Panasonic Cu 3ke19nbucu Technical Service Manual

							7.  FUNCTIONS
7-1.  Explanation of Functions
The numerical values such as temperature, frequency, time and current in parentheses are an example 
of CU-4KE31NBU and the values are different from the other models.
Control/conditions
INITIAL
Breaker is ON. Power is supplied to the indoor and outdoor unit 
control circuits, however the unit remains stopped.
Positioning of the outdoor unit electric expansion 
valve is performed.
The ON/OFF operation 
button on the remote 
controller is pressed.If automatic operation mode has been selected 
with the remote controller, operation begins in 
HEAT, SENSOR DRY, or COOL mode 
depending on the room temperature and 
outdoor temperature at the time operation starts.
Depending on the operational mode, refer to the HEAT, SENSOR DRY, or COOL item.This applies in the case of automatic 
HEAT/COOL operation.
HEAT
Unit operation Explanation
The ON/OFF operation 
button on the remote 
controller is pressed.The unit is forced to stop for 3 minutes after 
the power is turned ON, or 3 minutes after the 
compressor stops, in order to protect the 
compressor.
The frequency is increased at the rate of 1 Hz 
every 0.5 seconds. Operation lamp illuminates.
Indoor fan is stopped to prevent cold air from 
being emitted.
Outdoor unit begins operating after 
forced-stop is canceled.
This is in order to stabilize the return of oil to the 
compressor. When the frequency reaches    Hz,frequency 
increases are stopped for a period of    seconds. 
(Refor to Table 2 "Freguency control".)
If the indoor and outdoor temperatures are high, 
the current peak cut-off activates, stopping any 
increases in frequency. The frequency then increases.
The thermostat turns 
OFF.The outdoor unit stops. (It does not stop if the 
thermostat for another indoor unit is ON.)
Approximately 30 seconds after the 
thermostat turns OFF, the indoor fan is 
stopped.The indoor fan is stopped.
The indoor and outdoor 
temperatures are high.The outdoor unit starts automatically after 3 
minutes.
During these 3 minutes, a low-pressure 
pressure balance is achieved, allowing the 
compressor to start more easily.In order to protect the compressor, the outdoor 
unit will not operate for 3 minutes after the 
thermostat turns OFF, even if the room 
temperature drops below the desired 
temperature. The room temperature 
has reached the desired 
temperature.Operating frequency is stabilized in order to 
maintain a comfortable environment. The indoor temperature and the remote 
controller temperature setting are 
approximately equal.
Depending on the relationship between the 
remote controller temperature setting and the 
room temperature, the compressor may stop 
temporarily (in other words, the thermostat 
may turn OFF). When the indoor coil temperature rises,
the compressor starts,
the outdoor fan starts,
and the indoor fan changes from "LL" 
to the set fan speed.
The amount of heat pump exceeds the amount 
of heat radiation from the room.
Therefore, there is no need to further increase 
the compressor capacity, and the frequency is 
stabilized or lowered.The frequency is not increased, even if 
there is a difference between the room 
temperature and the desired temperature.
In some cases, the frequency may be 
decreased.
NOTE
71 
						

							Control/conditions
HEAT
When defrost operation 
begins, frost has formed 
on the outdoor unit 
(when the ambient air 
temperature is low).Defrost operation begins based on outdoor 
heat exchanger temperature and outdoor 
air temperature conditions.
Non-stop defrost (Refer to Fig. 1)
1. After HEAT operation begins, the temperature 
of the outdoor heat exchanger is at or below the 
L1 line for 35 minutes.
(If outdoor air temperature is less than 26.6 °F,
the time is 48 minutes) 
2. After HEAT operation begins, the temperature 
of the outdoor heat exchanger is at or below the 
L2 line for 120 minutes.
The 4-way valve remains ON during defrost. Non-stop defrost
Unit operation Explanation
The outdoor fan stops and the solenoid 
valve turns ON, allowing the refrigerant to
bypass the indoor unit. Indoor fan : Stopped
Outdoor fan : Stopped
Compressor : 80 Hz
Solenoid valve (for hot gas bypass): ON
4-way valve : Remains ON
Operation lamp : Red and orange ON 
                            alternately
Defrost release Indoor fan turns ON.
After 10 seconds, the solenoid valve 
(for hot gas bypass) turns OFF.
When the cold air feel has disappeared, 
the indoor fan starts and gradually increases 
speed until it reaches the set speed.
STOP
[Clean defrost]
Defrost is performed 
when the outdoor unit is 
stopped, and the 
temperature of the 
outdoor unit coil is at or 
below the L1 line. 
(Refer to Fig. 1.)All indicator lamps turn OFF. The indoor and 
outdoor units stop.
The operating frequency during defrost is 
80 Hz. (Frequency is lowered if the current 
peak cut-off function is activated.)
The maximum length of a single defrost 
operation is 12 minutes.
For the outdoor heat exchanger temperature 
conditions for ending defrost, refer to Table 1.
Operation is restarted 
within 4 hours (only when 
AUTO mode is selected 
with the remote 
controller).Within 4 hours after operation was stopped, it is 
assumed that there has been no significant 
change in the indoor and outdoor temperatures, 
and the previous conditions (HEAT) are stored. Starts operating in the same operating mode 
(HEAT) and with the same temperature 
settings as before operation was stopped.
Operation starts after 4 
hours or more have 
passed.New operation begins based on the 
temperature conditions at the time the 
ON/OFF button is pressed.
The thermostat turns ON. The unit operated before, and the temperature of 
the indoor heat exchanger is relatively warm.
Therefore,the fan speed may start at the set fan 
speed at the same time that the thermostat turns 
ON. The indoor unit is stopped.
72 
						

