Viessmann VITOCAL 250-A - Page 181

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A.93 Hot gas pressure not plausible
A.93
System characteristics
Refrigerant circuit operation impaired
Cause
Values for hot gas pressure in relation to hot gas tem-
perature not plausible
Measures
1. Check high pressure sensor:
With the system running, measure the voltage U
from 0 to 5 V at connection X14.2/X14.3 of the
VCMU refrigerant circuit controller.
If it deviates from the curve, replace the high pres-
sure sensor.
2. Check hot gas temperature sensor:
Check resistor R for NTC 10 kΩ on the disconnected
plug. Replace sensor if required.
Connection: X14.9/X14.10 on the VCMU refrigerant
circuit controller
A.94 Suction gas pressure not plausible
A.94
System characteristics
Refrigerant circuit operation impaired
Cause
Values for suction gas pressure in relation to suction
gas temperature not plausible
Measures
1. Check low pressure sensor:
With the system running, measure the voltage U
from 0 to 5 V at connection X14.5/X14.6 of the
VCMU refrigerant circuit controller.
If it deviates from the curve, replace the low pres-
sure sensor.
2. Check hot gas temperature sensor:
Check resistor R for NTC 10 kΩ on the disconnected
plug. Replace sensor if required.
Connection: X14.7/X14.8 on the VCMU refrigerant
circuit controller
A.96 Air in the secondary circuit
A.96
System characteristics
■
Unusual operating noise
■
Unusual starting and operational characteristics
Cause
Air in the secondary circuit
Measures
Vent the system. Top up with water if necessary.
A.99 Secondary circuit flow temperature too low
A.99
System characteristics
Refrigerant circuit temporarily off (condenser frost pro-
tection)
Cause
Flow temperature in the secondary circuit downstream
of the condenser too low
Measures
■
Check temperature sensors and flow sensor.
■
Check function of secondary pump/heating circuit
pump, heating/cooling circuit 1.
Messages
Warning messages (cont.)
6218234
Diagnosis