I am a first-time homeowner as of last fall, and my new home features central air, which is a totally new, luxurious experience for me (my previous AC experience is limited to window units). It’s certainly been a godsend during several of the hottest days of this year, but it definitely doesn’t seem to be running as efficiently as it should be. And it’s let us down bigtime on a couple of the real scorchers.
Half the time, it’s great: keeps the whole place cool and comfortable several days at a time. It can certainly take its sweet time getting there–especially if it’s particularly hot outside–but doesn’t seem to have any problem getting the inside temperature down to a pleasant 75F or so within an hour or two, even starting from 85-90F. Other times, it will start out fine, with a few hours of appropriately cold air coming out of the vents, but then seems to fade as the day goes on and doesn’t even recover when the sun goes down and it starts to cool down a bit outside (at which point we will give up on it and open windows instead).
Before I call a technician to come in and take a look, I was wondering if there were troubleshooting or maintenance tips for things that I could check myself. Or at the very least, I’d like to be a little more well-informed about the various potential issues before I’m talking to someone.
The Basics:
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[li]The house is in the suburbs of Boston and is about 100 years old, but the Central Air was installed during renovations immidiately prior to us purchasing. The whole system (including the air handler and vents) are somewhere in the 1.5 year old range. The air system is separate from the heating (forced hot water radiators) except that they share a thermostat upstairs.[/li][li]About the thermostat situation… it’s a bit odd in that there is a thermostat upstairs (that it shares with the upstairs heat) and downstairs (which is just for AC; there’s a separate thermostat altogether for downstairs heat). Either seems capable of activating the system, even if the other is Off. I don’t know why there are two, exactly, because while the heating has separate zones for each floor, the cooling does not.[/li][li]I replaced the filter most recently about a week ago. Air flow doesn’t seem to be a problem–it’s just that the air that’s flowing doesn’t seem to be as cool as expected at times.[/li][li]It always starts out strong, with several hours of cold air. Sometimes it’s fine for days at a time, sometimes the air that’s coming out gets less and less cool as time goes on.[/li][li]When it fades, it’s always been in the afternoon (when it’s hottest), but some very hot afternoons it’s fine. And as noted earlier, once it’s crapped out it doesn’t seem to recover–even if the outside temp drops. But if left off overnight, it will be fine the next morning again.[/li][li]When it’s working well, I notice that the outside fan/compressor unit stays on for quite a while (10 minutes? maybe more?) then off again for a while. When it’s working poorly, the fan/compressor is cycling on and off very rapidly: less than a minute on then off.[/li][/ul]
Besides the filter, is there anything I else could check? Any testing that I should do before calling someone? Likely culprits for the cause?
Next time it craps out, flip the AC to off (either by raising the temp really high or switching the Cool/off/heat switch to off) AND turn fan switch from AUTO to ON. Let it run like that for an hour or so and then change it back and see if you get cold air again.
I have a hunch your coils are icing up and this’ll defrost them. It could be for one of several reasons which we can discuss later, but let’s start by testing the hypothesis.
If you’re handy with tools, there should be an access cover near the air handler that you can pop off or (usually with some zip screws) and take a look at the evaporator with your own eyes. If you wait until it’s not working and pop it off then, you can just check for ice on your own. If you do that it’ll be important to note if the entire coil is evenly covered with ice or if there’s a lot on one part on none/very little on another part as these situations mean very different things.
One last thing, any AC, even a properly working one is really going to struggle to get a house down from 95+ to 75. You really should expect that to take several hours. If it’s humid out it’s going to take even longer.
Oh, and if there is ice, don’t succumb to the temptation to chip it off with a screwdriver or the like. It’s all too easy to puncture the evaporator coils and end up with a refrigerant leak and a much more expensive repair job.
Are you turning off your A/C during the day for some reason (like when you leave, etc.) and letting your house temp go up to 95 or so, and then turning on the A/C when you return?
If so, it probably would be better on the system to set your thermostat at 78/80 when you leave, and then turn it back down to your desired 75 when you get back. That way your unit isn’t working so hard to get it back down.
Go to your outside compressor and feel the copper pipes coming out of it. There will be two–a bigger one and a littler one. The big one should feel cold. Feel it both when it’s working well and not. If they feel just as cold both times, your coil may be icing over.
Do you have a lot of closed off vents? If so, open them. Closed vents will reduce your airflow and can contribute to the iced over coils.
Do you have a neighbor with a similar AC? Feel the pipes on his and compare it to yours. If
yours feels significantly warmer, you may be low on freon.
You can also check how clean the outside unit is. The cooling fins can get clogged by grass clippings, leaves, dandelion fuzz, etc. It can be hosed down easy enough.
Also, concerning the possible icing, there will obviously be condensation on the coils, that water need to go somewhere and there should be some kind of drainage, if you can, make sure it is not clogged.
Joey P–just curious: why does the humidity affect how long it takes for the system to cool the house?
MikeS–duly noted! I like to think I’ve grown out of solving problems by jabbing them with screwdrivers, but the extreme heat can certainly affect one’s state of mind…
Omar Little–it’s pretty rare that we’d be trying to cool it down from 90F or above (someone’s almost always home during the day), but it certainly makes sense to not have to make it do that much work if it can be avoided.
Filmore–all vents are open. As for the outside pipes, I’ll have to check that out (although I don’t recall any exposed copper–would it make sense that they’d be wrapped in some kind of foam insulation? Not at home at the moment…)
Hampshire–it’s fairly clean. That was one of the first things I thought to check after the filter, since both are within the realm of things Mllz can observe and quickly prolcaim “hmm… that ain’t right!”
Two reasons
1)As the evaporator (the part inside the house) cools down, humidity condenses on it. This is the water you see draining out the bottom. This takes energy…energy that would otherwise be used for cooling your house. If it weren’t humid out (and in your house as well) more of that cold freon would go towards cooling the warm air then removing humidity.
Various problems can cause that humidity to form ice on your evaporator coil. This’ll restrict airflow which means less cool air getting into the house.
Shutting off the AC, but leaving the (indoor) fan running will melt off the ice.
The first reason is the main reason why high humidity means it takes longer for your house to cool down. The second reason is often (but not always) a symptom of a bigger problem, but it’ll show up more often during times of high humidity.
Just spoke to a friend who is an HVAC guy. THE place to start is with the intake vent and the room outlets. With home A/C systems there should be a 20 degree air temperature differential between the two. He allows for very slight variation, but not much. If you don’t have this there is a problem somewhere, and not necessarilly a major one.
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I’ve also got an A/C problem that I’m asking about in a separate thread, so as not to hijack this one. Any help from any A/C experts in here will be greatly appreciated. Thanks!
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About that delta T - what if it’s low? Mine is 13 degrees, as measured with a probe thermometer at the main air return and a couple inches past the evaporator.
