Leaky Air Conditioner

[lscheck]

I came home the other night and found water leaking from the condensate pan in my central air unit. The pan was full and it appeared that the gravity drain line (PVC) was clogged.

There is no removeable fitting so I cut the PVC in the middle to find the blockage. The place I cut must have been upstream of the blockage because all the water drained when I cut it. I then removed the downstream section of pipe and snaked it out. It didn't appear very dirty and I was surprised that it was blocked.

I then discovered that someone had placed a box in front of the intake grille for the unit- effectively blocking most of the air intake.

So here is the question- Is it possible that blocking the intake to the unit caused a vacuum and prevented the condensate from draining - thereby causing the pan to overflow??

LarryS.

[LazyPup]

It depends on the physical layout of your hvac unit. If the evaportor is on the intake side of the blower, blocking the airflow will produce a slight negative air pressure that in some cases will effect the condensate drain line. When i install a unit with the evaporator on the intake side of the fan i often install a tee on the condensate line with the side opening connected to the unit and a short vertical stub that is left open as a vent for the drain. It also leaves an opening where a plumbers wire snake can be passed through the drain line to clean it.

Whenever i service a unit i make it a point to run a wire snake through the condensate drain line before I clean the coils to insure the line is open to drain the cleaner and water from the evaporator.

You want to caution everyone in the house about the potential for blocking your return air. Blocking return air will cause the evaporator to super cool and will result in ice forming on the evaporator.

In a worst case scenario once the evaporator is iced over the liquid refrigerant will flood over and down the suction line back to the compressor. You would see ice forming on the suction line and even on the top of the compressor housing. That is a very dangerous condition because liquid refrigerant entering the compressor can damage the intake valves which would require changing the compressor.

If you see ice forming or suspect ice on the evaporator coils turn the AC off and turn the fan on manual, That will stop the cooling process but continue to circulate the warm room air through the unit to defrost it.

[lscheck]

Thanks for the feedback.
I just checked and the evaporator is on the outflow side of the fan- so I guess my vacuum theory isn't working. The pan seems to be draining now- so I am still not sure what the cause of the blockage was.

I like the idea of putting in a piece with a vertical piece that I can uncover as a cleanout. Not sure if someone makes a clear piece rigid PVC like this- so anyone could quickly check to see if the water is flowing properly.

Regarding the damage that a blocked intake can cause- I understand this and might have to post a sign on the wall by the intake about not storing things there.

[HayZee518]

Ischeck - Lazypup is a man beyond his times. All his input to problems is from a common sense viewpoint. He has ALL the knowledge of the trade and a lot that overlaps the different fields. He has degrees that I can only hope for. Good man - listen to what he says.

[LazyPup]

There is a gelatinous mass that often developes in condenstate trays and drain lines. You stated that you had snaked the line, probably when you snaked it, the obstruction was washed out by the water standing in the line and you didnt see it.

You can get some slow dissolving chlorine tablets called "pan Tabs" at most HVAC suppy houses that will help prevent the algae from forming in the pan. You simply drop a couple of the tablets in the pan when you change your filter.

[lscheck]

I have been watching the drain line for a week and the condensate seems to be flowing.

Your comment about the "gelatinoius mass" makes sense. When I snaked out the line I saw some "gel stuff" come out the far end. I didn't think it was enough for a blockage but this does seem like the most likely situation.

Good forum- thanks for all the help.
LarryS.

[LazyPup]

In most cases it takes very little of that gelatinous gunk to clog the line. A mass the size of your thumb would be sufficient to block the line. If that gunk should happen to remain in the line at the end of your cooling season it will dry out and form a semi hard crust that almost looks like a thin yellow piece of plastic.

In a worst case scenario if that stuff is allowed to continue growing it can coat the surface of the evaporator and would then require an HVAC tech to open the system up and manually clean it with a chemical coil cleaner and a fin comb, a very, very messy, and usually costly job.

This is one of those cases where an ounce of prevention is certainly worth a ton of cure.

You could occasionally shut the AC off for about 8 hours and put some laundry bleach in the condensate tray to kill the bacteria that causes the growth, but not many people are willing to sacrifice the air in mid season.

The easiest, and best method to prevent that growth is to get a supply of PAN TABS. There are tablets of a chorine type antibacteria that slowly dissolve and continually treat the water in the tray to prevent algae growth.

You only have to drop one or two tablets in the pan about once a month when you change the air filter.

Generally they are packaged for HVAC contractors in a pint or quart size plastic bottle, and one pint bottle of the tablets would be an ample supply for two or three seasons.

There are some that are packaged six tablets in a plastic sleeve. The sleeve has holes and they say you can just drop the whole package in the pan. I have used those in the past but found that sometimes after the tablets dissolve the empty pack will float over against the drain opening and cause a clog.

It is economical for a homeowner to buy then in that type of a package but i would reccomend you open the package and drop the tablets in the pan loose.

You can buy Pan Tabs at any HVAC supply house, and occassionally you can find them in Home Depot or Lowes. It would probably cost less than $10 to get a years supply of them, which is certainly cheaper than paying someone to clean your system or even rent a carpet shampooer to clean the excess water out of your carpets.