AIRCON NOT COOLING
 

My aircon takes forever to cool down. Sometimes it never does. I did a trip of 100 KM recently and it only started to cool down after 50 km's. Does it need regassing or cld it be a blockage. How can i check without paying an arm and a leg to have someone else check???
Also what gas does the car use... 1999 A4 1.8T