Home A/C repair question

[chris snell]

OK, DWeb, I need your help. The air conditioning isn't working in my house and I have a wife that's 39 weeks pregnant. I have a call out for a repairman but there's a city-wide heat wave and it may be a few days before they can get here. Mama is unhappy and I'm wondering if this is something I can fix.

Here are the symptoms:

- outside compressor seems to be running, no problem there
- pipes from compressor to the blower feel cold
- blower fan (which is part of the furnace) is running
- the large ducting that comes out of the blower/furnace is shaking lightly, like it's blowing air through there
- no air comes out of the registers

It's almost like something like clogging up my ducts.

Right now I have the system shut down and the doors are open but our house is super-insulated and it tends to warm up every night as the daytime heat works its way through the walls.

Ideas?

 

[mbrummal]

Can you follow the duct work and see if something came loose?

Is there an air divider somewhere in the duct work that could have broken/gotten out of adjustment and block all of the airflow past it?

 

[D Chapman]

Just had the same thing happen.

First, check the air filter and make sure it's not dirty.

Second, as in my case, there is a "fire door" in the duct work near the air handler. There was a thin piece of lead that's designed to melt in case of a fire, and trap the fire so it does not spread further into your home. My lead piece broke from vibration and the fire door closed restricting the air flow.

I'm only assuming that these fire doors are also used in residential buildings also, but in my case it was at the office in a commercial building.

I guess another thing to check while you're there is if the copper pipes are frozen, or if the water pan below your air handler is full of water.

 

[wheelen disco]

The evaporator in the register is probably froze up, turn off the AC for awhile, and let it thaw.

 

[chris snell]

Hmmm...frozen evaporator sounds likely. I turned it on for a minute this morning and it blew, just not very hard. I'll let it thaw and try again tonight.

It seems odd to me that an evaporator would freeze up, here in Colorado with our 20% humidity.

 

[adriatic04]

Hmmm...frozen evaporator sounds likely. I turned it on for a minute this morning and it blew, just not very hard. I'll let it thaw and try again tonight.

It seems odd to me that an evaporator would freeze up, here in Colorado with our 20% humidity.

I had this happen two summers ago, was out of town and couldnt assess myself, but that is what it was.

I am in Denver right now, its like fucking India right now. I was walking to meetings downtown from my hotel in a sport coat and dying. Go get some fans for the lady :ack:

 

[Drillbit]

If its a frozen evaporator turn your fan from "auto" to "on", that will help keep it from freezing up. X2 on turn your system off and leave the fan on for a while to defrost it.

 

[Levi]

Chris, it sounds like your coil is frozen up which is usually caused by low refrigerant or a clogged filter. Sometimes a clogged coil if the filter isn't changed much or it has been ran without a filter. From your description I bet you are low since you said both refrigerant lines were cool, the little line should be hot and the big line should be cold. Usually there will be ice on your lines (either inside or out or both) when this happens. Depending on your coil box or duct work you may be able to open it up and look inside or maybe leave it open to thaw quicker. When I worked on ACs with my grandpa we would sometimes turn on the furnace to thaw the ice out but most of the time we just left it off and came back later in the day or the following day. If you have someone coming to look at it you will want to make sure it is thawed out or they won't be able to add a charge. Depending on how bad it is frozen up you might expect a little water around your furnace too.

Depending on your coil/system type it could also be an expansion valve.

 

[1MITCH1]

Where is your indoor unit located ? If its in the attic like mine, look for a secondary filter right in front of the evaporator,I had to get on a ladder . Its meant to be in place during construction of a new home to keep all the dust and debris out. Its supposed to be removed, mine wasn't and I found it 7 years later!

 

[chris snell]

So I pulled the filter out and it was pretty much clean. I put a new one in just to be safe but I don't think the filter is my problem.

I'll turn the fan on and maybe the furnace if I can stand it...lol...

 

[Drillbit]

no need for the furnace, if it's as hot as you say it is it should defrost with just the fan pretty quickly

 

[az_max]

If your system is low on refrigerant, it will ice over. I actually had to put a 60w light bulb in the air handler to melt the ice in my old house. The A/C guy couldn't make it for a week and I couldn't stand it without working a/c. There should be an access door on your air handler to check for ice.

 

[paxton]

Low coolant for sure. It's funny how that works, but easy to understand if you know the physics of it.

The more pressure you have, the higher the temperature, right? That's the way AC works. The system compresses the refrigerant gas with the compressor, then in liquid form, as it moves it through the evaporator coil, it turns back into a gas and fills that larger volume. It's under lower pressure since it's in that larger volume, which decreases the temperature. The fan blows air over the coil, which cools the moving air.

Well, when you're low on refrigerant, that expansion cycle leads to much lower temperatures, since there is less refrigerant per unit volume than if your refrigerant were full, and that lower temperature freezes up your system.

I'm sure there are holes in what I said, and DWebbers will come out of the woodwork to correct me but that's the gist of it.

Anyway, mine just did that this year. $1600 for new evaporator coil, which had a leak. We kept switching it on then off to try to avoid the icing, and we were able to survive until the parts came in and the guy (finally) made it out to change it.

 

[chris snell]

Thanks, paxton.

The fan has been running today and now it's blowing through the registers. I'm going to wait until tonight to turn the compressor on. Repairman is coming tomorrow. I hope that they will take the time to diagnose the issue properly.

 

[Blue]

Is your coil pierced? Didn't you just have a hailstorm? Call the homeowners insurance company if so. I got a new roof and new AC unit last year due to our massive hailstorm in October 2010. I had the same symptoms you have and turned out to be coil pierced by hail. $500 deductible, about $17k in work done to the house.

 

[Big Papa]

How old is your unit? Exact same thing happened to me 2 years ago in August. My wife was 8 months pregnant, and it was 93 degrees in our home. Our unit is about 9 years old, and the outside fan wouldn't turn, but you could feel air through the vents.

It was a blown capacitor. About a $40 part. Really easy to switch out on your outside fan unit. It looks like a silver can, and when it's blown the top part looks blown up.

 

[chris snell]

Fortunately, us being the vagabond military family that we are, we rent.

After a day with the fan blowing 90 degree air, I think the coil should be clean. I'm going to wait until just before bed and then set that bitch to 71.

 

[Butch]

Fortunately, us being the vagabond military family that we are, we rent.

I know exactly where you are coming from!

 

[ROVERT]

After a day with the fan blowing 90 degree air, I think the coil should be clean. I'm going to wait until just before bed and then set that bitch to 71.

I guess it might be too late now, but if you read this early enough, make sure you turn the unit off (leave the fan in the air handler/furnace on) so that it thaws out before he comes to fix it. If he gets there and it is a block of ice he won't be able to do much without defrosting it first. With a low charge, chances are the outside unit is frosting as well. If you look inside, the compressor and suction line (the bigger of the two copper lines) are probably nice and icy.

 

[paxton]

I guess it might be too late now, but if you read this early enough, make sure you turn the unit off (leave the fan in the air handler/furnace on) so that it thaws out before he comes to fix it. If he gets there and it is a block of ice he won't be able to do much without defrosting it first. With a low charge, chances are the outside unit is frosting as well. If you look inside, the compressor and suction line (the bigger of the two copper lines) are probably nice and icy.

That's a good point. He will probably have a sensor that helps him narrow down where the leak is. My guy ended up using our water hose to quickly defrost it.