Anyways, low side is reading 100 PSI after 5 minutes of truck on max A/C.

If the compressor isn't running, and low side is already at 100 PSI....... system is either overcharged, or, there is a bad switch somewhere, or, system is plugged.....

 

It's just reading pressure from the can. The low side switch needs to be jumped.

 

I would be more tempted to backtrace the wires, and see where power disappears..... more than likely one of the pressure switches though.....

 

Jumping the switch will tell you four things

1 there is most likely no wiring problem
2 the compressor is ok if it turns on
3 the system is low on 134a
4 or the switch is bad.

If the compressor turns on when the low side switch is jumped let it take that can. Remove the jumper and put the plug back on the switch. If the compressor cycles on and off, it's still low on 134a. Give it some more until it blows nice and cold and the compressor stops cycling. And please wear protective clothing, gloves and eye wear.

More than likely the evap core is shot, and this is all an exercise anyway.

 

Folowing the test procedures that was posted from the FSM will also determine if clutch is shot, allow for proper refrigerant charge, etc.....and do not overcharge (such as 100 psi on low side)....overcharged is as bad as overcharged. More is NOT always better!

 

I want to actually jump into this. I figured, since I'm stuck with this beast, and after 256k miles it doesn't want to die, might as well get the A/C working. I haven't run any tests, I am curious to run the jumper, which I assume is just like jumping a fuel pump relay. A quick how-to would be cool. I removed the clutch relay in the box near the fender. With the A/C on, the clutch kicks on and off when I plug the relay in and out, pretty much just pushing the relay in and out to see if that was bad. I got a new one, and it did the same thing. The clutch engages for a split second then disengages. I doubt my step dad ever messed with it. So, I assume that it could maybe just need charged?

 

Sounds like it there burnt.

 

a good rule of thumb we go buy is 40 degrees out of the vents is more then enough.