Expected A/C Splits/performance in 110F?

[ps2cho]

I had my house heat pumps replaced last year -- 3 ton Trane's. The other day ambient outside was 114F and the inside was set to 80F. Wanted it down to 76 and after 3hours it had only cooled from 80F to 79F. Air was going constantly. Is this ambient just too high to expect that ability, or could the installers have undercharged the unit?

Any suggestions? I installed a mini split myself last year as well so not completely inept, but anyone have any directions I should look at first? I dont have a hvac line temperature tool so to check it I know I'd need one (but before investing in one checking here first) - but do have a set of gauges for r410a from the mini split install.

 

[danski0224]

Was a load calculation performed?

What is summer design temperature in your area?

34 degree spread seems pretty good otherwise.

 

[BrandonV]

Probably need to have them show you the load calculation.

Design temperature for a place like Phoenix (as an example) is often 108F outside for a target 74F inside temperature. This week it's been 117F at the hottest part of the day.

 

[danski0224]

And just because one may have a load calculation, it doesn't mean that the ductwork can deliver it.

 

[ps2cho]

Was a load calculation performed?

What is summer design temperature in your area?

34 degree spread seems pretty good otherwise.

No J load -- the original units were 3 tons, so the company I used said they would have done a J load calc at build so they replaced with the same tonnage. Summer temps are 110-115F average.

I am just checking nothing is "wrong" -- I wouldnt say this houses insulation is anything but basic builder grade. So asking it to push the house down to 75F when its 115F outside might be asking a lot?

 

[fitter30]

Were the old units 3 ton ? If design temperature manual j 107° / 75° indoor. Temp gets to 114° add 7° to the 75°. A energy audit with a blower door test would be helpful check with your electric company.

 

[ps2cho]

Were the old units 3 ton ? If design temperature manual j 107° / 75° indoor. Temp gets to 114° add 7° to the 75°. A energy audit with a blower door test would be helpful check with your electric company.

Yes correct - 3 ton units when the house was built in 2002. Like for like replacement.

 

[danski0224]

Yes correct - 3 ton units when the house was built in 2002. Like for like replacement.

Doesn't mean that it was correct to start, and possible (likely) ductwork issues.

 

[karoc]

Is this new problem or existing problem from day you moved in? Regardless where you’re at here in states ac systems are design for ambient temp of 97 in residential systems. If all is well mechanically the best is 30 degrees (I think)difference outside temp inside. Things to check is
1) grill temp and return air temp which if working should be 18 degrees if working correctly
2) Check to see if you have open return air, or pulling air from attic space. Maybe return air duct came off.
What I did in my younger days, but memory is slipping

 

[fitter30]

Doesn't mean that it was correct to start, and possible (likely) ductwork issues.

With a pocket or lead thermometer can take a temp at filter and 18"-2' from ac coil. difference 18-22° is exceptable.

 

[danski0224]

Airflow, not just temperature drop.

 

[theoldwizard1]

A couple of quick tips

• Shade the compressor.
• If the price of water is not ridiculous, mist the unit. They even make drip units that clip on to the outside.

 

[danski0224]

If the price of water is not ridiculous, mist the unit. They even make drip units that clip on to the outside.

If water quality is poor, there will be a bunch of mineral deposits to clean.

 

[Al G]

Regardless where you’re at here in states ac systems are design for ambient temp of 97 in residential systems. If all is well mechanically the best is 30 degrees (I think)difference outside temp inside.

I can't believe that's the case for residential systems in the SW desert. Summer temperatures here are routinely above 110 degrees and my system has no problem maintaining 75 in the house ( and even lower those few times I've asked it to).

 

[shade]

So much stupidity being thrown around.
Same as ^
I live in AZ and routinely in the 110s.
If AC systems couldnt reduce temps by more than 30 degrees there would be riots.
House can maintain 73* when it's 120 out. I have a normal units like many others.

 

[ericm]

The company I used said they would have done a J load calc at build

Yea sure.

But if your previous 3 ton system could cool to 76 at the same ambient temp, the new one ought to be able to do it too. If 110 is a new high for your area, then maybe you are exceeding the capacity of the system. If that's the case the suggestion to get a blower door test (and an efficiency eval with it) would be a good idea. Then you can fix the things the eval finds that will have the most payback. We did this and it made a noticeable difference.

