Phoenix, Arizona has some of the highest mean temperatures in the United States. Despite the series being set there, NONE of supporting characters are shown wearing short pants and the cast often dresses as if they were in a more temperate climate even in the middle of summer.
The diner works using three waitresses all of whom start at the exact same time of day. If Mel's is open early for breakfast and stays open to serve dinner that means that all three waitresses work 10-12 hour days, at least SIX days out of the week.
Even for a 1970s restaurant those types of hours would be excessive. Yet none of the waitresses complain about it in more than a comedic fashion.
Alice is supposed to have ended up in Phoenix when her car breaks down driving from New Jersey to Monterrey, California.
Driving from New Jersey to Monterrey, California, there is no reason to be as far south as Arizona. The most likely route would be taking Interstate 80 all the way from New Jersey. which enters California north of Lake Tahoe, then transferring to southbound Interstate 5 in Sacramento.