Cannot bring down indoor t -Carrier Infinity

[crayx4]

My unit is a Carrier 2ton with 3 ton furnace, Infinity.
Was told that Delta t measured in the coil is 25, and subcooling 12 while super heat 10 and all looks normal according to tech for pressure/charge.

However, unit doesn't cool down more than 16-17 deg from what system shows external temperature to be.. At outdoor 95, it was not going below 79 even when set at 74.

Tech. thought there was a CFM issue as the system showed 700 even when on HIGH (whereas tech said it should call for 800. Tech goes up to the attic, touches some jumpers and now the system at high does go up to 800 and goes down to around 660 in dehum. mode.
HOWEVER, system doesn't appear to cool much better!

Static pressure has always been below 0.4 Humidity control has always been great too.

I am pretty sure tonnage is not an issue as it was the same as previous unit that was working just fine. Any idea of what it could be?

Not sure if it's relevant (tech seemed to think it isn't) but the log shows a "low pressure switch open" even back in March.

.

[mason]

You could check the return temp at the unit vs the return temp at the return grill. If the return runs through the attic and is leaking(hot air being sucked in) this could cause load problems on the evap coil. You could also check to make sure all the supply runs are hooked up correctly, just because it's moving 800 cfm doesn't mean it is making it to the rooms.

[mason]

Oh and by you I don't literally mean you but for you to have a professional who knows what to look for do the the work.

[tedkidd]

What do you program the stat to do? When you say "cool down", do you turn the system off?

Is it infinity stat? Infinity ac?

[crayx4]

Thanks for responding.

Infinity Stat. A/C 2 stage (24APA7) 6 months old


I meant, the system doesn't bring down the temperature to the set point...
It hits thermostat settings only at night or early morning. I leave thermostat "on hold" at 75 or 76 night and day, no programming..


What do you program the stat to do? When you say "cool down", do you turn the system off?

Is it infinity stat? Infinity ac?

[tedkidd]

System in unconditioned attic?

[mchild]

Supply side leak(s) would help keep static pressure low and also reduce the cooling effect as the cool air is being dumped into the attic. Plus this would put the house under negative pressure because the return is pulling air from the home. The negative pressure would increase the infiltration of hot air and often one of the easiest paths for air being pulled into the home is from the attic - which of course is the hottest air.

[tedkidd]

Let's slow down and not jump in with answers before we know the situation. Sounds like operator error is not causal, but education may still benefit.

Step back, get a big picture view, bring the homeowner into the science, THEN narrow in on culprits.

If we jump to obvious deficiencies often we come up with less than comprehensive solutions. Possibly walking by ancillary issues that combine with the primary problem. If they are going to fix one thing and be right next to another, might as well kill both problems, eh?

[crayx4]

It is indeed. As was the previous unit.


System in unconditioned attic?

[crayx4]

Tech stuck a thermometer in the insulation of the return and in one of the supply ducts (both near the furnace) and told me that the drop was 25 deg.

Supply ducts are all hooked to the furnace, not sure if you mean they may be unhooked near the grille? Not sure how they connect inside the grills...



You could check the return temp at the unit vs the return temp at the return grill. If the return runs through the attic and is leaking(hot air being sucked in) this could cause load problems on the evap coil. You could also check to make sure all the supply runs are hooked up correctly, just because it's moving 800 cfm doesn't mean it is making it to the rooms.

[crayx4]

How would they check for supply side leak and/or negative pressure? They didn't mention any of those.

When they installed the system they added two return grilles (12x12 kind of) in two different rooms.. Elsewhere I had asked if this was a minus, and pretty much everyone seemed to agree that more return is better.
I don't know before Infinity, but after it got installed my static pressure during cooling never showed more than 0.4 and during heating maybe 0.6




Supply side leak(s) would help keep static pressure low and also reduce the cooling effect as the cool air is being dumped into the attic. Plus this would put the house under negative pressure because the return is pulling air from the home. The negative pressure would increase the infiltration of hot air and often one of the easiest paths for air being pulled into the home is from the attic - which of course is the hottest air.