 

[BrandonV]

I can't believe that's the case for residential systems in the SW desert. Summer temperatures here are routinely above 110 degrees and my system has no problem maintaining 75 in the house ( and even lower those few times I've asked it to).

Absolutely. They're not using 79 as a design temperature. The 1% ASHRAE temperature sits at 108.5. IPC has it at 107 with the indoor at 75.

So much stupidity being thrown around.
Same as ^
I live in AZ and routinely in the 110s.
If AC systems couldnt reduce temps by more than 30 degrees there would be riots.
House can maintain 73* when it's 120 out. I have a normal units like many others.

Installers tend to oversize. Manual J calculations also don't account for realistic thermal mass which is huge.

It usually boils down to insulation and windows. If you have bad insulation and old/crappy windows the unit will struggle. Home built in 1994, 5 ton HVAC, 2300 sq ft. unit during these hot streaks rarely if ever kicks into stage 2. I have the setpoint at 78. One room with four original windows and crappy insulation by the builder sits at 86F right now. Rest of the house is comfortable 78. If you have a new house they seem to size larger units than the manual J calculation calls for and people can set the thermostat all the way down to 72.

 

[karoc]

So much stupidity being thrown around.
Same as ^
I live in AZ and routinely in the 110s.
If AC systems couldnt reduce temps by more than 30 degrees there would be riots.
House can maintain 73* when it's 120 out. I have a normal units like many others.

I can’t imagine 110 outside temps, dang that’s hot. But it’s stupidity

 

[BrandonV]

I can’t imagine 110 outside temps, dang that’s hot. But it’s stupidity

Well that is why man invented HVAC .

 

[462867aa]

So many things could be wrong. Kinked ducts, under charge on refrigerant, under size, general poor installation. I had them all. Good luck!

 

[theoldwizard1]

I live in AZ and routinely in the 110s.
If AC systems couldnt reduce temps by more than 30 degrees there would be riots.

A lot depends on how well insulated the building is !

 

[karoc]

I was wrong about 30 difference outside and inside. 30 degrees is difference between air temp entering condenser coil and discharge air coming out condenser. In years that I ran roads doing service calls lot of problems like OP is having it was open return pulling attic air or unconditional air from some place through system.
Remembering one year durning hurricane season(right now) we loss power for week, no AC which it was in upper ninety’s here miserable. I can’t imagine having deal with 110 on up

 

[dcg9381]

A lot depends on how well insulated the building is !

This. If it's 110 outside, better hope your building is designed for it... If it's not designed for it, I'm starting with better insulation up above.

There is no real magic here, AC should decrease what? 30 degrees below "ambient" (inlet temp) so it's a function of air flow and how well insulated your building is. Typical construction in my region runs duct work through the super-heated attic, which is just dumb....

Traditional AC you'll need to run all the time in those types of conditions, they can't "overcapacity" traditional AC like you can with mini-splits that can throttle.. At least to some degree.

I have a shop that is "under-insulated" (budget) and over AC, which works well with mini-splits. It's use case is not full time AC. So if we do reach a good temperature, we just shut down one mini-split.

 

[P0234]

I'm not an HVAC tech, though I do own a siiick set of guages. As mentioned above, if the air coming out of your registers is 17-21 degrees cooler than the air going into the returns, your unit is working well enough to not suspect something wrong with its operation. Sizing is a different issue. Additionally the amount of shade around a house, how many windows, blinds/shades used, appliances used, etc, etc play an important part of the equation.

There are some good HVAC techs but a large number of them aren't the best. I had some sizing arguments with one at the last house I built. I knew the unit they wanted to put in was going to be too small. Its a vacation house, everyone comes in and showers at roughly the same time, people start cooking, dryer is running...etc...etc. Finally the guy had me sign some paperwork saying he wasn't responsible for mold or other issues by putting in a way oversized unit in the place. No mold issues. And the unit runs at 100% duty cycle at times with temps even creeping up at times. Sure glad I didn't listen to him.

 

[PoorUB]

So asking it to push the house down to 75F when its 115F outside might be asking a lot?

If the old units did the job, so should the new units.

That said, if they were sized properly, expecting them to pull the inside temps down at 117 outdoor temp may be too much to ask for assuming everything else if in good shape. They are working or the house temp would be going up.

Do you have a decent temp drop across the indoor coil? check return temp at the unit and supply temp, it should be around 20F if the AC has been on after a few hours. If the temp drop is something like 10F there is a problem.

