It's much easier to maintain a comfortable temperature if your start air conditioning before temperatures rise to an uncomfortable level. Unlike the air conditioner in your car, a properly sized residential AC unit isn't designed to lower temperatures rapidly. It will perform much better if you set the thermostat for your desired comfort level and let the AC come on as needed to maintain that level.

Turning on the AC in an already overheated house will probably prevent temperatues from rising any more, but it will take a number of hours and possibly overnight to lower temperatures significantly.

Assuming that the AC comes on in the late morning on a hot day, it may cycle on and off initially, but if it's sized properly, during the hottest part of the afternoon it should run continuously while maintaining interior temperatures at your chosen level. Contrary to what many people think, an AC unit is most efficient when running continuously. An AC unit that cycles on and off during the hottest part of the day is probably oversized and wasting energy.

3 ton and 1200 sq feet? Am I thinking oversize? Without calculations done one may not be sure?

Start documenting indoor/outdoor temps as well as various room temps for future use as well as time a/c is turned on and how it cycles on and off if it does.

4th of July: If you are home, start the a/c at 8:00am after recording temps as mentioned and leave the tstat set at one temp, say 76-78. Does it reach that temp? When? Does the unit maintain that (or another temp you set) for the remainder of the day?

What filter are you using?

Thanks for all the responses. I will follow the advice. I have filters that are made of a mesh vinyl and are cleanable. Maybe I should find some other kind? I did notice that one side of the louvers of the outside unit is placed 2-4 inches from the wall--not the recommended minimum of 6 inches in the instructions. The unit is not cycling. It has been staying on all day, keeping an even 76 degrees in plus 100 weather here today. Keep in mind that I downsized from the original owner's 3.5 ton Gaffer Sattler's unit, but I might still be oversized, though it isn't cycling, and I am challenged in the insulation department. Perhaps it is even undersized?

You have to remember, the a/c is not just having to cool the air, but the walls, ceiling, furniture, and everything in the house. You should notice the air is cooler after 30 minutes, but the heat still remain.
Insulate your home- the cost will pay for itself the first year. However- the a/c may be over sized then. That's why I always try and get folks to insulate and tighten a home before or during installing a new system. If I size a system for that, then they have to do it and promise in writing, so they don't blame me if it runs all the time.
I did a liquor store that got up to 85 degrees before we got the a/c going- it took about 30+ hours to cool all that liquid back down.

We moved from a swamp cooler to real AC a few years ago. The first time we had our new system on it took hours to bring the temp down (hours as in all day and into the evening). After that it did OK (although it often ran constantly to maintain 75° in hotter weather). And once the outside temps reached the high 90s and higher it really struggled to get to a 75° set point, often only able to maintain 78° at best when set for 75°.

We always had insulation in the attic, but just that alone was not enough. Over time we've replaced our leaky 40+ year old single pane casement windows with modern double pane low-e units, did a LOT of work on the ducting and this year added some power attic venting. Now for the first time, after adding the attic venting the system *finally* works like I always thought it should, maintaining an even 75° in 100°+ weather without straining to do it. It still runs a lot in 100° weather, but not like it used to. Each improvement helped but it took all of them together to really get things working right.

I also agree with daddo, this kind of stuff should be done before the AC gets put in but we'd never had a refrigerated system before and just didn't know what it was ultimately going to take to get it right.

Some friends of ours put the same system in their house at the same time we had ours installed. Their house was only a few years old where ours is 40+ years old. All they had to do was get the outside compressor and coil put in and they were done and it all worked as it should. We had to get our electrical service upgraded, a new furnace installed PLUS all that other stuff above to get ours working. Point being every house is different and will require different things to get the AC to work the way it should.

Current AC systems don't bring the temps down quickly. Even the commercial system at my office building took all day and all night to return everything to normal after it had a problem and shut off over a weekend.

