Check my logic here (HVAC)

[Gordon Shumway]

Originally Posted by aerovette

As my original post says, I suspect the warmest rooms are warmest BECAUSE that's where the returns are.

Air exiting the ducts is measuring about 65 - 67 degrees.

The split between your return air (75) and cooled air (65-67) is way too low. It should be around 20 degrees, and that's the A/C.

Of course, the 98-100 degree outside air isn't helping the issue. At those temps I wouldn't try to run it any lower than about 78.

[DAB]

oh yeah, limit the amount of fresh air you are drawing in.

i'd open all the registers upstairs, and close off/limit the return vents upstairs.

put cool air where it is warm, the cool air will eventually sink downstairs, and i'd open all the return vents downstairs.

blue tape and some paper will suffice for short term to close off return vents.

[Bill]

Originally Posted by Rodnok1

Don't forget sun load from windows, not only quality of windows but just the heat. We always close blinds on sunny side during summer and it helps immensely. I need to get heavier curtains actually.

I put 70% solar screens on every window that gets any afternoon sun, and keep all the wood blinds closed, and have a piece of insulated house wrap in my largest western facing window, a guest bedroom. I probably need heavy drapes too, on those western facing windows, too.

[slewfoot]

What is the outside temperature in the afternoon?

[slewfoot]

Originally Posted by bill_daniels

I put 70% solar screens on every window that gets any afternoon sun, and keep all the wood blinds closed, and have a piece of insulated house wrap in my largest western facing window, a guest bedroom. I probably need heavy drapes too, on those western facing windows, too.

On the west side of ours, I have the old fashion roll ups as a shade and white wooden blinds. Works pretty good. Main problem is our master bedroom is over the garage.

To help I cut out a spot in the ceiling and put in a register to draft the hot air into the attic area and out the roof vents

[Aerovette]

Originally Posted by slewfoot

What is the outside temperature in the afternoon?

98 today.

[Aerovette]

I have ridge vents, I have soffit vents, I have techshield, I have about 14 inches of insulation. It was 18 but it is settling. I have two units. One for upstairs and one for downstairs.

I have friends that keep their AC on 68 all summer so I know something isn't right.

[Aerovette]

Originally Posted by DAB

oh yeah, limit the amount of fresh air you are drawing in.

i'd open all the registers upstairs, and close off/limit the return vents upstairs.

put cool air where it is warm, the cool air will eventually sink downstairs, and i'd open all the return vents downstairs.

blue tape and some paper will suffice for short term to close off return vents.

There is one central return vent for the entire upstairs and one for downstairs.

Both are 30x 25

[benny42]

The key is your 10* delta. The 65* supply air and 75* return says that unit is not doing what it is capable of. It may have a dirty condenser, low charge, aftermarket fan motor or blade (of the wrong size), etc. Have you checked the charge lately, or had it done? I'm surprised its achieving 75* like it is.

[Stangkiller]

Originally Posted by aerovette

As my original post says, I suspect the warmest rooms are warmest BECAUSE that's where the returns are.

Air exiting the ducts is measuring about 65 - 67 degrees.

This is what I was going to ask, what's the temp at the return vs the temp coming out of the AC, if you have 12+ degrees separation it's not your AC's fault, but the house just isn't built for these 100* days.

For reference I keep the house at 77* during the day and 73* at night after that bs freeze last year I removed the blown in insulation and replaced with spray foam. Yesterday my two units in the house ran for a combined 17 hours (newer 5ton and 3ton units).

My Apartment AC (old 2 ton R22 unit) only ran for 3.5hrs yesterday to keep the apartment at a constant 85* (also has spray foam in the attic)

[Bill]

Originally Posted by DAB

oh yeah, limit the amount of fresh air you are drawing in.

i'd open all the registers upstairs, and close off/limit the return vents upstairs.

put cool air where it is warm, the cool air will eventually sink downstairs, and i'd open all the return vents downstairs.

blue tape and some paper will suffice for short term to close off return vents.

I guess I don't understand this. I, like Jeff, have two units, upstairs and down. Each unit has one return air duct, which is where the filters are installed. If I block off the where the upstairs system sucks in air, am I not basically making it difficult for the system to breathe? That seems like a guaranteed way to make the unit fail quickly.

[ToolMaker]

I have a passive solar house.
The glass only shaded on the inside cuts down about half of the gain compared to shading from the outside, in my situation.
You are still letting the window coverings inside to get hot.
This as well as the other suggestions should help.

