Although the liquid is probably coolant, it could be the aircon's refridgerant. When I had a leak on my AC system, I took it to my nissan dealer who regassed it and added some kind of green dye - the idea being it would be easier to detemine where the leak was coming from. The dye looked exactly like engine coolent...
if the leak only occurs sometimes, check to see if it only happens during/after using the AC...