CITROEN C2 Handbook page 266

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 blown air temperature.
Aircon circuit diagnosis table
Symptom
Low pressure normal and high pressure
too high
Low pressure normal and high pression 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
260
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