[crayx4]

by the way, last I checked the ducts were all sealed very well and there was no apparent leak AT ALL, in the attic. I think they did a pretty professional job on that front... Can check again if necessary, but when tech went up to inspect, he didn't mention any problem of that sort


You could check the return temp at the unit vs the return temp at the return grill. If the return runs through the attic and is leaking(hot air being sucked in) this could cause load problems on the evap coil. You could also check to make sure all the supply runs are hooked up correctly, just because it's moving 800 cfm doesn't mean it is making it to the rooms.

[mason]

by the way, last I checked the ducts were all sealed very well and there was no apparent leak AT ALL, in the attic. I think they did a pretty professional job on that front... Can check again if necessary, but when tech went up to inspect, he didn't mention any problem of that sort

I'm not implying that they were unprofessional, even the best make mistakes from time to time. I'm sure I'm not the first one to go back and find that a flex run/return slipped off the collar. I'm just pointing it out because it's a very easy thing for a tech to check. If there is a big difference in temps at the grilles from what he measured at the unit then that would be a problem. As someone else mentioned there are many more factors to consider in this situation but temp checks is an easy thing to do and if noone checks then you don't really know how the ductwork is performing.

[crayx4]

Will ask him to check temp at all grilles, vs. temp at furnace level.
I remember that when he installed the system he had said that temp at the grilles was not representative of real temp or temp drop in the unit...

IS 25 an average/good drop between return and supply near the furnace?
What I noticed was that the return temp. was much higher than the actual temperature in the house, but that may have been because the measurement was taken in the attic...

I think the technician's first thought was to check why the unit wasn't pushing more than 700 CFM when on HIGH, while product manual suggests the unit should go up to 800 CFM in that setting..
But now that it is pushing 800 CFM, it appears to me that 100 CFM more is not making a huge difference. I've just checked at T-stat is showing 78 when asking for 75 on external of 98 (coil temp 97). Static at 0.39



I'm not implying that they were unprofessional, even the best make mistakes from time to time. I'm sure I'm not the first one to go back and find that a flex run/return slipped off the collar. I'm just pointing it out because it's a very easy thing for a tech to check. If there is a big difference in temps at the grilles from what he measured at the unit then that would be a problem. As someone else mentioned there are many more factors to consider in this situation but temp checks is an easy thing to do and if noone checks then you don't really know how the ductwork is performing.

[mike_home]

Has the tech verified the compressor is operating in the high stage? Your fan is moving 800 CFM of air, but how do you know the compressor is moving from the low to high stage?

Did the Infinity controller displaying any error codes? This may indicate a problem.

This is a new installation. How is the contractor responding to the problem?

[mason]

Crayx4, when you say the return temp was much higher than the temp in the house how much higher are we talking about? 5,10,15,20+?

[catmanacman]

a 25 degree temp drop in a warm house is a sign that there is a low air flow issue also on the infinity system there is a air flow setting for comfort and efficiency set it to efficiency. also just because it is a 2 ton just like the other one does not mean anything , some 2 ton systems are 26000 btus and some 2 tons are 22000 btu

[crayx4]

Point well taken on the BTU, I didn't know that. I thought 2 ton is 2 ton.
That said, Manual J said that this system should work but obviously it isn't...

Sorry, did you say set the system to efficiency? I can try that, but how come comfort wouldn't work to hit my temp requirement?


What's a "normal" temp drop ?



a 25 degree temp drop in a warm house is a sign that there is a low air flow issue also on the infinity system there is a air flow setting for comfort and efficiency set it to efficiency. also just because it is a 2 ton just like the other one does not mean anything , some 2 ton systems are 26000 btus and some 2 tons are 22000 btu

[crayx4]

I think it was 90. I mean, when the shoved his thermometer inside the return insulation in the attic...

Indoor temp at the t-stat was 79 or there about.



Crayx4, when you say the return temp was much higher than the temp in the house how much higher are we talking about? 5,10,15,20+?

