To add to this... This initial answer really helped me out for my 2004 Jeep liberty. Let me add a few more details to "give back" to those who helped me out.
I had first taken off the bottom plastic shroud which sits straight up above the floor board
and down below and back under from the the glove box. This was where I was kinda being steered from book I was trying to use to do the replacement of the resistor.
Then I came in and googled and found this pointing me to take out the glove box... from there I saw the resistor mounted into the firewall so took out the two bolts and pulled out the resistor with the wiring harness still plugged in. Then the challenging part at that point was to get the harness unplugged from the resistor. As was mentioned below, it is "non-intuitive" as to how to do this. By flipping over the assembly, you will see a sliding red kind of "latch" which seems to hold the harness plugged into the resistor. I was able to stick a screw driver into the back of that (wiring harness side, not the resistor side) and push it towards the resistor. This seemed to "unlock" things but it still needed some pursuation to finally unplug it.
Also, I'd note that they suggest that you take the negative lead off the battery for this surgery so to prevent any air bag triggering as you are messing around in this area.
Hope this extra detail helps.
I just did this a few months ago. It was pretty basic. You need a new resistor board, first of all. I got mine on eBay for far less than the dealer would've charged. I think there are aftermarket manufacturers of these, so you shouldn't have to pay OEM costs. The resistor device is located behind the glovebox, mounted into the firewall. The glovebox should be fully removed, it will just be a major hindrance if it is left in place. It is fairly obvious where the resistor set is because there is a substantial wiring harness attached to it. This is where my description will get a bit vague because it was so long ago. There are essentially a couple screws/bolts holding the existing resistor unit in the firewall, and there is also some kind of fancy clipping mechanism on the wiring harness. These all need to be removed obviously, and installation is simply the reverse. I remember nearly breaking the harness locking device b/c it was so non-intuitive, but I also think I remember that the lock wasn't essential, i.e. the harness would probably stay connected regardless.
You need to replace blower motor resistor.
Blower motor resistors are generally found nearby the blower motor.
The Blower Motor Resistor Pack is defective. Replace it.
your blower resistor is going bad
If your blower is only working on the high setting its most likely the fan blower resistor that needs replacing, which is a cheap fix. I've had to replace the resistor on both my 98 Jeep Sport and my little 94 Mazda MX-3. As for the squealing I think its most likely your belt needs replacing or re-tightening, or it could be a worn bearing on the water pump.
It does not have a ballast resistor, those were used for ignition systems 30+ years ago. It does have a blower motor resistor that is located behind the glove box.It does not have a ballast resistor, those were used for ignition systems 30+ years ago. It does have a blower motor resistor that is located behind the glove box.
bad blower resistor
Check the resistor pack on or near the fan , it may have melted and needs to be replaced.
The resistor is behind the passenger strut in the fire wall. Remove the wire from the old resistor, pull out the old resistor (held in by clips in the device. Install the new unit and re-attache wire. The space is tight and should not take you more than 30 minutes. Replacement part runs around $13.00 at Advanced Auto parts. Just replace on my 1999 Dodge Grand Caravan Sport 3.3 Flex
Thermostat possibly stuck open or heater control valve broken. Now if you mean the blower motor has stopped working, check the fuse, blower motor itself, or the blower motor resistor pack.
replace the switch
replace the a/c compressor by a pulley kit