Drooling A/C must be stopped.

July 19, 2007 5:57 PM

My A/C is making my furnace drool. A lot.

We live in a main-floor/basement apartment, and our landlord lives on the 2nd and 3rd floors. The furnace and hot water heater are in the basement in our apartment, and the central air unit is in front of the house.

We've been in the house over two years, but very recently we have noticed a lot of condensation running off the furnace when we operate the A/C. It doesn't just "sweat", it actually drips and pools on the concrete floor. This is a new development, and we're obviously worried about water damage in our basement.

As part of our central air setup, the landlord built an enclosure that contains the unit as part of our garbage enclosure -- let me tell you, it gets very hot under there. Doesn't A/C need lots of ventilation? Could the lack of exposure to allow ventilation be pushing the condensation inside into the cooler furnace area?

posted by mrmcsurly to home & garden (8 answers total)

Sounds like your furnace coil is icing. This is often caused by dirty evaporator coil. It can also be caused by a plugged evaporator drain.

Your condenser, the outside part, should be well ventilated. However insufficient ventilation will increase head pressures which will cause poor performance and not icing.
posted by Mitheral at 6:15 PM on July 19, 2007

I'm a little confused what's going on.

Typically, A/C units usually have two parts. One is the evaporator, which lives (usually) inside the house, as part of the furnace/blower. It's what cools the air actually inside the house.

There is another unit, which lives outside, called the condenser. This is the machine that makes a lot of noise, has a lot of coils in it, and usually produces a lot of hot air.

The latter one has coils that are HOT (or warm) and needs a lot of ventilation to dissipate the heat. There shouldn't be any water coming off of it, because it's hot, and heat doesn't cause condensation.

The evaporator, which is probably part of your furnace, is COLD, and can cause condensation if it's in an area of high humidity. It's normal and expected for an A/C unit to pull water out of the air as it runs, and they are usually plumbed in to a drain so the condensate can drain away.
posted by Kadin2048 at 6:16 PM on July 19, 2007

I should add: if you are getting water into your house/living space/floor from the evaporator (furnace), then you should get someone in to look at it, because something is amiss. It could be that the drain is clogged, or maybe the coils have frozen (as Mitheral suggests) or there could be some other issue.
posted by Kadin2048 at 6:17 PM on July 19, 2007

Can you post a picture? I am confused as well and think it would help.
posted by procrastination at 6:42 PM on July 19, 2007

There is usually a pump designed to pump away this condensation. Look for tubing coming out of the furnace plenum. Follow the tubing to a small box. This box will have an electrical plug. Make sure it's plugged in. Try shaking the box a bit too. There's a float valve inside that controls when the pump motor kicks in. Check that the tubing isn't plugged or kinked. There should be another tube coming out of the pump and running into a drain somewhere.
posted by cosmicbandito at 6:43 PM on July 19, 2007

I can think of two possibilities off the top of my head:

a)The evaporator drain is full of growies, causing whatever drip tray is present to overflow.
b)The furnace has a built-in humidifier unit and it is malfunctioning (ie stuck on or leaking).

however, your post implies that the condensation is on the outside of the furnace unit itself. if that is the case, then I have no idea.
posted by ArgentCorvid at 6:43 PM on July 19, 2007

Sounds like your furnace coil is icing. This is often caused by dirty evaporator coil. It can also be caused by a plugged evaporator drain.

Could also be low freon. I just had this happen, and the unit was 1.5 tons low. Letting the unit thaw and topping off the freon took care of things.

The important thing to note here is that *something* is wrong; the fact that this is new behavior is the tip-off. Your landlord needs to have someone professional come out and look at it.
posted by davejay at 10:43 PM on July 19, 2007

The condenser is certainly not well ventilated, but from the comments so far that's a separate (but serious) concern from my drooling furnace/blower.

We have now successfully engaged the landlord on the issue, and look forward to a professional resolution. Thanks everyone for the help.
posted by mrmcsurly at 5:39 PM on July 20, 2007