Mini Split Air Conditioner Leaking from the Indoor Unit.

June 16, 2010 by Shawn Mack  
Filed under Ask Thomas

First Name:  Eric

Last Initial:  B

Equipment:  Mitsubishi Mini Split Air Conditioner


The mini split AC unit cools beautifully.  However, anytime we set the temperature below 70 degrees, we will get water dripping from the inside unit.  This is not condensation water dripping from the vents - it is water coming out from the unit.  This unit does have a drain tube to the outside and it does work properly.  Could this water problem simply be a result of the drainage tube freezing?  If so, is there a solution.  It defeats the purpose of the AC unit if you cannot make it cool in the house.  Any responses are appreciated.


There are two possible solutions to prevent leaking from a mini split air conditioner indoor unit.  One:  There is a blockage in the drain line or the drain line is not installed properly and gravity cannot rid the system of the condensation build up.  Two:  The drain pan inside the indoor unit is level and water cannot drain, via gravity, out the back of the system and down the drain line.  Most units will need to be installed with a slight declination towards the drain line side.  This lets the water flow downward and out of your conditioned area.  People see leaking indoor units on very humid days when the drain pan fills more quickly and cannot terminate the water fast enough because of the drain pan being level.  I tell my customers to tilt the indoor system 1/8″ down towards the drain line at the time of installation.