Why does it only start leaking coolant from firewall side of engine once in awhile not all the time

What is your question?

it leaks coolant and starts steaming from firewall side of engine once in awhile other times it is fine no visible leaks or evidence of a leak. And why dont it do it all the time? Also notice my ac canister and lines are cold and frosted when i dont have ac on and my controls are set to hot defrost

What makes this problem better or worse?

dont know

How long has your 2000 Nissan Quest had this problem?

just started a few weeks ago