[crayx4]

1/ I think he did verify the compressor is operating high stage by looking at the Infinity controller.. Not sure if any other way of checking that he could have checked..
He did check the subcooling/superheat and he said they were perfect, 12 and 10 deg respectively I think
By the way, Infinity controller measures compressor RPM, is that linked to the stage? I can check that

2/ The only error code displayed was from March and shows "Low pressure Switch Open". Tech didn't comment on that and I forgot to ask what that mean.

3/Tech was convinced the issue was with CFM not going up to maximum even in high stage. So he got that fixed and now machine does go to 400 CFM/ton in high stage. But last I checked temp was 78 with outside 93, and t-stat calling for 75... This was at 19:00. Check my previous messages for temps at around lunchtime..
He told me unit should be ok now and to call him back on Mon to report after giving the cooler a couple of days.. I will check how it goes tomorrow, but it doesn't seem to be much better so far!



Has the tech verified the compressor is operating in the high stage? Your fan is moving 800 CFM of air, but how do you know the compressor is moving from the low to high stage?

Did the Infinity controller displaying any error codes? This may indicate a problem.

This is a new installation. How is the contractor responding to the problem?

[rickboggs]

If your unit is sized right it's sized to keep up not catch up. If you fall behind at capacity conditions, it will take a long while to catch up....you know... by morning.

I'm leaning towards low cfm, that's why the low pressure fault, and the 25 degree difference across the coil. Low cfm, the capacity goes way down and off on low pressure means no capacity... it's off.

But I don't know much about those units, so I may be just muddying the water.

[crayx4]

Appreciate your opinion.
Don't worry about muddying water up, I just want to be able to speak intelligently and ask the right questions to my contractor. Tech will take care of the situation, no matter what! I didn't pay top bucks for not working, but I want to try to understand if he understands the situation! From your comment he seemed to be on track. Will 100 CFM make a huge difference though?

When unit was not revving up, it was still at 700 CFM or so the stat showed...



If your unit is sized right it's sized to keep up not catch up. If you fall behind at capacity conditions, it will take a long while to catch up....you know... by morning.

I'm leaning towards low cfm, that's why the low pressure fault, and the 25 degree difference across the coil. Low cfm, the capacity goes way down and off on low pressure means no capacity... it's off.

But I don't know much about those units, so I may be just muddying the water.

[tedkidd]

A ductblaster test will determine duct leakage.

Having your equipment and ductwork in your superheated attic is problemmatic. Would you consider redefining your thermal boundary? Spraying 3" of closed cell foam to your roof deck would likely cure all your comfort troubles AND lower hvac costs.

[crayx4]

Tedkidd after buying that unit, not much $$ left!
And I don't understand why my 11y old Trane XE1200 2 ton was doing just fine!

Update at midnight: outside temp at 83 and stat still not going below 76!! Humidity is at 44% and rooms feel very comfortable though... System still showing 800 CFM and high stage.. Shouldn't the system adjust CFM up or down?? It never seem to move from 800 now!

Not sure what's going on, but I am not a happy camper...



QUOTE=tedkidd;10434322]A ductblaster test will determine duct leakage.

Having your equipment and ductwork in your superheated attic is problemmatic. Would you consider redefining your thermal boundary? Spraying 3" of closed cell foam to your roof deck would likely cure all your comfort troubles AND lower hvac costs.[/QUOTE]

[mike_home]

Can you post the model number of the condenser, coil, and furnace? The high stage CFM specified by Carrier can verified from the product data literature.

[crayx4]

24ANA124A003

CSPHP2412ATA

58CVA070-1-12



Can you post the model number of the condenser, coil, and furnace? The high stage CFM specified by Carrier can verified from the product data literature.

[mike_home]

24ANA124A003

CSPHP2412ATA

58CVA070-1-12

This is what is listed in the Product Data for the 24ANA1 condenser:

Condenser: 24ANA12430
Coil: CSPH*2412A** Furnance: 58CV(A,X)070---12

High 800CFM Low 800CFM
High Capacity: 25,600BTU Low Capacity: 19,800

SEER: 18.5 EER: 13.5

It appears 800CFM is corrct. What is interesting it is the same for both high and low cooling. This is also the air flow with any matched furnace or coil with this condenser. This seems to be only for the 2 ton condernser. The 3, 4, and 5 ton condensers use different CFMs for high and low.

