We just got back from Palm Desert. Took the tramway for a great hike on a day when it was 99 degrees in the desert. 3 days later, we took the tramway again. This time the desert was 116 degrees. We had no problem on the way up the steep road to the bottom of the tram. (There are signs telling you to turn off your air.) On the way down, there were no signs, but there should have been. We blew out the radiator, which left us stranded for several days while the car was repaired.
So, if you take the tramway road, keep your air off both up the hill and back down. And apparently, you're also supposed to put the car in low gear on the way down to reduce stress on the brakes.
Last bit of advice. If you do break down, keep an eye on the area. We ended up in a very sketchy part of town while we waited for a tow -- which thankfully came before sundown.