							Control/conditions
COOL
The ON/OFF operation 
button on the remote 
controller is pressed.
The room temperature 
has reached the 
desired temperature.The outdoor unit does not operate for 3 minutes 
even after the breaker is turned ON.
This is in order to stabilize the return of oil to the 
compressor. The outdoor unit starts.
(Compressor and the outdoor fan start.)
When the frequency reaches    Hz, 
frequency increases are stopped for a period 
of    seconds. (Refer to Table 2.)
If the indoor and outdoor temperatures are high, 
the current peak cut-off activates, stopping 
any increases in frequency. The frequency then increases.
Operating frequency is stabilized in order to 
maintain a comfortable environment. The indoor temperature and the desired 
temperature are approximately equal.
The thermostat turns 
ON again. After 3 minutes, the outdoor unit begins operating 
automatically.
During these 3 minutes, a pressure balance is 
achieved, allowing the compressor to start 
more easily. After the thermostat turns ON again, the 
outdoor unit will not operate for 3 minutes, 
even if the room temperature increases 
above the desired temperature.
Operation is restarted 
within 4 hours (only when 
AUTO mode is selected 
with the remote 
controller).Within 4 hours after operation was stopped, it is 
assumed that there has been no significant 
change in the indoor and outdoor temperatures, 
and the previous conditions (COOL) are stored. Starts operating in the same operating mode 
(COOL) and with the same temperature 
settings as before operation was stopped.
Operation starts after 4 
hours or more have 
passed.New operating mode is determined based on 
the temperature conditions at the time the 
ON/OFF operation button is pressed.
Stop All indicator lamps turn OFF. The indoor and 
outdoor units stop.
Freeze prevention In order to protect against freezing, the 
compressor stops temporarily, until the 
temperature of the indoor heat exchanger has 
risen.
The thermostat turns
OFF.The outdoor unit stops. (It does not stop if the
thermostart for another indoor unit is ON.)
Unit operation Explanation
The operation lamp illuminates.
The indoor fan operates at the set fan speed.
The outdoor unit stops.
When the temperature of the indoor heat 
exchanger drops to approximately 35.6 °F 
or below, the compressor turns OFF, the 
outdoor fan turns OFF, and the indoor fan 
continues operating with no changes.
Approximately 3 minutes later, if the 
temperature of the indoor heat exchanger 
is adove 46.4 °F, the system returns to its 
original conditions.
The frequency is increased at the rate of 0.5 
Hz every 1 seconds.
Table 1
Outdoor heat
exchanger temperature (°F)
Fig. 1
Outdoor air
temperature (°F) (- 4) 0
(21.2)
(19.4)
(-11.2)
(-13.0) L2
L1
Temperature of releasing
*1 The temperature for releasing of defrosting is (68 °F) or higher when the 
outdoor air temperature is less than 32 °F. Defrost operation time
Heat exchanger
temperature for 
releasing defrosting
Less than 2 minutes 2 minutes or more
No releasing 57.2 °F or higher (*1)
73 
						

