My a/c in my 2002 Silverado has a 5 setting switch. If I turn my a/c on 1 or 2, you can’t feel anything coming out and eventually it gets too hot in the truck. If I turn the switch to settings 3, 4, or 5, it works normal and the inside of the truck gets nice and chilly. Any idea what could be causing this? Would I just need to add more Dex cool?
does it only turn the fan on like this on AC, or does it do this on heat too?
check and get back with the info.
likely the blower resistor has schatt the bed. the usual thing is it loses the slowest speed first, then the next and so on. cheap fix the resister is about 100 bucks installed, but they only cost around 25 or 30 bucks if you can do it yourself.
the only glitch is the fan motor may be going, which eats up resistors. but for the cheap first thing to do replace the old resistor. then if it goes again you know the fan motor is dying.
That sure sounds like it is the fan speed switch. The same thing will happen if you switch on the heat. It is usually the slower speeds that go out first. High speed does not go out because it does not have a resistor.
Those resistors are not expensive, but they can be difficult to install. Since you have a truck, they are often easier to get to.
This can be a DIY project if you are comfortable doing this kinds of things.
No it has nothing to do with the coolant (Dexcool)
Edit: It is possible that the resistors are burning out because the fan motor is going out and is drawing more current than usual. If a replacement resistor burns out, plan on a new fan motor. I see Cappy also caught the same omission. 
Agree with the others that the resistor block is the prime suspect. You may be able to handle the replacement yourself if you can locate the bad part.
You are correct. The same thing happens when I put the heater on as well. Nothing until the third setting. Thanks for the input!
If you want to avoid changing the thing twice due to blower motor drag, you could put an ammeter on the blower motor. At the highest setting, it might draw pretty close to the fuse rating when spinning up, but drop way down to 1/2 or 1/3 of that when running.