Appendix
32 Installation instructions Heat pump control interface module 0020291573_00
Code Meaning Cause
Remedy
F.735 Evaporation temperature too high – Temperature in the environment
circuit (heating mode) or building
circuit (cooling mode) too high for
compressor operation
– Feed-in of external heat into the
environment circuit due to increased
fan speed
– Check the system temperatures
– Check the refrigerant filling volume
for overfilling
– Check the EEV (does the EEV
move to the limit stop? Use
sensor/actuator test)
– Check the sensor for the evaporation
temperature (depending on the
position of the 4-port diverter valve)
– Check the volume flow in cooling
mode
– Check the air volume flow in heating
mode
F.737 Condensation temperature too
high
– Temperature in the environment
circuit (cooling mode) or building
circuit (heating mode) too high for
compressor operation
– Feed-in of external heat into the
building circuit
– Refrigerant circuit overfilled
– Insufficient flow rate in the building
circuit
– Reduce or stop the external heat
that is entering
– Check the back-up heater (heats
up even though it is off in the
sensor/actuator test?)
– Check the EEV (does the EEV
move to the limit stop? Use the
sensor/actuator test)
– Check the compressor outlet sensor,
compressor outlet temperature
sensor (TT135) and high-pressure
sensor
– Check the refrigerant filling volume
for overfilling
– Check whether the service valves on
the outdoor unit are open.
– Check the air volume flow in cooling
mode for sufficient flow rate
– Checking the heating pump
– Check the building circuit flow rate
F.741 Building circuit: Return temp. too
low
– During the de-icing, the return tem-
perature falls below 13 °C
– Ensure the minimum installation
volume is maintained; if required,
install a series return cylinder
– The fault message is displayed until
the return temperature increases to
above 20 °C.
– Activate the electric back-up heater
in the product's control panel and
in the system control in order to
increase the return temperature. The
compressor is blocked while the fault
message is present.
F.752 Fault: Frequency converter – Internal electronics fault on the in-
verter PCB
– Mains voltage outside of 70 V–282 V
– Check the integrity of the power sup-
ply cables and compressor connec-
tion cables
The plugs must audibly click into
place.
– Check the cable
– Check the mains voltage
The mains voltage must be between
195 V and 253 V.
– Check the phases
– Replace the frequency converter, if
required
F.753 Connection fault: Freq. conv.
n.recogn.
– Missing communication between the
frequency converter and the outdoor
unit's control PCB
– Check the integrity of the cable
harness and plug connection and,
if required, replace them
– Check the frequency converter by
actuating the compressor safety
relay
– Read the assigned parameters for
the frequency converter and check
whether values are displayed
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