Viessmann Vitoclima 300-S Service Instructions For Contractors page 30

Troubleshooting
Diagnosis
(cont.)
Reversing valve
The reversing valve comprises an
electromagnet and the valve itself.
In heating mode, check the voltage
across both connections of the rever-
sing valve. The standard voltage is
230 V~.
Electronic expansion valve (EEV)
The EEV comprises a drive (stepper
motor) and the valve itself.
The EEV must be switched ON simul-
taneously with the external unit. It will
generate noise and vibrations.
The voltage at the stepper motor of
the valve must be 12 V .
To ensure that the EEV is responsible,
implement an installation test (see
page 14).
Temperature sensors
Check connections and connecting
cables.
Communication between the internal device and the external unit
Switch the system OFF and then ON
again. If the fault persists, check
resistances of the communication
cables and earth. The resistance
should be lower than 2
Electromagnetic faults
The following faults can occur near
transmitter stations, amateur radio
stations, sewing machines and arc
welders:
30
If there is no voltage, check the elec-
tromagnet with a direct power supply.
If OK, replace the controller.
If the electromagnet and the controller
are OK, and the compressor runs but
there is no heating, replace the valve.
Should this test fail and the diagnosis
result in no further findings, then the
EEV is faulty.
If the stepper motor is OK (see above)
and the internal device still delivers
no cooling, replace the valve. It is not
necessary to drain the refrigerant.
Charge the external unit with refriger-
ant (see page 15).
At a temperature of 0 to 40 °C, the
sensor resistance should be between
35 and 5 k .
If the fault persists, replace the con-
troller of the internal device or the
external unit, subject to the type of
fault.
.
During operation, the equipment
suddenly switches itself OFF.
LEDs flicker.
Use suppression cables or remove
the source of the interference.