Keep us posted on the progress. This is an interesting problem. I hope the contractor resolves this soon.

[egads]

In your first post you state that the tech "went up into the attic and touched some jumpers" to try and address the problems. It is my understanding (as a fellow homeowner) that the Infinity system should control itself. A tech does not adjust jumpers to control the fan speed. Your furnace has a variable speed motor that is controlled by an electronic logic circuit board. I am going to suggest you have your tech call Carrier tech support and have them walk him through some trouble shooting.

This would be in addition to having the (original ducts?) tested for leaks. Infinity variable speed fans do weird things with bad ducts.

[crayx4]

That's correct. Under the direction of Carrier support, he changed a switch. He told me that the controller will override that switch anyway, but doing that seemed to "unstuck" the system from the 700 CFM it was at.. Now the unit ramps to 800 CFM in high stage and A/C control set on HIGH(haven't noticed low stage yet). When in COMFORT control, unit shows upper 600s (not sure if compressor is then in low stage or high stage.. I assume all dehumid functions operate in low stage by definition).


I don't have a clue if the unit would move away from 800 CFM in high stage.

Last check at 14:30. Ext temp: 99 Internal temp: 78, requesting 73



In your first post you state that the tech "went up into the attic and touched some jumpers" to try and address the problems. It is my understanding (as a fellow homeowner) that the Infinity
system should control itself. A tech does not adjust jumpers to control the fan speed. Your furnace has a variable speed motor that is controlled by an electronic logic circuit board. I am going to suggest you have your tech call Carrier tech support and have them walk him through some trouble shooting.

This would be in addition to having the (original ducts?) tested for leaks. Infinity variable speed fans do weird things with bad ducts.

[crayx4]

Sorry copied wrong data:
Compressor is 24APA724A ! My bad
Furnace is correct


This is what is listed in the Product Data for the 24ANA1 condenser:

Condenser: 24ANA12430
Coil: CSPH*2412A** Furnance: 58CV(A,X)070---12

High 800CFM Low 800CFM
High Capacity: 25,600BTU Low Capacity: 19,800

SEER: 18.5 EER: 13.5

It appears 800CFM is corrct. What is interesting it is the same for both high and low cooling. This is also the air flow with any matched furnace or coil with this condenser. This seems to be only for the 2 ton condernser. The 3, 4, and 5 ton condensers use different CFMs for high and low.

Keep us posted on the progress. This is an interesting problem. I hope the contractor resolves this soon.

[mike_home]

Sorry copied wrong data:
Compressor is 24APA724A ! My bad
Furnace is correct

The numbers for the Performance condenser are different. Here is the AHRI match. The CFMs for high and low are 660 and 530 respectively.

3483754 24APA724A30 CSPH*2412A**+UI 58CV(A,X)070---12 24,800 20,400 13.0 16.0 660 530

I am not a Pro, but I don't think the problem is related to the air flow.

[crayx4]

I am with you... but I am no pro either, and I let the tech do his work..

What's the implication of increasing CFM to 800 if the high setting is actually 660?? Will it do any good, or more damage (worse humidity control, lower capacity, I don't know...) than good???



The numbers for the Performance condenser are different. Here is the AHRI match. The CFMs for high and low are 660 and 530 respectively.

3483754 24APA724A30 CSPH*2412A**+UI 58CV(A,X)070---12 24,800 20,400 13.0 16.0 660 530

I am not a Pro, but I don't think the problem is related to the air flow.

[cuchulain]

if it's not rated for 800cfm and that's what you forced it up to, then yea it will hamper the system. It won't let the coil get cold enough, so basically you won't have cold air coming out of the system (or as cold as it can be).