							Control/conditions
SENSOR 
DRY
(1/f fluctuation fan)
The ON/OFF operation 
button on the remote 
controller is pressed.The outdoor unit does not operate for 3 minutes 
even after the breaker is turned ON.
This is in order to stabilize the return of oil to the 
compressor. The outdoor unit starts.
(Compressor and the outdoor fan start.)
When the frequency reaches    Hz, 
frequency increases are stopped for a period 
of    seconds. (Refer to Table 2.)
DRY B operation
If the indoor and outdoor temperatures are high, 
the current peak cut-off activates, stopping 
any increases in frequency. The frequency then increases.
Unit operation Explanation
The operation lamp illuminates.
The indoor fan operates at the set fan speed.
The outdoor unit stops.
The room temperature 
reaches the desired 
temperature, and there 
is no need for further 
cooling.Operating frequency is stabilized in order to 
maintain a comfortable environment.
The room temperature is 
59 °F or higher, and is 
slightly too cold.
The compressor operates on a 3-minutes ON, 
6-minutes OFF cycle, to prevent the room 
temperature from dropping too much. DRY operation starts
DRY A operation
The room temperature is 
below 59 °F.When monitoring operation begins, the 
compressor stops, and the indoor fan operates at 
"LL" (very low) speed. Monitoring operation begins.
The indoor fan changes between "Low" 
and "LL" (very low) over a 6-minute cycle. 
This is 1/f fluctuation fan operation. 
(Refer to Fig. 2.)
The indoor fan changes between "Low" 
and "LL" (very low) over a 6-minute cycle. 
This is 1/f fluctuation fan operation.    
After appoximately 3 minutes, the 
compressor turns OFF, the outdoor fan 
turns OFF, and the indoor fan turns OFF.
After approximately 6 minutes, the 
conditions return to (1). (1)
(2)
(3)
The frequency is increased at the rate of 0.5 
Hz every 1 seconds.
Operates to effectively dehumidify the air while 
not excessively reducing the indoor 
temperature.
The indoor unit operates at 1/f fluctuation fan 
operation, at a fan speed that does not cause 
a chilly feeling.
Frequency control
    (Hz)
(25) Hz
(35) Hz
(45) Hz
(55) HzOutdoor air temperature is below 32 °F.
(120) seconds
(60) seconds
(60) seconds
(180) seconds
Table 2
     (senconds)
Outdoor air temperature is 32 °F or higher.
(60) seconds
(30) seconds
(30) seconds
(90) seconds
74 
						

							1/f fluctuation fan
250
200
6-minute cycle
Fig. 2
150
100 (Step)
50
0
75 
						

							< Low Ambient Cooling Operation >
When the mode is switched from cooling opration to low ambient cooling operation,
the compressor is stopped for 150 seconds temporarily.
Outdoor fan speed [ rpm ]
Outdoor air temperature32 °F ( °C )
When the mode has been switched to low ambient cooling operation,
the outdoor fan speed is lowered as the outdoor air temperature falls.
When the outdoor air temperature reaches 57.2 °F (14 °C ) or less during the cooling operation,
the operation mode is switched to low ambient cooling operation.
The following protective actions are available to prevent the compressor from operating
with abnormal loads.
At that time, they initiate thermo-off ( stopping the outdoor unit ) of the air conditioner.
When the outdoor air temperature reaches 62.6 °F (17 °C ) or more during the low ambient
cooling operation, the operation mode is switched to cooling operation.
8.6 (-13)14 (-10)
Compressor
Indoor fanOFF
ON ON Outdoor air temp.
 °F ( °C )
ON
76 
						

							7-2.  Protective Functions
7-2-1.  Defrost Detection and Release
(2) Clean defrost
If all indoor units are stopped during HEAT operation, and frost is detected at the L1 line, and the 
conditions for defrost are met, then defrost operation occurs, and the unit stops after defrost is completed. (1) Non-stop defrosting
Heating operation
NOTEDefrost does not occur during HIGH POWER operation.
If other stopped indoor units are started during defrost operation, they begin operating in 
defrost mode.
Frost detection
Non-stop defrosting
Releasing of defrosting
Defrosting sequence 4-way valve ON
Defrost detection occurs in either of the following cases:
The temperature of the heat exchanger remains at or below 
the L1 line for 35 minutes after the start of HEAT operation.
Compressor
Outdoor fan
Solenoid valve 
(for hot gas bypass)
Temperature of the outdoor heat exchanger is at or above the 
temperature shown in the table below.
Temperature of releasing
*1 The temperature for releasing of defrosting is (68 °F) or higher when the 
outdoor air temperature is less than 32 °F. Defrost operation time
Defrost operation has continued for 12 minutes (max. length). Indoor fan(80 Hz) operation (4-way valve ON)
OFF
ON
OFF
The temperature of the heat exchanger remains at or below 
the L2 line for 120 minutes after the start of HEAT operation.
Outdoor heat
exchanger temperature (°F)
Outdoor air
temperature (°F) (- 4) 0
( 21.2)
( 19.4)
(-11.2)
(-13.0) L2
L1
Less than 2 minutes 2 minutes or more
No releasing 57.2 °F or higher (*1)
The numerical values such as temperature, frequency, time and current in parentheses are an example 
of CU-4KE31NBU and the values are different from the other models.NOTE
Heat exchanger
temperature for 
releasing defrosting
77 
						

