during the 30-second timer,
the control will reset the 30-second timer and restart the timer if the dis-
charge line temperature again exceeds 263F.
Low Discharge Line Temperature
The control will begin a sixty-minute timer when either of the following
conditions are met.
•
The discharge line temperature has not reached 90F after eight
minutes of accumulated compressor run time.
•
The discharge temperature has not reached 90F after fifteen min-
utes of accumulated compressor run time following the exit of a
defrost cycle.
If the discharge line temperature has not reached 90F after the sixty-
minute timer has expired, the control will cause a soft lockout condition.
The control will reset the sixty-minute timer upon expiration and when
the compressor starts. The timer is reset when the compressor starts
and is only restarted if one of the two conditions shown above are met.
The low discharge temperature fault indicates that the outdoor coil is
too cold during heating operation. The lockout is intended to prevent
refrigerant flooding back to the compressor.
IMPORTANT: The discharge sensor must be well insulated and
installed properly to prevent nuisance lockouts from occurring.
INDICATIONS OF PROPER OPERATION
Cooling
Cooling operation is the same as any conventional air conditioning unit.
1.
The outdoor fan should be running, with warm air being dis-
charged from the top of the unit.
2.
The indoor blower (furnace or air handler) will be operating, dis-
charging cool air from the ducts. Coils or other parts in the air cir-
cuit should be cleaned as often as necessary to keep the unit
clean. Use a brush, vacuum cleaner attachment, or other suitable
means.
3.
The vapor line at the outdoor unit will feel cool to the touch.
4.
The liquid line at the outdoor unit will feel warm to the touch.
Heating
Indications of proper Heating operation is as follows:
1.
The outdoor fan should be running, with cool air being discharged
from the top of the unit.
2.
The indoor blower (furnace or air handler) will be operating, dis-
charging warm air from the ducts.
3.
The vapor line at the outdoor unit will feel warm to the touch.
4.
The liquid line at the outdoor unit will feel cool to the touch.
