Are we sure it's a bad pressure/temperature sensor? Is there some other relay or maybe simply not enough refrigerant in the system to be compressed to the sort of temperatures needed for the fan to come on?

Are the two kinds of sensors visually very different?

i'm sorry, i didn't mean to hi-jack this thread but i just wanted to know, what is a REED VALVE? how does it work and what is it for on AC systems? where is it located at?

FWIW (not much)
my aux fan would not ever come on, until after I added 2 cans of 134A whereupon it now cycles
- I even bought a replacement fan switch thinking it was bad (another lesson)

If it were mine, I'd get an infrared thermometer and check it. Handy tool to have for other things.

Be sure to check the accuracy percent of the less expensive ones. They can vary by as much as 5%, which is enough to impact optimal adjustment.

Ok, I just put 1,600 highway miles on this beast from my trip down south, and here are a couple things I learned...

1) I have a big friggin leak in my AC system somewhere which I would like to diagnose in the near future because the refrigerant doesn't stay in the system long

2) when the system is filled with refrigerant, the AC works great and chills perfectly, although I hear some squeaky chatter from the compressor during idle after driving on the highway (3K+ rpm)

3) the aux fan DOES engage! either I didn't have enough refrigerant in the system before or the temps weren't high enough, but now that there's a "heat wave" on the East Coast, the aux fan engages at idle by itself...

I found that the fat rubber-coated hose on the suction side has a lot of bubbles in the rubber and even some tear. I read that this bubbling is often indicative of a bad hose... Does it mean I need to replace that one for sure?