CITROEN 2005 C4-XSARA-XSARA PICASSO BERLINGO Owner's Manual page 452

CHECKING THE EFFICIENCY OF THE AIR CONDITIONING SYSTEM
Principal problem
Abnormal levels of pressure
Air conditioning operating in
back-up mode
NOTE: In all cases, measure the excessive heating (SC) and the blow air temperature.
Aircon circuit diagnosis table
Symptom
Low pressure normal and high pressure too high
Low pressure normal and high pressure too low
Low pressure too high and high pressure normal
Low pressure too low and high pressure normal
Under cooling too weak
Under cooling excessive
446
Possible causes
Presence of air in the aircon circuit
Aircon pressostat defective
Evaporator sensor defective
Aircon pressure reducer jammed open
Filtering and drying cartridge saturated or
clogged
Aircon pressure reducer iced up
Lack of aircon fluid
Excess aircon fluid
Presence of air in the aircon circuit
Filtering and drying cartridge clogged