[Stangkiller]

Originally Posted by bill_daniels

I guess I don't understand this. I, like Jeff, have two units, upstairs and down. Each unit has one return air duct, which is where the filters are installed. If I block off the where the upstairs system sucks in air, am I not basically making it difficult for the system to breathe? That seems like a guaranteed way to make the unit fail quickly.

Yup it'll freeze up pretty quickly. Maybe Dabs suggesting to close off and not cool the rooms upstairs that you don't need to cool? Closing those doors will help create back pressure and push cold air to the open spaces too.

[Mick]

Originally Posted by bill_daniels

The simple answer is, you're pushing the limits of what your A/C can do. Yes, the more well insulated your house is, the better, and shade trees are definitely a help, especially if they block the sun on your roof on the west side of the house. Having said all that, your A/C is only going to cool the air so much. If you're running it so that it virtually never shuts off, you're just riding that Pony Express horse to exhaustion, and sooner or later you are going to kill your A/C. I'd suggest just adjusting yourself to the season, keep it set at 80-82 during the day when you aren't home, and bump that A/C to 78, maybe 79, when you arrive home, and use ceiling fans. Maybe bump the temperature down a bit at night, after the Sun has gone down if that helps you sleep at night.

When it's 100 outside and you're trying to force 75 inside the house, unless your house is super insulated, of course that A/C is going to struggle.

The best bang for the buck, I think, is improving attic insulation, adding a radiant barrier, maybe even solar roof fans, but of course, all this isn't really practical to do right now. You have to do that when it's cool outside.

One thing you can do now is clean your A/C coils. Do it early in the morning. Shut them off, spray coil cleaner on the coils, let is sit, then use your garden hose to clean them off. If you haven't done that in a while that will help the units function better, as they can throw off more heat with clean fins.

This is more or less wrong. AC systems don't "get tired" from running continuously. I suppose they have a lifespan that has a limited number of hours of operation before the unit is just plain worn out. If you are worried about that, the best thing to do is not run AC at all except on the very hottest of days. If you do this, you may succeed in extending the life of the unit until corrosion or something else kills it. This is not something I worry about.

At my house, I only cool to 76-78, and don't turn the AC on unless the temp reaches the high 80s or more, mostly because I prefer fresh air. On 100 degree days, the AC rarely comes on in the morning because trees block the East side of the house, and in the afternoon, when the sun is beating on the house unimpeded, the system will run continuously to maintain 78, sometimes going up to 79. This is because the house is taking in the maximum amount of heat, or slightly more than the maximum, than the system can remove. My alternatives are laid out well in other posts: better insulation, bigger unit, etc., but it really doesn't bother me, so I have done nothing about it.

[Aerovette]

In reading all of the posted replies and considering both AC units are 15 years old, I guess they are doing what they are supposed to, as well as they can. I can get the downstairs temperature to about 71 if I choose to. Upstairs that will never happen. The delta donwnstairs is 10* but it's set at 72 right now. Upstairs is 9* and it is set on 74.

Outside coils are clean. I have not looked at the inside since last year.

[Stangkiller]

Originally Posted by aerovette

In reading all of the posted replies and considering both AC units are 15 years old, I guess they are doing what they are supposed to, as well as they can. I can get the downstairs temperature to about 71 if I choose to. Upstairs that will never happen. The delta donwnstairs is 10* but it's set at 72 right now. Upstairs is 9* and it is set on 74.

Outside coils are clean. I have not looked at the inside since last year.

Do you have a big open space between the floors like my last house? Do you have a big fan mixing the air in the open spaces?

[Aerovette]

Originally Posted by Stangkiller

Do you have a big open space between the floors like my last house? Do you have a big fan mixing the air in the open spaces?

Yes and yes

[Aerovette]

I'm still stuck on something. If the AC can get the house to the set temperature, but it runs 17 hours with short "off" cycles, it seems to me it is an insulation issue. It is not able to cool and RETAIN the cool air. Hot is leaking in/cold leaking out.

Low refrigerant would prevent me from getting to the set temperature ( I've had this issue before)

Fair statement?

[DAB]

check your coils for dirt.

[ThePirate]

Originally Posted by aerovette

'Splain me please.

If the AC is one speed and set to a certain temperature, it cycles on and off very frequently. This doesn't allow the AC to properly dehumidify your house and it seems hotter than it is set to.