New system not much different than 25-yr old system, help!

[grandtiger]

Hi all,

I am new to this forum. I recently have a new A/C system installed. However, it performs only marginally better than my 25-year old system, which is replaced by the new one.

It suffers the same problems with my old system:
1. Cool very slowly. The indoor temperature only drop 4F after running 3~4 hours
2. Runs 19~20 hours a day, when the ourdoor tempearture is 90~72F range and indoor temp is set to 75F, and it can not maintain the target temperature after 10:30AM the next day (the minimum it can maintain is 76F) and run continuously from 2:30PM till midnight, and from 10:00AM till 5:00PM the next day (I stop the system after that)

I observed pretty much the whol installation process and after I received manuals and read it later on, I found the following steps specified in installer's guide are skipped, which may be the root cause of the problem:
1. No Leak Check
2. No System Evacuation
3. No operational testing (air temperature, refrigerant pressure, outdoor air temp, etc) and I am not sure the freon is properly charged

I know skipping those steps are no good, can anyone point me to some resources that can prove how bad it can be?

Additionally, what is your typical experience of your A/C system? And what is your expectation of a new system? Specifically:
1. how long do you expect your room temp to drop to a comfortable level after you turn on A/C on an average summer day?
2. how long do you expect your room temp to reach your target temp and your A/C goes to an on/off cycle?
3. how many degree F do you expect your A/C system to be able to drop compare to an outdoor temperature of 91 degree F?
4. How many hours do you expect your A/C system to run on an average summer day (say outdoor temp between 72~91F, target temp set to 75F) if it's properly sized?
5. On the hottest day, how many degree F can your A/C drop compare to outdoor temperature?

Thanks in advance for any information and any advise on how to fix the problem.

[Edited by grandtiger on 07-10-2006 at 10:31 AM]

[grandtiger]

deleted

[Edited by grandtiger on 07-10-2006 at 10:24 AM]

[mjk_na]

grandtiger,

Did you check on how did the person perform load calculation, and calculation for ductwork?

1. About 3-5 minutes.
2. Depends on the set temperature. Lower set temperature will require it to run longer.
3. about 20-25 degrees F.
4. You mean the compressor? See (2).
5. Mine is sized properly. It can keep my room at 16 degrees C, even during hottest days (35 degrees C).

[pstu]

I am a homeowner not a pro. Why don't you try just calling the installing company and tell them you are not satisfied? You expected the new system to pull down temperatures better than the old one, and to run less. That does not guarantee you good results, but it follows good business manners to give the original guy(s) a chance to set things right.

You should NOT have to defend yourself, and I think it a mistake to try to dissect what they should have done and argue those details with them. Save that for later if really necessary. I think it's a mistake to try to look for proof that what they left out, has bad consequences. Your AC cooling your house (with good humidity control) and running for years without breaking is the main proof. If they were hacks, you may not get very far with them, but you gotta try.

Most of your questions about performance are very dependent on sizing. A system sized properly according to ACCA Manual J, as I understand is expected to run several hours nonstop during the hotter days, and perhaps to not maintain the thermostat setpoint for brief periods in the hottest days. Very few systems are actually undersized, if yours fails to perform then there is probably another problem to fix.

During the Manual J sizing model, you are asked to input design conditions for indoors and outdoors. So there is no one answer to your question about holding X degrees below outdoor. My own design conditions assume 94 to 99 outside and 75 inside. The 94 outdoor temp is recommended by the software, I did a cheat up to 99 because of remembering 1980 which had many 100+ days. My system has been observed to run 2-3 hours nonstop and I believe I want to not exceed that number -- just my opinion not a pro's judgement.

It would be very useful to ask the techs to check your "External Static Pressure" (ESP) and your airflows if they have that capability. That may reveal an airflow problem which is keeping your system from putting out as many cooling BTUs as it should. If your old tech fails to satisfy, I would consider one trained by the National Comfort Institute:
http://www.nationalcomfortinstitute.com/

You say you are not sure the freon is properly charged. Is it your job to be sure of that, or the tech's? I think that you should be working with a company you can trust, rather than trying to second guess them. Those other steps you say were not done, you have a legitimate thing to discuss with your AC company, just do it. Perhaps ask for the manager rather than the installing tech.

I think it best to work as much as you can with the original AC company, there must have been some good reason you chose them. Sometimes you can get the AC manufacturer to work with you and that company to try to get a quality install. Even if you have to go to a 2nd AC company to set things right, you gotta do what you gotta do.

