I spent a LONG time trying to figure this out. The reason it was s much trouble for me (and the people on here who helped me out) was because the air-con was misbehaving. If the E-Con light is on, Air-Con is off. If you can't tell the difference between the two then your air-con system is buggered.
Could need a simple re-gas, it could be the pressure switch (you better hope it's one of these two) or it could be the pump.