[cuchulain]

if they cannot find the problem and are having to call tech support and still not finding the problem, have them request a tech support member come to the call with them. One of carrier's tech support facilities is right there in N.W. Houston, and I know most of them LOVE to go out and get their hands dirty every once in awhile. Esp if it's related to an infinity problem.

[crayx4]

great advise!

So normally my system should be able to hold 74-95 if outside temp is in the upper 90s?

Today's temps (external-internal)
14:00 98-78
15:00 99-79
16:00 103-79
19:00 94-80
20:30 90-79

Look normal, if sized correctly and no airflow issue??


if they cannot find the problem and are having to call tech support and still not finding the problem, have them request a tech support member come to the call with them. One of carrier's tech support facilities is right there in N.W. Houston, and I know most of them LOVE to go out and get their hands dirty every once in awhile. Esp if it's related to an infinity problem.

[cuchulain]

If the unit is sized correctly, ALL the way around...ie R/A, S/A, lineset, as well as unit size. then yes a 74 degree temp is obtainable. If you have the dehumidification set up on the infinity you should be able to keep it a bit higher even and have it quite comfortable. I keep my stat right around the 77 mark and it's quite comfortable in the house cause of the dehumidification. Email me with the company you are using and what area of town you are in and i may be able to offer a better company. my email is in my profile.

[crayx4]

Thanks for your offer, but as I bought >1y ago from these guys and got a 10y extended Labor and Parts warranty.. I'll have to stick to them. I am sure they will make things right sooner or later. I was just trying to see if they were probing in the right direction....


If the unit is sized correctly, ALL the way around...ie R/A, S/A, lineset, as well as unit size. then yes a 74 degree temp is obtainable. If you have the dehumidification set up on the infinity you should be able to keep it a bit higher even and have it quite comfortable. I keep my stat right around the 77 mark and it's quite comfortable in the house cause of the dehumidification. Email me with the company you are using and what area of town you are in and i may be able to offer a better company. my email is in my profile.

[cuchulain]

you do NOT have to stick with them just cause you ahve the 10y warranty (unless it's through them). If it's the carrier warranty, then any carrier dealer can handle it. You just have to provide them with a copy of the warranty agreement.

[DOGBOY]

If the unit is sized correctly, ALL the way around...ie R/A, S/A, lineset, as well as unit size. then yes a 74 degree temp is obtainable.

so at what max outdoor temp will he be able to maintain his desired 74*? I was always told 20* cooler indoors than outdoors at a design temp. I know different areas use different temps. And every where iv'e been it was usually in the low 90's.

My thought is if you have a 25* td inside then you probably need more airflow and it will help the system to reach desired temperature by circulating more air and in turn cooling more air. And no, you will not mess up the system or have a humidtiy problem as the td is too high at 25*. If the td was closer to 10* then you would not need more air and you will not remove enough humidity.

I have seen many attics getting too hot causing the unit not to keep up with the heat load. This is both with the system and duct work in the attic and just heat being transfered through the ceiling.

and I am assuming external = outdoor and internal = indoor. :.02:

dogboy

[crayx4]

It is the Carrier warranty. Really? My understanding was that the other dealer can choose whether to pick up your warranty or not, basically they are not obliged to. Not sure if that means like "take over" for the remainder of the 10 years, or on a case by case (something breaks and I can call whomever to get it fixed..)



you do NOT have to stick with them just cause you ahve the 10y warranty (unless it's through them). If it's the carrier warranty, then any carrier dealer can handle it. You just have to provide them with a copy of the warranty agreement.

[egads]

Just like with automobile extended warranties, HVAC ones should always be factory ones.

Now in your case, with Carrier, they will get your tech up to speed on this or he will no longer be a Carrier dealer. Carrier wants you happy.

If you have airflow issues and addressing them was not part of your original contract, you would have to pay for changes.

I have a customer who had Carrier Infinity issues. I helped her find a different contractor who addressed duct issues. There is a night and day difference in how it works now. We just had to give up on the installing contractor.

