Coolant leaking onto driver side floor

I have a 2000 Dodge Durango V-8 5.2. I just had a new evaporator put installed. In about a week the air conditoner just sstopped working so I took it back in and the mechanic said it was plugged up. He said he fixed it. About week later I noticed that collant had leaked onto the driver side floor. I have taken the car back twice since then and it still isn't fixed. The mechanic said he can't find a leak but the coolant has to be leaking from somewhere. It seems to only leak when the car is being driven. It is still leaking and I will have to make another trip to the mechanic. Do you have any ideas? Could the mechanic have poked a hole into something while unplugging it? My husband just passed away a couple of months ago or he would be handling this. Needless to say I am clueless and so apparently is the mechanic.