Sounds like yours is just from condensation, but mine actually cut out.
Here is an answer I got when I posted this question recently:

I agree with him for the most part. It's quite likely undercharged.
You might have a small leak. Mine never freezes, and I live in humid
capital USA.. IE: Houston.. It's so humid here, when I drive at
night all my windows fog up on the outside. Bad..
The only way an evap coil can freeze is if the coil temp drops
below freezing. That is usually due to either being low on
refrigerant,
or a possible restriction of the intake air, IE: clogged filter, or
too cool temps outside. Being it's summer, I'd cancel the last..
You might check the filter.. It's somewhere under the glove
box area. If it's not dirty, I'd have the system checked. It's
probably just a bit low on 134a.
MK

Hugh, what keeps the evap coil from freezing is the systems
controls cycling the compressor to keep the evaporator
the correct temperature.  That's why it cycles unlike building
comfort cooling (a/c) systems compressors that never
cycle off when in cooling mode.

I recently heard this same question on the PBS "Click & Clack" car show.
Their answer: Next oil change, ask your mechanic to use a thin piece of wire
to unclog the hose, which is probably clogged at the end with road gunk. Do
it before you end up with a mildew situation inside the car, or your next
question will be about the best form of suicide.

As far as the location of the drain hose, begin looking under the car
beneath the area just ahead of the glove box.

The drain hose can be difficult to find, but it is found along the top edge
of the carpet, at the firewall.

I doubt the hose is kinked, my experience was that carpet fibers had formed
a plug. It is easy to resolve this problem.

The hose is very similar to the miles of vacuum hoses that you find under
the hood.

You did not mention what kind of vehicle you have, but for Toyotas, the most
common cause of water dripping on the passenger side is the drain hose got
pulled out of the hole in the floorboard.  Pull back the forward edge of the
carpet under the drive's side of the dashboard and look for a hose about the
diameter of a pen.  The bottom of the hose should pass through a hole in the
floorboard but most likely, it got pulled out of the hole.

A common problem on other makes but less common on Toyotas is that the hose
gets clogged, which may be the case if the hose is properly routed through
the hole in the floor.  If the hose is clogged, stick a wire up from
underneath to free the clog.