[crayx4]

Thanks Dogboy, I think you are saying what my tech was saying... but still sometimes the system cannot achieve even 20 deg. below outdoor temperature for whatever reason... See post above for today's readings..


so at what max outdoor temp will he be able to maintain his desired 74*? I was always told 20* cooler indoors than outdoors at a design temp. I know different areas use different temps. And every where iv'e been it was usually in the low 90's.

My thought is if you have a 25* td inside then you probably need more airflow and it will help the system to reach desired temperature by circulating more air and in turn cooling more air. And no, you will not mess up the system or have a humidtiy problem as the td is too high at 25*. If the td was closer to 10* then you would not need more air and you will not remove enough humidity.

I have seen many attics getting too hot causing the unit not to keep up with the heat load. This is both with the system and duct work in the attic and just heat being transfered through the ceiling.

and I am assuming external = outdoor and internal = indoor. :.02:

dogboy

[cuchulain]

it's not a "whomever" it will have to be a carrier dealer. It is like taking the warranty over from the company you currently have. A reputable dealer wouldn't balk at taking it over. They do the work, submit the warranty paperwork to carrier they get paid. Simple. I really wouldn't recommend calling a different company for each problem, but find a company that is able to handle the problem and stick with them. apparently this company can't handle the problem so it's time to move on.

[cuchulain]

dogboy obtaining the 74 shouldn't be much of a problem if the install was done correctly. I replaced my system 3 yrs ago in November, It's not an infinity, but a nordyne iq. I can set it to pretty much whatever I want and have no problems reaching the temp no matter the the outside. temp. After I believe 95 degrees (i know someone can confirm the temp number) the system does start to lose capacity, but it shouldn't be enough that he's not reaching the temps he's hoping for.

[DOGBOY]

dogboy obtaining the 74 shouldn't be much of a problem if the install was done correctly. I replaced my system 3 yrs ago in November, It's not an infinity, but a nordyne iq. I can set it to pretty much whatever I want and have no problems reaching the temp no matter the the outside. temp. After I believe 95 degrees (i know someone can confirm the temp number) the system does start to lose capacity, but it shouldn't be enough that he's not reaching the temps he's hoping for.

So what you are saying is if it is 100* outside he should be able to reach 74* with no problem at all? So evidentilly I know nothing about losing capacity as I thought losing capacity meant something like this. 3 ton a/c running at a lower capacity is now equal to 2 1/2 or 2 tons of cooling. Now this smaller a/c is trying to cool a space that is too large for it and it can do it?

I can understand your theory if the unit was oversized and as it loses capacity it is now sized properly.

And I am not saying he should not be able to reach his desired temp but there is a balance point and as I stated earlier I don't know what that number is for his area. You could be right and it is 95*.

So could you answer me this? with his t-stat set at 74* what is the maximum temp outside that he can reach his desired set point? 94*, 104*, 114*?

evidently if it is properly/correctly installed it should reach his set point at any outside temp.

dogboy

[cuchulain]

Dogboy, i live 60miles S of him. (maybe more depending on what side of town) and right after i installed my system we redid the floors and kitchen. The guys doing it had both back and front door open (they were bringing stuff in the front door and cutting it on the back porch) they had the stat set at 60 degrees all day, when I got home it was in the 65 degree area. Like that every day for a week. They did this end of march first part of june when temps were in the 90's. It ran all day long at max capacity, but it did do it.

We have a couple of customers who have the infinity system (including one of our techs). I know the one at the techs house maintains 75 all year round. Another of those customers maintains his at 73.

We routinely have customers setting their stats between the 70-75 degree range, and the units that are installed correctly cycle off routinely. It all goes back to the installation and design conditions.

[DOGBOY]

It all goes back to the installation and design conditions.