							7-2-2.  Current Control
The operating current may rise as a result of causes including increasing heating or cooling loads or decreases in power 
voltage. In these cases, the operating frequency is automatically reduced, or operation is stopped, in order to control 
the operating current so that it is (20 A) or less.
The operating frequency is reduced automatically, or operation is stopped, in order to control the operating 
current so that it is at or below the values shown in the table below.
(20A)
HEAT Power breakers and fuses will not be tripped.
Operation can continue during this period with somewhat reduced heating or cooling capacity.
Operation at normal capacity is restored when the cause of the current rise is eliminated.
Description of function
•
•
•
Example of operation for heating
Current(A)
Frequency (Hz) Trip
Hz reduction
Hz increase
prohibitHz reduction
Hz increase prohibit
Hz reduction
Hz increase prohibit
(16)
(15.6)
0
(30)Example of operation during cooling
Frequency
Frequency CurrentStops operation
Approx.3 minutesPower Point C
Point B
Point A (20A)
(17A)
(16.6A)
Target
frequency
Operates at the target frequency at Point A and below.
Stops increases to the frequency between Points A and B.
Reduces the frequency by 1 Hz per 0.5 seconds when Point B is exceeded.
Stops operation, and restarts it appoximately 3 minutes later, if Point C is exceeded.
(May operate when sudden voltage fluctuations occur.    Indicates trouble.) •
•
•
•
As a result:
(1) Automatic frequency control
The operating frequency upper limits shown in the figure below are established for frequency reduction and 
increase-prohibit.
(2) Current control
NOTE
During defrost operation, the COOL current setting value is used.
COOL
(20.0) (20.0)
(17.0) (17.0)
(16.6) Point C (peak cut trip)
Point B (Hz reduction)
Point A (Hz increase prohibit) (16.6)
78 
						

							7-2-5.  Control at HEAT Start-up
If HEAT operation is started when the outdoor air temperature is 59 °F or below, the unit operates at the HEAT start-up 
frequency (70 Hz or above).
Reset conditions
The compressor frequency exceeds the start-up frequency of (70 Hz).
The compressor thermostat is OFF.
Frequency reduction for indoor high-load control has occurred.
The outdoor air temperature is above 59 °F.
The main-unit switch on one or more indoor units is set to TEST run. (1)
(2)
(3)
(4)
(5)
(230)
(223)
(212)Trip
5Hz every 30 sec. reduction
2Hz every 30 sec. reduction
No controlIncrease
prohibit range
(Hz reduction) (°F)
Compressor discharge temperature(194)
Within the increase-prohibit range, the range changes 
to the Hz reduction range (2 Hz every 30 seconds) if 
the compressor temperature rises by 4 °F. * Operation starts at (8 Hz), and the start current is less than the normal operating  current. This prevents the flickering 
of fluorescent lights or television screens that occurs when ordinary A/C units start.
7-2-3.  Low Start Current
To protect the compressor coil from overheating, the operating frequency is controlled based on the compressor 
discharge temperature.
7-2-4.  Compressor Temperature Control
79 
						

							8.  TROUBLESHOOTING (BEFORE CALLING FOR SERVICE)
8-1.  Precautions before Performing Inspection or Repair
Both the indoor unit and outdoor unit include electronic control circuits. 
Be sure to pay attention to the following before inspecting or repairing the 
outdoor-side electronic circuits.
High-capacity electrolytic capacitors are used inside the outdoor unit controller (inverter). They retain an 
electrical charge (charging voltage DC 311 V) even after the power is turned OFF, and some time is required 
for the charge to dissipate.
Be careful not to touch any electrified parts before the control circuit board Power Lamp (red) turns OFF.
If the outdoor control circuit board is normal, approximately 180 seconds will be required for the charge to 
dissipate. However, allow at least 30 minutes for the charge to dissipate if it is thought there might be trouble 
with the outdoor control circuit board.
For example, if the outdoor control circuit board fuse has blown, approximately 30 minutes will be required to 
discharge the high-capacity electrolytic capacitors.
80