Viessmann Vitoclima 300-S Service Instructions For Contractors page 28

Troubleshooting
Diagnosis
(cont.)
Checking the essential components of the external unit, type
OD306H
Mains voltage
The mains voltage must be between
198 and 264 V~.
External fan
Start test mode (see page 31).
Check the voltage at the fan motor
supply cables:
Across the red and black core: 310 V
± 20 V
Compressor
The compressor operates with a
brush-less DC permanent magnet
motor.
Reversing valve
In heating mode, the voltage at the
reversing valve must be 220 V~.
Electronic expansion valve (EEV)
The voltage at the stepper motor of
the valve must be 12 V .
Checking the essential components of the external unit, type
OT307H
Refrigerant circuit
The refrigerant circuit can be checked
in test mode "Maintenance" (see
page 31). The system operates with
fixed settings.
28
Across the orange and black core:
15 V ± 1 V
Across the yellow and black core: 2 -
6 V
The three winding resistances must
be identical and be lower than
0.5 Ohm.
The EEV must be switched ON simul-
taneously with the external unit. It will
generate noise and vibrations.
To activate the "Maintenance" test
mode, select "tt" and then "ttC"
(cooling) or "ttH" (heating) at the pro-
gramming unit of the external unit.