Appendix
38
Installation and maintenance instructions geoTHERM 0020250180_00
Code Meaning
Cause
Remedy
F.735
Evaporation temperature too high
–
Temperature in the environment cir-
cuit (heating mode) or building cir-
cuit (cooling mode) too high for com-
pressor operation
–
Feed-in of external heat into the en-
vironment circuit
–
Reduce or stop the external heat
that is entering
–
Check the de-icer (does it heat
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 inlet
sensor and low-pressure sensor
F.740
Environment cir. inlet temperature too low
–
Inlet temperature in the environment
circuit too low for the compressor to
start
Heating:
–
VWS environment circuit inlet tem-
perature < -10 °C
–
Check the dimensioning of the
environment circuit for VWS
–
Check the sensors
F.741
Building circuit inlet Return temperature too
low
–
Return temperature in the building
circuit too low for the compressor to
start
Heating:
–
Return temperature < 5 °C
Cooling:
–
Return temperature < 7 °C
–
Check the sensors
–
Checking the cooling mixer
F.742
Environment cir. inlet temperature too high
–
Inlet temperature in the environment
circuit too high for the compressor to
start
Heating:
–
Environment circuit inlet temp. > 25
°C
–
Check the environment circuit
–
Check the sensors
–
Checking the environment circuit
pump
–
Checking the cooling mixer
–
Checking the isolation valve
in the environment circuit (if
present)
F.743
Building circuit inlet Return temperature too
high
–
Return temperature in the building
circuit too high for the compressor to
start
Heating:
–
Return temperature > 55 °C
Cooling:
–
Return temperature > 35 °C
–
Check the sensors
–
Checking the heating pump
–
Checking the non-return flap (if
present)
–
Checking the 2-zone set (if
present)
F
Sensor characteristics for the VR 10 external temperature sensor
Temperature (°C)
Resistance (ohms)
-40
87879
-35
63774
-30
46747
-25
34599
-20
25848
-15
19484
-10
14814
-5
11358
0
8778
5
6836
10
5363
15
4238
20
3372
