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new air conditioner works too well
Old 08-18-2013, 10:36 AM   #1
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new air conditioner works too well

The new air conditioner has been installed. The problem is, it works too well. When it goes on, the air comes out forcefully and it does go into all the rooms of the house (which is a good thing).

The problem is, the air coming out is too cold. I mean, really, really cold. So, after about two minutes of it being on, we need to turn it off, or put on warmer clothing. And, all this happens when the air conditioning is set for 79 degrees.

Now, we did get a power booster (or some such thing) along with the air conditioner unit. Could that be the problem or part of the problem?
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Old 08-18-2013, 10:57 AM   #2
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Have you checked the thermostat to be sure it's operating properly?
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Old 08-18-2013, 11:32 AM   #3
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Sounds like it may be too powerful (too many BTUs) for your home.
If so, it will run less often, and won't give you the dehumidifying benefit it should.

Did you or the installer double check the capacity before buying it?
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Old 08-18-2013, 01:07 PM   #4
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redduck,
In the previous thread on your AC system, a few people mentioned the high importance of actually performing a heat load computation. It's easy, you can do it yourself or have the contractor do it >and check their work<. So, how many BTUs did it turn out that your house requires? Does the BTU/tonnage of the installed AC unit match that?
It's hard to estimate the actual temperature of the air coming out of a register.
If the unit is oversized, it will do just what you are describing--come on for only a short bit and the air will be very cold. The house temp will quickly reach the set thermostat temperature and the unit will click off. Because only a small amount of air went over the coils, an insufficient amount of moisture will have been removed and your house will feel clammy and humid. It may even develop mold issues. Also, because the fan won't be running long, the temperature in the house will tend to fluctuate a bit more than if a smaller, properly-sized unit were installed.
A "booster fan" would result in more air reaching the rooms, but it would be slightly warmer air.
I think you need to check the calculations against the dataplate on the machine, and be prepared to call the contractor. You want a comfortable house, you paid for one. Specifically ask to see the heat load calculation they did, and confirm that the numbers are right. You'll need climatic data for your area and the rest of the stuff can be figured out with a tape measure. Let us know if you want to do this now, there are good online calculators that allow you to do a "Manual J" approximation.
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Old 08-18-2013, 01:32 PM   #5
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Did the contractor give you a good deal on an AC that will cool real good?
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Old 08-18-2013, 02:14 PM   #6
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I think we got the tonnage right. I'm a bit lost about the BTU thing, but the air conditioner guy is coming Tuesday to check out the system. I'm going to print samclem's post and let the contractor figure or re-figure this stuff out.

As an aside, the LENNOX thermostat is faulty, the digital numbers don't display correctly. So, 80 degrees looks like 90 degrees in the display window. I guess that's an easy one to take care of.
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Old 08-18-2013, 02:15 PM   #7
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Quote:
Originally Posted by ls99 View Post
Did the contractor give you a good deal on an AC that will cool real good?
Apparently not as good as I hoped for.
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Old 08-18-2013, 02:37 PM   #8
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We had the same problem in our manufactured home in Florida. In our case, the vents were improperly sized, allowing the living room to be too cold and the end of the house bedroom and sun room to be too warm. Since we had flexible duct, the A/C guy put in a simple deflector for the main room, and it equalized the rest of the house. I suspect our A/C Heat Pump was sized for the original design of the home before the sunroom was added.
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Old 08-18-2013, 02:49 PM   #9
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Quote:
Originally Posted by imoldernu View Post
We had the same problem in our manufactured home in Florida. In our case, the vents were improperly sized, allowing the living room to be too cold and the end of the house bedroom and sun room to be too warm. Since we had flexible duct, the A/C guy put in a simple deflector for the main room, and it equalized the rest of the house. I suspect our A/C Heat Pump was sized for the original design of the home before the sunroom was added.
Thank you.

I'll be printing out your response as well.

Maybe this deflector idea will take care of a few rooms at least, leaving one room where we can freeze meat on a hook.
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Old 08-18-2013, 03:46 PM   #10
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[QUOTE=samclem;1349964]redduck,
In the previous thread on your AC system, a few people mentioned the high importance of actually performing a heat load computation. It's easy, you can do it yourself or have the contractor do it >and check their work<. So, how many BTUs did it turn out that your house requires? Does the BTU/tonnage of the installed AC unit match that?

RE: the BTU: the best I could find was PSI of 450. I'll get the BTU figure on Tues.

