is it normal for water to drain heavy if the car sitting with the AC on?

Yes. This is an indication the air conditioning system is working properly. The Freon in the system expands into a gas form and becomes icy cold, this is why it feels good, and then it is compressed back into liquid form so the cycle can be repeated without the need of continually adding Freon. Condensation builds around the cold components and drips onto the ground. This is normal. http://www.freeautomechanic.com/airconditioning.html