If it's been three years since you ran your aircon then I'd say for definite you need a re-gas.
Three years is about as long as the system should go before a re-gas anyway as the refrigerant will break down over time.
If the gas pressure is low the compressor clutch won't engage to protect the system.
It is recommended that the system is run every week to keep the seals and pump lubricated.
cheers stoney871, i will get it regased when i get back off me hols.
bit of luck the sun has gone in and i wont need it again for another six - seven years.