The house is 2800 square feet (not counting the garage--which doesn't get the air conditioning). We got the 5 tonnage AC unit.
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Old 08-18-2013, 03:51 PM   #11
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If the guy goes out to his truck and comes back in 15 minutes saying "yep, it's the right size" don't be surprised. He listened to the radio and played solitaire on his phone. The folks I called to my house to install a furnace simply wouldn't do the thorough calculation, they wanted to use the data from the old furnace or their "rule of thumb" (based only on the square footage of the house) even though I asked them to do the calculation. Every company I called wanted to install equipment that was too big.

Here's a good online calculator that replicates the Manual J computations.
Space-Pak calculator.

Notes:
- For "Cooling Outdoor Temperature" use 95 degrees. The recommended cooling design temp for LA is 90 degrees, but from what I recall there are enough days warmer than that that 95 is probably a safer bet.
- For "Number of rooms" count significant hallways that have any external walls (walls that abut the outside" as a "room"
- For each room, disregard the "people" entry unless there will be a lot of people there at one time (a conference room, etc.
- If you don't have a system that deliberately ventilates the house with fresh air from outside (most homes don't have such a thing), then pick "Infiltration BTU/HR SQ FT Exposed wall" for "Makeup Air Conditions"
- "Exposed Walls" are the walls in a room that are exposed to the outside. Don't include walls that have a heated/cooled space on the other side.
- Doors and windows: Enter data only for those that are exposed to the outside (i.e. not a door that leads to a hallway or another room). ALso, it says "Window areas are optional", but you should be sure to enter them, and pick the type of window that is closest to the type you have. Window area should be entered in sq feet.
- You don't need to be exact on any of this stuff, you just want to know if your AC is way too big. So, make a guess if you aren't sure of a particular entry, it will probably be close enough.
- When they ask for "location of the unit" they mean the condenser coil for the AC unit. That's the part of the AC system that is inside your house (in California they usually put them in the attic or in a small utility room/closet).

If you (or your contractor) don't like the calculator above, you may prefer this one. It doesn't go room-by-room, but instead the data for each exterior wall of the home is entered on a single page.

Good luck.
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Old 08-18-2013, 03:53 PM   #12
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Is it possible that the a/c air seems extra cold because it's not all that warm/hot in the house when I turn on the a/c? So, the cold air isn't mingling with hot air and therefore doesn't warm up much when it hits the only mildly warm air in the house (let's say 80 degrees, as opposed to 90 degrees). Just wondering.
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Old 08-18-2013, 04:09 PM   #13
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Sorry, the condenser is outside. Evaporator coil is inside.
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Old 08-18-2013, 04:15 PM   #14
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Quote:
Originally Posted by redduck View Post
Is it possible that the a/c air seems extra cold because it's not all that warm/hot in the house when I turn on the a/c? So, the cold air isn't mingling with hot air and therefore doesn't warm up much when it hits the only mildly warm air in the house (let's say 80 degrees, as opposed to 90 degrees). Just wondering.
Or could it be that redduck is not accustomed to being this cool, meaning he has been a warmduck all these years, and has yet to learn to be a coldduck?

Hmm... Talk about coldduck reminds me of "cold duck champagne". Off to the Web I go, to do some research on what the latter is all about.

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Sorry, the condenser is outside. Evaporator coil is inside.
... until you switch it into heat pump mode, and the flow is reversed.
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Old 08-18-2013, 04:24 PM   #15
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This afternoon it is supposed to get to be about 90-95 deg F near you. That's probably close to the limit that your system was designed to handle. If that's right, and if you've got your thermostat at a normal setting (72-75 deg--if you want to do this test, then put it there even if you normally keep your home warmer) then your AC unit should be on a lot if it is the right size. I don't have an exact % for you, but if it's only running for 1/4th of the time, for example, then it is definitely too big.

Regarding the temp of the air coming out of the registers: Most systems are designed so that the air coming out of the registers is about 15-20 degrees cooler than the air that enters the AC system through the "return air" grill. This has to be measured after the system has been running awhile (15 minutes or so). You'll need a real thermometer to check this.

I'm sure a true AC pro will be along shortly to give more precise info!
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Old 08-18-2013, 04:25 PM   #16
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Originally Posted by HFWR View Post
Sorry, the condenser is outside. Evaporator coil is inside.
Right-o. Thanks.
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Old 08-19-2013, 03:53 AM   #17
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Originally Posted by redduck View Post
The house is 2800 square feet (not counting the garage--which doesn't get the air conditioning). We got the 5 tonnage AC unit.
Okay, if you bought a 5 ton unit, we know the approx BTUs of cooling it provides: A "ton" equals 12,000 BTU. So your new unit provides approximately 60,000 BTU.

