HVAC system 20 degree rule

Try telling that to the people in Phoenix when it hit 118 a couple weeks ago.

Load of bunk. If this were true the food in your freezer would be thawing....

Something's got to be wrong if your old 3-ton unit was adequate.

I'd have a blower door and load analysis done on the house to see how the numbers come up. You might also get a thermometer and read the temperatures going into and coming out of the AC at the closest register (after it's been running constantly for maybe 1/2 hour) to see if the differential is in the right ballpark. Did they tell you the capacity of the air handler in cubic feet/minute? You can have someone do calculations given the humidity, temperature differential and air handler cfm's to see if you're roughly getting what you should out of the system.

In Arizona it can be 120 degrees outside and plenty of houses and buildings are 70 degrees or so inside!

Might want to have another company look at your system. Maybe they did not install what you paid for? Something is fishy here.

If you can, post the brand and model of your 4 ton unit (read label on unit) here along with the square footage of your house. One or more of the experts here should be able to tell you if this is in fact a 4 ton unit.

The 20 degree rule applies to the difference between the air at the return and what's coming out of the registers. I'd _guess_ there is either something wrong or you have a very poorly insulated/leaky house.

I'm no A/C expert but even I know that four tons for 2500 sq. ft. is too little. I've come to believe that the rule of thumb (for standard eight foot ceilings) is one ton for every 400 sq. ft. I think you're a couple of tons short.

In south Florida the rule of thumb is 600 sq ft per ton. If the A/C is oversized then it doesn't run long enough to remove the humidity.

and what's coming out of the registers. I'd _guess_

house. 4 tons for the avg 2500 sq ft house should be

little. I've come to believe that the rule of thumb

you're a couple of tons short.

It was 102F outside the other day (not counting the fact there was also high humidity, which apparently made it feel like 117, and the A/C happily kept the house at 72F. I have a 2 tonne air conditioner, total condition space is 2000 sq ft with 8ft ceilings well sealed.

PS. I also have a heat recovery ventilator and didn't need to switch it to recirc or having to run any additional dehumidifier, the A/C removed any extra humidity the HRV might have been bringing in.

David

OK, Sorry for the delay in responding. I really appreciate all the list suggestions. It is a Copeland Scroll version of a unit made by Goodman Manufacturing company out of Houston, tx. the model number is #CLJ481-C. I hope this helps. IN the meantime I am having the a/c guys come back out to do the temp. comparisons. The unit is running almost constantly to attempt to reach a cooler temp, and there is a significantly higher temp near the ceilings. Thanks again!! Beth

I had a similar problem after a new install. Installer came back three times. Finally found freon leak under the insulation.

I had the exact same situation as Bill. A new installation of an A/C unit, the air that was coming out of the registers was not very cold, and it seemed that no matter how long we ran it, the house would not cool down much.

As time went on (for a couple of weeks) it got worse and worse until the A/C did no good at all. We called the contractor who found a leak in the freon. He fixed the leak, and the problem was instantly solved. Night and day difference, we had no problem (even on very hot days -

Searching on the internet I found that this is in fact a 4 ton unit...

Page 14 or search the text for CLJ481

"Bill" wrote in news:%C%Bg.6798$ snipped-for-privacy@bignews1.bellsouth.net:

I have an even better one. My ex moved into a trailer when she moved out last summer, one without A/C. She had a new furnace & A/C installed last Nov. This spring she finds out that the A/C apparently doesn't work.(NO cooling at ALL!) After several calls to the installer, she finally gets a response that turns out to be a different outfit responding to the call as a favor to the original co. since they are going belly up. After about 45 min. of trying to get some freon into the system since it is showing all the symptoms of being low, one of the guys decides to check something really stupid. It seems that compressors come pre-charged, and there is some sort of valve at the intake and output that needs to be opened when the system is being charged during install. You guessed it - they had not been opened yet. As soon as he started to open the valves heat started coming off of the heat exchanger and she was in business. Guess that's why the original outfit was going under!

Good point! You would assume that someone installing something would test it after installation to be sure everything is working properly, etc. However I have worked for many companies which have "that one new employee" who never does anything right, will not be sure everything is working before leaving, etc. So if you get a bad "luck of the draw", might get one of these guys installing something for you.

Usually the repair guys are well trained - experienced and can resolve these problems. The installation department has the new employees typically. (Sometimes a boss will keep sending the same installer out in an attempt to educate him so he will do things right in the future... "You will keep going out there until you get it working" is the thinking.)

replying to New Wave Dave, Imnukingfutz wrote: It may be fine and not undersized at all...I have 2300 sq ft and am only running a 3 ton system and it works perfectly. Many other factors come into play other than sq footage when sizing a system.