Repairs to condensate leaks at ductless split-system air conditioners:

Diagnosis & repair of condensate leaks from a split system air conditioning system.

This article explains the common causes of water found dripping from the indoor half of a split system air conditioner or heat pump unit and offers repair suggestions matched to the AC unit leak cause.

Condensate leaks from a wall mounted air conditioner can cause costly building damage including mold contamination of wall cavities or other building areas.

This article series describes split system air conditioning & heat pump systems.

Diagnose & Fix Condensate Drips from the Indoor Air Handler of a Split System Air Conditioner

A split system or "ductless" air conditioning (or A/C & heat pump) system dispenses with duct work entirely, using a wall-mounted indoor evaporator/blower unit and a separate outside compressor/condenser (below left and right). In this split system air conditioning design, one compressor/condenser may serve multiple wall-mount indoor units.

Each of these indoor units must have a condensate drain that directs condensate, produced by cooling humid indoor air, to the outdoors.

Before it lost so much refrigerant that the split system air conditioner simply stopped cooling it had exhibited a different failure: condensate sometimes dripped out of the bottom of the unit into the occupied space where it was installed.

The white pipe in our photo at left is the outdoor termination of a condensate drain for the indoor wall-mounted half of a split system air conditioner.

We'd like all of the condensate produced by the air conditioner to empty at this point.

But sometimes instead we find condensate dripping from the indoor unit. At below left, the indoor AC unit periodically dripped water down the wall and into the room below.

At below we show the same unit with its cover on and then in a second photo the cover has been removed to permit inspection of the condensate drip tray, drain line opening, and perhaps to discover other causes of dripping water from the unit.

When a wall-mounted split system air conditioner drips water (actually air conditioner condensate) out onto the walls or floor below, there are the following most-likely causes, in order of probability:

1. Most likely: the condensate drain line has become clogged
2. Possible: the unit is not properly mounted on the wall and is tipped so that an internal condensate drip tray overflows and leaks rather than sending condensate down the drain line. This can happen if the wall-mounted unit has been moved partly off of its supporting wall-mount bracket or if the bracket itself was not well-secured to the wall.
3. Possible: the split system indoor air handler unit drips condensate into the room when an iced-up cooling coil melts and the melt-water overwhelms the condensate drain or drips past the condensate catch pan into the unit housing and out into the room.
   
   This problem will occur when the refrigerant charge is low or when the refrigerant metering device is not working properly.
   
   See FROST BUILD-UP on AIR CONDITIONER COILS
4. Possible: the split system refrigerant piping inside the wall mounted unit or the suction line leaving the unit is not properly insulated, allowing condensate to form on refrigerant piping in locations where it drips past the condensate catch pan and into the unit housing where it then leaks out into the room or down the wall below.

Watch out: condensate leaks that you don't see but that occur inside of a wall cavity can lead to wet insulation, costly mold damage, and over a longer time, structural rot or insect infestation damage.

While the AirServ technician worked outside to add R-22 refrigerant at the compressor/condenser unit we removed the cover of the inside unit and promptly observed that the wall mounted unit was connected to its mounting bracket only at one end.

It was in fact hanging lopsided so that condensate in the drip tray flowed away from rather than towards the condensate drain.

It was no surprise that this unit dripped onto the floors below.

It was possible that the dripping was worse previously due to an iced-over coil as this unit also had now lost its refrigerant charge.

And to be sure that we were not also leaving a clogged refrigerant line unattended, we borrowed the service tech's (kindly-loaned) CO2 gun and adapter to blast-out the condensate drain's discharge tube.

See CONDENSATE DRAIN CLEAN & DE-CLOG for more options for clearing a clogged HVACR condensate drain line.

There we commented that while we have found this CO2 condensate drain blaster a very helpful tool that will sometimes send a condensate drain obstruction out through the condensate drain system, in working on split system air conditioners whose condensate drain opening is difficult to access you may find that you cannot get the rubber condensate drain line plug securely in place.

Watch out: don't go blasting condensate drain lines without warning your partner working outside lest you startle someone and cause an injury.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-01-19 - by (mod) - If the adjacent wall has water damage how should it be properly repaired?

Ann

The proper repair for an interior wall depends on the wall materials as well as the extent of damage. For example if water leaked into a drywall surfaced cavity there is risk of both rot and mold contamination as well as wet insulation, all of which justify at the very least an invasive inspection of the wall cavity to see if demolition is needed.

Moldy drywall is cut out, the exposed surfaces cleaned, and then the leak cause must be repaired before the wall is restored.

On 2021-01-19 by Ann Griffin

If the adjacent wall has water damage how should it be properly repaired?

On 2019-08-18 - by (mod) -

Sandy

Thanks for sharing your opinion of ductless (split system) A/C systems.

There are millions of split system A/C and heat pump systems installed; properly installed and maintained they are a very effective and successful product.

And if you are seeing condensate leaks from your air conditioner or heat pump, that is certainly not a problem confined to ductless or split systems.

For example see CONDENSATE LEAKS

But I agree that if split system A/C is not properly installed you could have a condensate spillage problem.

On 2019-08-16 by Sandy

I would not have one of these ductless split air conditioners. I would have a puddle of water or more condensate on the wall, between the walls, and on
the floor in the room where it is installed. It could cause a real mess and do a lot of damage in my house.

On 2018-09-19 - by (mod) -

Scott

If the leak you are seeing is wet or water there are two common causes repair.

When is that the condensate drain from your unit has become clogged

The other is that the unit is not sloped properly on the wall in condensate in the tray is not flowing to the drain

Of course other possible causes but I'm giving you the two most likely

On 2018-09-18 by Scott

My mini split leaks down the wall from the back of the unit the only thing I can figure is where the line that goes through the wall warm air is coming in could this be the problem

On 2017-11-07 - by (mod) -

Ma,

I think you're talking about an air conditioning or heat pump system. An electrically-operated system like that is not burning a fossil fuel and would not be expected to be a soot source.

On 2017-11-06 by Ma

Will using a Mitsubishi air and Heating wall unit cause a sooty resude on items in your home when dirty

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Continue reading at CONDENSATE DRAIN CLEAN & DE-CLOG or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CONDENSATE HANDLING, HVAC - home
• SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
• SPLIT SYSTEM AC / HEAT PUMP REPAIRS
  • SPLIT SYSTEM AC REFRIGERANT LEAK RE-CHARGE
  • SPLIT SYSTEM AC CONDENSATE LEAK REPAIR
  • SPLIT SYSTEM AC MOLD CONTAMINATION REMOVAL

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