I think it was because they were supposed to be all electric. Like the A/C is going to work in 117 degree heat!
There was whining about them being electric too. Which was really silly. USPS is a good candidate for electric vehicles. Routes are short, well within electric range, then they go and sit in the parking lot of the post office, easy to recharge. And knowing folks in Tucson with electric cars, AC works just fine.