Hello, last year I had my air conditioner filled. After a solved contact problem, it runs now as well. At least the compressor plugs in. However, it does not cool. In the interior a hissing is heard during operation. Otherwise nothing happens. According to the workshop the system is dense and the coolant quantity should also be correct. Can the evaporator be added so that there is no more air or there are other reasons? It is a manual system. Should one have been for retrofitting. The pressure switch is at the front of the cooler with this model. Also looks a bit puffed in overall.