Water leak from drainage pipe?


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Old 07-25-08, 08:19 AM
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Water leak from drainage pipe?

Hello.

I have a central air unit. The furnace and coil are inside a closet in my upstairs hall. The unit recently started dripping a LOT of water (i.e. soaked carpet, pad and floor over night). We blew out the drainage pipe (the pvc that goes into the unit and then comes out outside) with an air compressor. When we did a big pile of goopy stuff came out and a large volume of water (this came out outside at the end). That seemed to resolve the issue for just over day. Now it is leaking again. Seems to come from the corner of the top part of the furnace and runs down the PVC pipe.

We just replaced the filter. And, like I said, blew out the drainage line (if that is what it is called).

We are about to call the AC guy but wanted to see if anyone had any other suggestions before we do so.

Thanks!
 
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Old 07-25-08, 09:50 AM
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Last edited by Michael Thomas; 07-25-08 at 11:00 AM.
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Old 07-25-08, 10:28 AM
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One likely cause:

Typically a standalone air handler, or the air conditioner evaporator coil on top of a furnace, has a pan located an inch or so below the bottom of the evaporator coil to catch the condensed water dripping off the coil.

Typically this pan has two drain outlets.

One, called the primary drain, is located on the side of the pan near the bottom. Water attempting to leave the pan will first attempt at exit via this drain.

If the primary condensate drain becomes obstructed, condensate will rise in the pan until it reaches a level of the secondary drain, which is located higher up on the pan's wall.

When the water reaches the level of the secondary drain, water will exit the pan through the secondary drain's condensate plumbing.

Sometimes, HVAC installers will leave the secondary drain plugged. This is contrary to most manufacturers installation instructions, nevertheless this technique remains common.

If the primary drain clogs, and the secondary drain is plugged, water will overflow the top of the pan under the evaporator coil and then run down the inside of the furnace or air handler and onto the surface below and perhaps into areas on floors below:



Cleaning out the portions of the primary drain accessible from outside the furnace or air handler will not always unclog it, as the clog may be in the pan under the evaporator coil or at its connection to the condensate drain plumbing.

There are several better condensate drainage installations possible, depending on local codes and requirements.

One possibility is to plumb the secondary condensate drain to an approved location such as above window, were the occupants of the building can be expected to notice if the primary plugs in the secondary begins draining.

A second is to install a pan under the air handler or furnace to catch condensate overflowing the primary drain, with a float or other kind of switch which will automatically shut down the air conditioning if the primary becomes obstructed and the secondary is already plugged and water runs down to the furnace or air handler into the pan:



A third is to install a switch at the secondary drain's exit from the furnace or air handler, and connected so is to shut down the furnace or air handler if the primary drain becomes obstructed and water reaches the level of the secondary condensate drain.

The link below shows the third installation at an evaporator coil above a furnace: the higher secondary drain to the left is equipped with a cutoff switch, the lower primary drain to the right is plumbed to a indirect waste receptor or other approved location. If the primary clogs and water rises to the level of the secondary drain, water running from the drain and into the switch will shut down the air conditioner until it is serviced.

Cutoff switch on air conditioner secondary condensate drain - Paragon Home Inspections Chicago/Evanston IL
 

Last edited by Michael Thomas; 07-25-08 at 10:54 AM.
 

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