I've never been a fan of the recirculate switch. I prefer to get fresh outside air into the cab rather than keep re-breathing the same air, though I understand if it is really hot then the aircon is going to work a lot harder trying to continually cool outside air.
The back wall of my cab has a pair of hidden vents and I guess the Bernoulli principal causes a partial vacuum behind the cab and sucks air out through these vents, which, with the aircon set to recirculate, sucks air in through door seals and other places.
Steve.
