Saturday, September 10, 2016

Air Freezeditioning

     Yesterday afternoon Tam and I were busy at various, divergent tasks.  She had been folding laundry in the basement and when she returned to the surface, she told me, "You might want to check that condensation leak all around the furnace...."

     Uh-oh.  The drain line from the drip pan under the A-coil* is ludicrously large for the amount of water: Roseholme Cottage is not a very large house.  "Was there water on the top of the furnace?" I was hoping not.  The furnace sits in a slightly-lower spot. Maybe it was just seepage from recent rain that hadn't evaporated.

     "I think so."

     Drat.  Damme.  Shit-oh-dear..

     Investigation found a little water on top of the furnace, dripping down the outside to the floor; there was condensation on the outside of the section of duct where the A-coil lives.  Frozen up?  Probably.  I killed the cooling, set the fan on continuous run, and used my wet/dry vac to force-drain the condensate line and pan. It's just a PVC pipe run to the the floor drain, so that's easy.  In a few hours, the A-coil enclosure was down to room temperature and I wasn't getting any more water, so I opened up the furnace.

     Either I missed the last filter change or the cats really stepped up their shedding: the filter was pretty well blocked.

     I put in a new filter and ran the system on air-only for as long as Tam and I could stand it -- quite late, really -- then put the cooling back on with a higher set point.  So far, so good, it's producing cool air in some volume, but I'm not going to push it until we get into the week and I can ring up our furnace guys to check refrigerant level.  The forecast is for cooler temperatures and lower humidity, so here's hoping....
* What's an A-coil and why do they call it that?  It's the inside-cold part of the cooling, where compressed gas from the compressor/heat exchanger outside expands and cools down as it does so, and then cools the air passing through the A-coil.  In a central air-conditioning system, it typically lives in the ductwork at the output of the furnace, downstream of the fan and heating element.  In order to get the maximum surface air to cool the air in the space available, the coil -- like a car radiator -- is usually arranged in two sections that form an inverted V or lambda in cross-section; or, in fact, an A shape.  They can get clogged and do need to be cleaned occasionally, but are fragile and often hard to get to.  They are one reason why your furnace has a filter -- and why you should change that filter more often than I did.  So where's the water come from?  It condenses on the A-coil just as it does on the outside of a cold glass.  It drips off, is caught in the condensate tray, and drains down a pipe (or in case of a window unit, it just drips) -- unless your fan is running too fast, in which case it gets blown off the coil into the output air and you've got trouble.  This stuff isn't as easy as it might look, nor as simple. 


Anonymous said...

"They can get clogged and do need to be cleaned occasionally, but are fragile and often hard to get to."

Yea, I found that out the hard way. First new house and the A/C was just *barely* keeping up. I had heard about those coils needing cleaning so I scampered off to Home De(s)pot for some coil-cleaning-goodies.

Better living through chemistry in hand, opened up the evaporator (A-coil) and got to cleaning. (Spray-spray-spray) Wow! This stuff is amazing! Dingy-gray oxidized aluminum now bright and shiny! Rinsed off thoroughly with fresh water, mopped up and put it all back together.

Me so smart! (Patting self on back).

Uhhhh... Wait a sec here... Why is there no cold air coming out the vents? It's starting to get hot in here...

Did I mention the A/C was just keeping up because it was August in Florida???

The coil cleaner was a Phosphoric acid cleaner. Phos acid is a fairly benign acid, as far as acids tend to go. It's edible, like glacial acedic acid (vinegar). (It's a flavoring agent in Coca-Cola, for cripe's sake!)

It etched a hole through the aluminum coil.

I got to sweat a few weeks until I could afford the $1700 for a new A/C.

Me not so smart. (As I am continually reminded of...)

B said...

these coil cleaners are safe...and work fairly well.

another posibility is to put a simple duty cycle timer and a relay in the power circuit (or the thermostat circuit) before the contactor for the compressor....say turn it off for 7 minutes out of every 40 or so to give the coil time to drain. I did this on a marginal installation once and solved the issue... Simple ic timer and a relay....

Roberta X said...

I'm managing it by raising the setpoint. So far, so good.

Anonymous said...

The coil cleaner was acid-based, acid was a primary ingredient on the label.

When applied on gray, oxidized aluminum, the aluminum turned shiny. That is what is known as a clue that dissolution was taking place.

If it was so safe, why did my Freon decide to escape within 1 hour of product application?

I stand by my original position, use those cleaners with caution, it could be a very expensive cleaning of your wallet along with the now clean coils...

Old NFO said...

Hope it's nothing major...

B said...


Indoor coil cleaner SDS: No phos acid.

Outdoor coil cleaner (don't use on aluminum!) SDS:

Apparently you didn't read the label?

wheelgun said...

I had a PVC drain line that stopped draining. It also drains the water from the humidifier in winter and the hard water did it in. A trip to the Big Box, and some fun with PVC and I was back in

I had similar problems in Florida, but in that case the drain line was a breeding ground for algae no matter what I did.

And don't discount the filter change. That will screw up a lot of stuff in an AC/furnace.

Andrew said...

Your filter can be nice and clean, and your system will still sweat and fill with water if your drain plug is clogged or restricted.

You should have, or put, some sort of access plug in your drain pipe. Where I live, you get a buildup of snotty mold in the pipes. You can also get bugs living in the pipe, or snakes. A solution is to put 1/4 cup of Clorox in the drainpipe to kill the snotty mold about 2-3 times a year.

But (there's always a but) make sure you don't put the Clorox directly into the drain pan or anywhere where it will directly touch your veins, else you will trash your system.