Many installers don't do squat on start up. Flip the switch, it runs and blows cold air, good to go, lets grab a beer.

Fan speed could be set wrong, maybe they never checked subcooling and super heat, who knows. It is tough to find a good HVAC guy today!

My sister leaves her windows open and when it gets too hot she closes up the house and turns on a AC then complains that it takes so long to cool the house. I explained to her that filling the house full of 75-80 degree humid air and then expecting the AC to cool down fast is a hard battle to win. I tried to explain that early morning before it gets hot to close up the house and turn on the AC and she might have a chance. It isn't like you can't look at the weather forecast and decide early in the day! Better yet, in the heat of the summer, set the AC temp to where you want, leave it on and never open the windows.

 

[BrandonV]

If the old units did the job, so should the new units.

Most important thing. A 3 ton is a 3 ton. As long as the ductwork isn't damaged during install if it isn't working as well as the old system there is a problem an HVAC technician needs to investigate.

I've seen so many problems with new installs it's a given these days.

 

[u3b3rg33k]

I had my house heat pumps replaced last year -- 3 ton Trane's. The other day ambient outside was 114F and the inside was set to 80F. Wanted it down to 76 and after 3hours it had only cooled from 80F to 79F. Air was going constantly. Is this ambient just too high to expect that ability, or could the installers have undercharged the unit?

Any suggestions? I installed a mini split myself last year as well so not completely inept, but anyone have any directions I should look at first? I dont have a hvac line temperature tool so to check it I know I'd need one (but before investing in one checking here first) - but do have a set of gauges for r410a from the mini split install.

so this tells me that you're likely beyond the "design day" your area is built for, and you ARE getting temperature drop, which means your unit is PROBABLY working fine (unless it wasn't before on a similar day).

my place can only hold setpoint at 95F+. so if I have it set to 77 and want 75 and it's 100F outside? not gonna happen until evening.

TLDR: design day is the weather conditions that yield 100% runtime on your unit.

Setting the thermostat lower won't get you more cooling with a single stage, so best to set your thermostat where you want it to be on really hot days and don't expect it to pull down temps.

things to check:
outdoor coil clean? if it's dirty, that'll make it work harder and provide less cooling
indoor filter plugged? not enough airflow = less cooling delivered.
ALL your registers open 100%? you need airflow to make cooling happen
returns blocked by furniture/dustbunnies? same problem
close some shades/add some attic insulation?


the hotter it is outside vs inside, the more the little things matter.

re: your units, what model units do you have? outside AND inside. what thermostat as well.

A couple of quick tips

• Shade the compressor.
• If the price of water is not ridiculous, mist the unit. They even make drip units that clip on to the outside.

if you shade it be sure not to cause recirculation of hot air. that'll be worse for performance than the sun exposure.

mist AWAY from the unit if you can. cooling the ambient air around it lets the water evaporate and cool the air the condenser ***** up and will reduce mineral buildup/corrosion of the unit.

So much stupidity being thrown around.
Same as ^
I live in AZ and routinely in the 110s.
If AC systems couldnt reduce temps by more than 30 degrees there would be riots.
House can maintain 73* when it's 120 out. I have a normal units like many others.

YOUR house can. that's the part people forget. even with cookie cutter installs, the envelope matters bigtime!

 

[Jim greengo]

Don't leave it set at 80,then expect miracles.
Get it cooled down at night when there's not so much load on it,then try and maintain it during the day.
How does your insulation look in attic,are you keeping curtains closed to keep the sun out?

 

[rixtrix1]

Today it was 119. 1 year old 3t Trane unit had NO problem keeping our home at 78*. 41 year old, 1500 sq ft tract home with R40 attic insulation and good windows replaced 2 years ago. Could not tell it was any warmer than any other day. 24k mini split installed in my shop 2 weeks ago held 80* measured at 5' above the floor with the evap installed at 9' and set to 75*, R15 in all 4-10' walls and only a quarter of the ceiling done with R30. Inverter unit cycled up and down every so often. Condenser unit is shaded after 11.30am; home unit is on the roof.

DON'T use super great filters for your HVAC! You need good airflow. Use cheapie fiberglas ones and change them EVERY month. The HVAC UNIT is not there to clean your air(they make really good air cleaners for that. We use 2 Honeywell 3-piece hepa filter units for that.)

Seems you may have more of a problem with air leaking from ducts, windows, insulation and/or airflow.

 

[bonneyman]

Probably need to have them show you the load calculation.

