Just thought I'd share this tip. I recently sold my 55 plate A3 1.9TDI . The day before the sale my air-con packed up. The ECON lamp was on permanently and I was unable to select AUTO. I had the system gas pressure checked which was OK, then the aircon guy said the fault was possibly the pressure switch. I bought one (£14) on the day of the sale ripped off the front bumper left-hand access cover and worked through the gap. I've since found out you can use a crows-foot spanner from the top. Switch unscrews from a Schrader valve so you don't lose system pressure. New switch fitted , everything works again. Car sold that evening. Bought another A3 cos I like them.