Re: How to defog windshield when A/C doesn't work..
You are getting plenty of air blowing though the defroster vents right?
When our AC compressor went on our WJ, it would still defrost just fine. Hot weather was the problem.
A very small leak will probably not make the carpet wet, but will be enough to fog windows. You may or may not smell the antifreeze. You may or may not notice any changes in the coolant level.
I think you could try a bit of pepper or stop leak in the coolant to see if that will stop the leak temporarily, perhaps long enough to isolate the issue to the heater core.
Otherwise a radiator shop can do a pressure test, which involves removing the core, putting it under water and fill it full of air similar to checking for a tire leak. Since its a PITA to get at the WJ heater core (I think you have to take the heater housing out which means taking the dash apart) most radiator shops will just replace the core with a new one and be done with it.
If you didn't need the heat, or for a test, you could just bypass the heater core by rerouting the hoses within the engine compartment.
2011 WK2 Overland Mineral Gray/Black, Advanced warning, V8; 2009 KK Rocky Mtn V6; 2000 WJ Laredo I6; 1979 CJ7 I6... green... miles of smiles :)