Design temperature for a place like Phoenix (as an example) is often 108F outside for a target 74F inside temperature. This week it's been 117F at the hottest part of the day.

We had 111F this week in Tucson - and I thought that was bad! 117F?

And just because one may have a load calculation, it doesn't mean that the ductwork can deliver it.

Big 10-4. Ductwork is often poorly designed - and compromised - in my locale. I've been in attics where the flex duct system looked like someone's intestines! "Why is there poor airflow"?

 

[pcmeiners]

"Big 10-4. Ductwork is often poorly designed - and compromised - in my locale. I've been in attics where the flex duct system looked like someone's intestines!"

Then there is the fact flex duct is perfect for introducing friction loss due to the turbulence from the design. If you want friction it is a great design.

 

[BrandonV]

Just stumbled upon the ROC minimum standards today in Arizona.

Interesting. Guess they can get away with 78F here...

 

[CoronadoBruin]

I'd spend $100-$150 and have a reputable A/C service company come out and check everything (ducts, charge, etc.). Service companies are obscenely expensive so hire them for the trouble-shooting, but use someone else for the repair, if any.

We hit 123°F (50.5°C) six days ago in Palm Desert and it was an all-time high of 124° in Palm Springs the same day, then followed by a week of 119° and 120° days (it was crazy seeing a three-day forecast of all 121°). My top of the line 3T Lennox (installed by the previous owner and hugely expensive) isn't even breaking a sweat, and I keep it at 82°. Any colder like my many elderly neighbors and it is actually uncomfortable.

Another vote for the remark that ductwork is often compromised. It has been stepped on and crushed or it has separated, usually at the boot. I just had the evaporative coils replaced ($3,800) and the company insisted on checking the attic for that very issue of ductwork problems.

Full disclosure: I spent 45 years building residential housing and I don't know sh!t about HVAC. By far my weakest subject.

Positively chilly right now at 114° to 117°.

 

[ps2cho]

Right now - 8:30pm....ambient temp outside is 103F. New air filters installed. A/C has been running for 2+hrs. IR Thermometer at the return vent at the filter shows 80F. Vents around the house for output are showing 68F. So that is a 12 degree split.

Seems low...Would you guys recommend I get some thermocouplers and hook my gauge set up and get a subcooling value?

To confirm - I had new 2023 Trane XR16 heat pump and accompanying handler/blower. Paperwork on install shows 20F splits a year ago, wonder if there’s a leak maybe…but now’s the worst time to call them out, so maybe I can start by determine where the issue might be if any?

 

[u3b3rg33k]

what's the discharge plenum temp?

 

[ps2cho]

what's the discharge plenum temp?

Will check - but now I think on it logically, I have two units, and both upstairs and downstairs are outputting the same 12F split, which makes me wonder if they were just both undercharged. I’ll verify plenum temps tomorrow.
Units going almost 6hrs now and only cooled from 80 to 76…can’t be right.

 

[BrandonV]

Will check - but now I think on it logically, I have two units, and both upstairs and downstairs are outputting the same 12F split, which makes me wonder if they were just both undercharged. I’ll verify plenum temps tomorrow.
Units going almost 6hrs now and only cooled from 80 to 76…can’t be right.

Definitely a problem. I'm not sure where you are located but that sounds wrong in even the hottest of climates.

 

[ps2cho]

Definitely a problem. I'm not sure where you are located but that sounds wrong in even the hottest of climates.

I just went back through my phone camera and found a photo I took August 2023 so it was in the summer as well -- Splits were 20F, I measured 60F out of the same vent I checked the other day getting 68F, so there is a clear degrade.

So the question is where to tackle first now that I have established the unit when NEW had adequate delta T? Should I still go check it at the plenum (I assume I'd need to also make a hole to properly do it...knowing everything used to be fine, is that still necessary?)

 

[BrandonV]

Honestly at this point I think you just need to have someone check the system pressures.

This sounds like a classic refrigerant leak.

 

[ps2cho]

Honestly at this point I think you just need to have someone check the system pressures.

This sounds like a classic refrigerant leak.

I agree - but since I have two units, and both are exhibiting the same loss in delta T, it seems really unlikely that BOTH units have the exact same leak...since I had the house units installed I got the 608 license, installed my own mini split in a different room and have a little more experience so I'm going to get the subcooling checked regardless as I'd like the practice. Just ordered some thermocouplers to get a better reading.