Mk1 Focus TDCI Aircon (UK)

My 52 reg 1.8 TDCi Focus has been sat unused for a month while I've been on

holiday.

Having driven it today for the first time since, it seems the Aircon isnt 
working at all.

i.e the blower works, the Aircon light comes on with the switch, but no
cold 
air.

Selecting re-circ doesnt make any difference.

Its been very cold around here in the last few weeks - not sure if this
may 
be a factor.

Are there any DIY actions I can take, or am I off to see the Aircon man??

TIA

Andy