Domestic air con unit

I have a 2014 Dorset with a domestic roof mounted air con unit which does not blow out any cold air just only seems to re circulate the air in the van does anyone know if you need to
Get them re gassed like a car or are thay just nit very efficient ?
Mike

It's Dometic not Domestic and if you Google Dometic Air Conditioning you can download the manual if you haven't got one.

Hi Waky. I have the same Dometic unit on my Dorset and it seemed to me to simply recirculate ambient air. However, I've just been told that the aircon only works if the ambient temperature is high and the heating element only works if the ambient temperature s low. I tried it on a warm day last week and certainly the air output seemed cooler than ambient but it took 10 minutes to get cool. 
I found the manual to be slightly less than helpful.
Cheers
John