Re: '02 Ford Exlporer LTD clicking (clunking) noise at rear of vehicle
The noise at the back might be the fan. It could have a bent blade. If it's similar to my Durango the fan blades are horizontal and tubular in shape to save space. Kids can wedge things in there such as candy wrappers and the like. It's best to take the cover/vent(s) off and have a look see.
Does the front A/C blow cold? I imagine both systems are connected (most are to save on costs). In any case, under the B pillar, normally on the passenger side, you'll see the A/C lines feeding upward. The best thing is to get under and have a look; knowingly, the seal to the one line is bad or has ruptured. This happened with my '00 Durango R/T a couple years ago. The solution was to replace the lines with a single, front A/C line only or pay the $3K or so to replace the rear line with condenser. I chose the $200 front A/C line. I took a photo of the A/C lines going up into the B pillar with the flash on.
By having the flash on and looking at the photos on a larger scale, you'll be looking for a glowing green fluid. If you see any, you've found your leak. I say 'glowing' because it's much more pronounced than if you went under the vehicle and tried to guess on what fluid was coming out or if it was underbody gunk, etc.
If you found a solution to this in the meantime do let us know.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!