121
F.772 Lead break, compressor oil sump temperature sensor
F.772
System characteristics
Refrigerant circuit operates only when outside temper-
atures are > 5 °C
Cause
Lead break, oil sump temperature sensor
Measures
1. Check connection X20.3/X20.4 on the VCMU refrig-
erant circuit controller:
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
2. Check resistor R for NTC 10 kΩ on the disconnected
plug. If R > 300 kΩ, replace the sensor.
3. Replace VCMU refrigerant circuit controller.
F.773 Short circuit, compressor oil sump temperature sensor
F.773
System characteristics
Refrigerant circuit operates only when outside temper-
atures are > 5 °C
Cause
Short circuit, oil sump temperature sensor
Measures
1. Check the sensor and connection X20.3/X20.4 on
the VCMU refrigerant circuit controller:
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
2. Check resistor R for NTC 10 kΩ on the disconnected
plug. If R < 500 Ω, replace the sensor.
3. Replace VCMU refrigerant circuit controller.
F.788 Lead break, 4/3-way valve
F.788
System characteristics
■
No room heating/cooling
■
No DHW heating
Cause
Fault, control and/or power supply of 4/3-way valve
Measures
1. Check connections X1.1 to X1.5 on the EHCU elec-
tronics module.
■
Check wires and plugs for correct seating.
■
Check connections for contact corrosion.
■
Check cables for mechanical damage, e.g. crush-
ing, kinking, chafing or breakage.
Replace connecting cable if necessary.
2. Check voltage U between X1.2 and X1.4 on
EHCU electronics module:
■
If U = 24 V , replace 4/3-way valve motor.
■
No voltage: Replace EHCU electronics module.
F.790 Mechanical fault, 4/3-way valve
F.790
System characteristics
■
No room heating/cooling
■
No DHW heating
Cause
Mechanical fault on 4/3-way valve, e.g. damaged valve
finger or break in guide shaft
Messages
Fault messages (cont.)
6218234
Diagnosis
To Next Page