Here's the important question: What was the size (tons) of your old unit, and how well did it perform when it was running well?
- Did it keep your home cool enough on the hottest days?
- When it was hot and humid outside (not a common occurrence in Los Angeles!) did it feel humid inside your home?
- When your old AC was in good shape, did it seem to be running a lot (i.e. most of the time) on your very hottest days?

If you don't know the tonnage of your old unit, we can probably find it if you know the serial number and the brand of the unit.
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Old 08-19-2013, 09:16 AM   #18
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Either the outlet vents are aimed directly at you (instant chill), an outlet vent is too close to the inlet (cooling pre-cooled air), the thermostat is too far away from any of the outlet vents (AC stays on/off longer than necessary), or the AC is too large for your needs. 5 tons is pretty big if you're just looking for a 10-20 degree cool down, depending on the size and insulation of your house of course. If the AC only needs to turn on in two minute spurts when it's really hot out, it's too large. It ought to be staying on over 50% of the time when it's really working. Lots of stops and starts are inefficient, and give you short bursts of really cold air instead of longer bursts of cool air.

If you can direct the air from the outlet vents towards the ceiling so they don't blow directly at you, that will help mix the air before it gets to you.

Check to see what the temperature min and max is in the places you care about. It shouldn't vary more than a couple of degrees. A thermostat adjustment, vent adjustment, or thermostat relocation might be required to minimize a large temp swing.
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Old 08-19-2013, 09:53 AM   #19
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Originally Posted by samclem View Post
Okay, if you bought a 5 ton unit, we know the approx BTUs of cooling it provides: A "ton" equals 12,000 BTU. So your new unit provides approximately 60,000 BTU.

Here's the important question: What was the size (tons) of your old unit, and how well did it perform when it was running well?
- Did it keep your home cool enough on the hottest days?
- When it was hot and humid outside (not a common occurrence in Los Angeles!) did it feel humid inside your home?
- When your old AC was in good shape, did it seem to be running a lot (i.e. most of the time) on your very hottest days?

If you don't know the tonnage of your old unit, we can probably find it if you know the serial number and the brand of the unit.
1. Sorry, I don't remember the brand name and we don't have the serial number.

2. The unit we replaced came with the house. The house was built around 1962.

3. The air conditioning/heating barely got into the living room and the back rooms of the house. So, no, it did not do a very good job of cooling off the house on the hottest days. And, I don't recall the unit ever running all that well, but it was running less well the last few years.

4. Humidity is not much of a problem here, so it's hard to ascertain what effect/affect(?) the unit had on humidity.

5. We had two HVAC people come out here before we went ahead with the project. Both said we needed a 5 ton unit.

6. If you are seeking to know the temperature where I live, you either need to add 5 degrees to the Los Angeles weather or subtract 5 degree from the temperature in Studio City, CA. That gets you close to our temperature.

7. When I retire, I hope that you will give me this much guidance in financial matters.
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Old 08-19-2013, 10:03 AM   #20
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Originally Posted by Animorph View Post
Either the outlet vents are aimed directly at you (instant chill), an outlet vent is too close to the inlet (cooling pre-cooled air), the thermostat is too far away from any of the outlet vents (AC stays on/off longer than necessary), or the AC is too large for your needs. 5 tons is pretty big if you're just looking for a 10-20 degree cool down, depending on the size and insulation of your house of course. If the AC only needs to turn on in two minute spurts when it's really hot out, it's too large. It ought to be staying on over 50% of the time when it's really working. Lots of stops and starts are inefficient, and give you short bursts of really cold air instead of longer bursts of cool air.

If you can direct the air from the outlet vents towards the ceiling so they don't blow directly at you, that will help mix the air before it gets to you.

Check to see what the temperature min and max is in the places you care about. It shouldn't vary more than a couple of degrees. A thermostat adjustment, vent adjustment, or thermostat relocation might be required to minimize a large temp swing.
Let me try to respond to your helpful post:

1. The vents are where they have always been and they are not aiming directly at anyone.

2. The thermostat is fairly close to one vent.

3. It has not yet been really hot here, but the A/C does not do that short burst thing--it stays on for way longer than I want it to. We are getting very cold air for too long a period.

4. The vent shutters are pointed towards the ceiling.

5. I'm calling the HVAC guy this morning, to prepare him for his scheduled visit tomorrow.

6. Thanks.
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