06 Express van

I have a Chevy Express van for my work, I am in and out of it all day.
But I use the inside as an office, desk and all, I live in the Phoenix metro area (hot)
when I sit for any lengh of time, the temp guage climbs an the A/C slowly fades away.
I took to dealer for a solution with no luck, they say it is not designed to idle for periods
of time and keep the interior cool, well I am looking for help/ suggestions, there are several
other 06 Express vans in our "fleet" and some say they have the problem and others do not.
If I open the hood when idleing it appears to help sometimes, and others I am not sure, it
is really starting to heat up here in PHX, was wondering if a external electric fan would work
or help and if so, where do I get one and what type, or is there a better solution.
If the van starts to warm up and a/c starts too shut down sometimes I will rev the van up a
little and it will cool down, I cannot believe there is not a solution.
My last van was a winstar and it kept cool all the time at idle.
5.4? litre v8 auto, w/rear a/c
Bill

check your coolant level fill it up if its low