Design conditions. What temp are you using? Now I have to admit I do not do any load calculations since I was in school so I am very ignorant on that subject. However I was told in school that an a/c will cool down the conditioned space only 20* cooler than outside temps. This is providing that it is sized properly. Am I wrong?
And there are of course other factors that can affect this. the main one I see affecting this is attic temps.


dogboy

[rickboggs]

Design conditions. What temp are you using? Now I have to admit I do not do any load calculations since I was in school so I am very ignorant on that subject. However I was told in school that an a/c will cool down the conditioned space only 20* cooler than outside temps. This is providing that it is sized properly. Am I wrong?
And there are of course other factors that can affect this. the main one I see affecting this is attic temps.


dogboyWhat if the weather data for my neck of the woods says my outside conditions are 93 degrees and I want 75 degree indoors with 50% relative humidity of course. That's only 18 degrees difference. What if the weather data says 100 degrees? 25 degree difference.

[tedkidd]

A house is like a toilet tank with a leak, where the hotter it gets the bigger the leak. Your ac is like the valve, keeping the tank full.

Seems some think if they come home and the tank isn't full the only place the problem could be is the valve. But if that's all you have capacity to consider and that's not it, you are beating your head against a wall. Imagine blaming the air compressor for the tire that won't hold pressure. You have a problem with your tire, must be the compressors fault? Maybe, but if you don't look at the whole system, what do you know? I recognoze ignorance is bliss, but it also misses opportunities.

An energy audit is like a physical for your home. People are AMAZED at the things they learn about their homes, and the opportunities for cost effective improvements to comfort and energy reduction. Ever had one? House doesn't need to be obviously sick to have one, but when it is sick the justification jumps to 100%.

Cuch, if you didn't have an inverter system, that performance would indicate grossly oversized. Not sure it makes the right point about anything, other than inverter driven is clearly the way to go for this decade.

[crayx4]

Great question! and exactly what I'd like to know myself..

What I find baffling is that during the peak of the day (outside 102-103) the delta-t is more around 23 sometimes 24 deg. BUT when the temp. goes down to 85-86 at night, the system appears to struggle to keep 8 deg of delta-t !!!






So could you answer me this? with his t-stat set at 74* what is the maximum temp outside that he can reach his desired set point? 94*, 104*, 114*?

evidently if it is properly/correctly installed it should reach his set point at any outside temp.

dogboy

[crayx4]

Your logic is faultless, however in my case, house was fine with previous old 2t unit.. And now it isn't... Nothing has changed in the house, other than I keep my ground floor unit at even lower temp now to try to help out..


A house is like a toilet tank with a leak, where the hotter it gets the bigger the leak. Your ac is like the valve, keeping the tank full.

[BigD629]

I'm not a pro, but the same thing happened to me. I replaced a 3 ton with a 3 ton Carrier infinity furnace and Performance HP. Same issue's. To make a long story short, I ended up having it replaced with the exact same equipment except a 3.5 ton HP. Now it works as I thought it should. It will now maintain 72-74 on even the hottest days. My humidity stays at 48% or less and the unit cycles normally. If they can't find anything wrong and say it's operating normally, then it's a logical conclusion that it might just be undersized?

[mason]

I think it was 90. I mean, when the shoved his thermometer inside the return insulation in the attic...

Indoor temp at the t-stat was 79 or there about.

Crayx4, I checked three units today during my diagnostics just to give you some real world data. All three were units that I confirmed the return had been properly sized and installed, they all had return duct in attic. Average attic temp was 109. Unit one, room temp=72, return at unit=72.6. unit 2, room temp=78, return temp=79. unit 3, room temp 76, return temp=76. If your getting 11+ gain in return temp from room to unit then you have a problem with your return duct. You should confirm those numbers, 90 and 79.

[crayx4]

Mason, thx for the note. I'll have to check with the tech if he remembers what he said the RA temp was..
That said, your attic temps are probably 20 deg lower than mine although I never measured it to be sure..


Crayx4, I checked three units today during my diagnostics just to give you some real world data. All three were units that I confirmed the return had been properly sized and installed, they all had return duct in attic. Average attic temp was 109. Unit one, room temp=72, return at unit=72.6. unit 2, room temp=78, return temp=79. unit 3, room temp 76, return temp=76. If your getting 11+ gain in return temp from room to unit then you have a problem with your return duct. You should confirm those numbers, 90 and 79.