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Code/meaning
F.734
Condensation temperature too
low
F.735
Evaporation temperature too
high
F.737
The condensation temperature
in the refrigerant circuit is too
high.
F.753
The communication with the
frequency inverter has been
interrupted.
F.755
The 4-port diverter valve is not
in the expected position.
F.757
The heat pump has fallen below
the minimum compressor run-
ning time too often.
F.785
Environment circuit fan 2 is
blocked
F.788
Building circuit pump reports
internal faults
F.817
The compressor motor or the
connection cable is defective.
8000017440_FT Installation and maintenance instructions
Possible cause
The temperature in the heating
circuit is too low; outside of the
operating characteristics. Refri-
gerant volume too low
Temperature in the environment
circuit (heating mode) or build-
ing circuit (cooling mode) too
high for compressor operation.
Feed-in of external heat into the
environment circuit too high due
to increased fan speed.
Temperature in the environment
circuit (cooling mode) or build-
ing circuit (heating mode) too
high for compressor operation.
Feed-in of external heat in the
building circuit. Refrigerant cir-
cuit overfilled. Insufficient flow
rate in the building circuit.
Missing communication
between the frequency con-
verter and the outdoor unit's
control PCB.
Incorrect position of the 4-port
diverter valve. If, in heating
mode, the flow temperature is
lower than the return temperat-
ure in the building circuit. The
temperature sensor in the EEV
environment circuit displays an
incorrect temperature.
The compressor stopped sev-
eral times before the minimum
running time was reached. The
product was therefore blocked.
In systems without buffers and
with a low volume of heating
water, the temperature can rise
or fall extremely quickly when
the compressor starts. Depend-
ing on the start conditions, there
is a risk that the product will
stop.
There is no confirmation signal
stating that the fan is rotating.
The electronics of the high-ef-
ficiency pump has detected a
fault (e. g. dry running, block-
age, overvoltage, undervoltage)
and switched off the pump as a
securing measure.
Defect in the compressor (e.g.
short circuit). Defect in the fre-
quency converter. Connection
cable to the compressor is de-
fective or loose.
Measure
1.
Check the EEV (does the EEV move to the limit stop? Use
the sensor/actuator test).
2.
Check the compressor inlet sensor.
3.
Check the refrigerant filling volume (see technical data).
4.
Check the high-pressure sensor.
5.
Check the pressure sensor in the heating circuit.
1.
Check the system temperatures.
2.
Check the refrigerant filling volume for overfilling.
3.
Check the EEV (does the EEV move to the limit stop? Use
the sensor/actuator test).
4.
Check the sensor for the evaporation temperature
(depending on the position of the 4-port diverter valve).
5.
Check the volume flow in cooling mode.
6.
Check the air volume flow in heating mode.
1.
Reduce or stop the transfer of heat from outside.
2.
Check the back-up heater (heats up even though it is off in
the sensor/actuator test?).
3.
Check the EEV (does the EEV move to the limit stop? Use
the sensor/actuator test).
4.
Check the compressor outlet sensor, condenser outlet tem-
perature sensor (TT135) and high-pressure sensor.
5.
Check the refrigerant filling volume for overfilling.
6.
Check whether the service valves on the outdoor unit are
open.
7.
Check the air volume flow in cooling mode for sufficient flow
rate.
8.
Check the heating pump.
1.
Check the integrity of the wiring harness and plug connec-
tion and, if required, replace them.
2.
Check the frequency converter by actuating the compressor
safety relay.
3.
Read the assigned parameters for the frequency converter
and check whether values are displayed.
1.
Check the 4-port diverter valve (is an audible switching
available? Use the sensor/actuator test).
2.
Check that the coil is positioned correctly on the 4-port di-
verter valve.
3.
Check the wiring harness and plug connections.
4.
Check the temperature sensor in the EEV environment cir-
cuit.
1.
Check the circulation hot water volume.
2.
If required, increase the circulation hot water volume.
▶
Check the air route and, if required, remove any blockages.
1.
Switch the heat pump off for at least 30 seconds (no cur-
rent).
2.
Check the plug contact on the PCB.
3.
Check that the pump is working correctly.
4.
Check the building circuit (water volume, purging).
1.
Measure the winding resistance in the compressor.
2.
Measure the frequency converter output between the three
phases (it must be > 1 kΩ).
3.
Check the wiring harness and plug connections.
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