UK Car Repair Questions? Ask a Mechanic for Answers ASAP
That is likely the freon leaking out of the system. Your A/C evaporator is mounted inside the air box, so if it ruptures the freon escapes into the airbox. Sometimes you will get a little water dripping from the evaporator if your A/C drain under the car is plugged, but the only thing pressurized is the freon.