Hi Drew - thanks for the answer. It is indeed the case that the top radiator hose is hot and the lower one is cool. Does this indicate that coolant is not circulating? The garage felt this was normal. Is that not in fact the case?
If the engine isn't actually overheating - where is the temperature gauge taking its information from and how is this related to the air con? Is there some kind of fail-safe cutting out the compressor?