AC / demister not working after flat battery

My car’s been on a ship for the last two months and the battery obviously went flat. Initially we struggled to get it started until we jumped it directly from to the battery behind the seat. The front screen demister/AC now will not work. The comments from the technician are as follows :-

“The clutch on the air conditioning does not cut in. Air con gas pressure and amount is ok, A/C button operates but does not engage the clutch, All A/C fuses are ok, Re-circulate button operates. No fault codes come up on the OBD.”

If anybody has any ideas they would be much appreciated. Many thanks

It’s a 2007 Vantage v8 Roadster – UK spec