If your 'poorly insulated' house also leaks a lot of air, then you're cooling the outside too - It sounds like that may be your problem because a 3 ton unit should cool a 1200 sq ft house rather easily . . . . even if it's 100 degrees outside

I would add insulation where ever it's cost effective to do so (the attic for starters) and go on a 'seal it up' campaign, caulking all cracks and crevices, replacing the weatherstripping in all the doors and windows, adding thermopane windows (even the tape on, inside type) and see if that doesn't make a big difference in your cooling effectiveness . . . . and your energy bills

Don

My house is a 1938 cottage. Today it is 95 degrees and the new 3 ton A/C is running all the time to keep us at 78 degrees. There is some of that crumbly insulation in the attic and at one time I did put down some insulation in the parts of the attic I could reach but it had no effect then.

The A/C installer was out yesterday to change the secondary pipe. The water condensation was coming out of the secondary instead of the primary because they had mixed them up and it was dripping on the side of the outside unit. He checked the freon and told me he added a little extra to the amount that came with the manufacturer. Said it would make the air colder.

Also, when I went up to the attic to look at the inside unit, I noticed a gash in the metal tape on the unit abutting the new furnace. When I put my hand there, a lot of air was coming out of it. I found 2 other "leaks" and took off some of the extra metal tape and covered the holes. Could that be a problem?

Ultimately, I am wondering if the problem is a) the house is full of leaks and poorly insulated or b) the installers did not do their job or c) both of the above.

Thanks for the help...

Sorry to piggy back onto this message but was unable to figure out how to start a new question. I need to know the size in BTUs that I need to cool an apartment whose livingroom is 20'x13' and has a 10' ceiling. I rent the apartment and the tenant is complaining that cold air comes out of the present 8,000 BTU A/C but doesn't do much for the room temp.

Would replacing it with a 12,000 BTU wall unit do it or would that be a waste of money and energy?

"Also, when I went up to the attic to look at the inside unit, I noticed a gash in the metal tape on the unit abutting the new furnace. When I put my hand there, a lot of air was coming out of it. I found 2 other "leaks" and took off some of the extra metal tape and covered the holes. Could that be a problem?"

- Take the installer back into the attic with you and have him explain his lousy installation. Sounds like the attic is being cooled when it shouldn't.

"Ultimately, I am wondering if the problem is a) the house is full of leaks and poorly insulated or b) the installers did not do their job or c) both of the above."

- C. You need to correct both.

Best of luck to you.

I've got the installer coming out early next week. He only appeared in the morning and left installation to his underlings (he tells me all are on the payroll though!). He said the condenser or coil--I am not sure which--gives off some air. If anyone is interested in seeing a pic of the unit with the air leaks, I could send a pic that I took with the leaks circled in red. Now he also says something about the possibility of the ducts having leaks...

Rollie:

Post your pics as an attachment.

Sounds like he's laying the path for excuses for a sh*tty install. Stand your ground and get what you want and paid for.

I have no idea how to do an attachment here. Can anyone tell me how to do it?

Can someone tell me how o post a new question at this site? I don't mind if you email me directly. My screen name is chestman325-john2@yahoo.com...and I could really use someone help on what I hope is a simple solution

Just do what you are doing here except at the home page for heating and air conditioning. I believe the page asks you if you want to post at the bottom. Log in and post!

Here is a photo of the furnace with the leaks (circled in red) that I found.

Here is a link that might be useful: {{gwi:1582041}}

Whoops-wife posted the wrong photo for me...here's the one with the leaks circled. The other one previously posted shows an upper duct that is leaking air slightly where it connects with metal tape around it.

Here is a link that might be useful: {{gwi:1582043}}

3 tonne 1200 sqft...thats way oversized. You should be at a 1.5 tonne. 2 tonne max..depending on your sun exposure.

Now that it's been 13 years since the last post before the preceding one, it will soon be time to replace the unit that was the subject of this thread and a smaller one can be chosen if desired.

I just got a new UNIT installed how long do it take to cool off my house thermothermostat 70 and house is at 8