Best of luck -- Pstu

P.S. On this board you can edit your post if you want, rather than adding a second one right after.

[grandtiger]

Hi mjk_na,

Thanks for your reply.

As for the size/capacity, I believe it's enough and properly slightly oversized. I have a two-bedroom condo at the third (top) floor with 1100 sq.ft. and the system is a two-ton (24,000BTU) system. I got free esitimates from about 5 contractors, and they all quotes the same size.

The system was first started around 2:30PM when outdoor temp was 91F (the highest temp of the day, after that it slowly decline to 90, 88 and 87 by 5:30PM), and the target temp is set to 75F and indoor temp was 85F. Do you think this is normal for a new system?

[BaldLoonie]

A/C units are good at maintaining but try to get them to drop a hot place on a hot day and good luck. My unit will let me hang meat even in 90+ steamy weather but only if it starts out cool. A week ago on a hot day, I opened the house first thing in the morning to air it out. But was gone until mid afternoon and the house got up to 81. It took 12 hours to get the house back to 70 and that was because it really cooled down outside after sunset. If I had left the unit on and windows closed, it would have had no trouble holding 70.

If you are in the 90s, you may not get it to drop much but should maintain mid 70s running constantly as long as you don't let it warm up then turn it down.

[grandtiger]

Hi pstu,
Thanks a lot for your advice.
However, the reason that I asked for help here is because I can not get help from the company that installed the system.
They tried to avoid me, they denied any wrong-doing, I left them messages described the problem of the system, but they did not listen to them carefully and never call me back and discuss the problem, and even when I spoke to the owner, he never let me speak instead blame me being nasty and mean and hung up on me. They keep making untruthful claims that they gave me first-class system, they did first-class job, and the reality is that they did not even follow the manufacturer installer's guide.
I guess I didn't do enough research and I am too naive as an immigrant expecting much better things in the America. They also appears to discriminate against me.
I know they did not install the system properly, but I don't know how to fight and win this war.
Anyone has similar experience or know what's the right thing to do, please help!!!


Originally posted by pstu
I am a homeowner not a pro. Why don't you try just calling the installing company and tell them you are not satisfied? You expected the new system to pull down temperatures better than the old one, and to run less. That does not guarantee you good results, but it follows good business manners to give the original guy(s) a chance to set things right.

You should NOT have to defend yourself, and I think it a mistake to try to dissect what they should have done and argue those details with them. Save that for later if really necessary. I think it's a mistake to try to look for proof that what they left out, has bad consequences. Your AC cooling your house (with good humidity control) and running for years without breaking is the main proof. If they were hacks, you may not get very far with them, but you gotta try.

Most of your questions about performance are very dependent on sizing. A system sized properly according to ACCA Manual J, as I understand is expected to run several hours nonstop during the hotter days, and perhaps to not maintain the thermostat setpoint for brief periods in the hottest days. Very few systems are actually undersized, if yours fails to perform then there is probably another problem to fix.

During the Manual J sizing model, you are asked to input design conditions for indoors and outdoors. So there is no one answer to your question about holding X degrees below outdoor. My own design conditions assume 94 to 99 outside and 75 inside. The 94 outdoor temp is recommended by the software, I did a cheat up to 99 because of remembering 1980 which had many 100+ days. My system has been observed to run 2-3 hours nonstop and I believe I want to not exceed that number -- just my opinion not a pro's judgement.

It would be very useful to ask the techs to check your "External Static Pressure" (ESP) and your airflows if they have that capability. That may reveal an airflow problem which is keeping your system from putting out as many cooling BTUs as it should. If your old tech fails to satisfy, I would consider one trained by the National Comfort Institute:
http://www.nationalcomfortinstitute.com/

You say you are not sure the freon is properly charged. Is it your job to be sure of that, or the tech's? I think that you should be working with a company you can trust, rather than trying to second guess them. Those other steps you say were not done, you have a legitimate thing to discuss with your AC company, just do it. Perhaps ask for the manager rather than the installing tech.

I think it best to work as much as you can with the original AC company, there must have been some good reason you chose them. Sometimes you can get the AC manufacturer to work with you and that company to try to get a quality install. Even if you have to go to a 2nd AC company to set things right, you gotta do what you gotta do.

Best of luck -- Pstu

P.S. On this board you can edit your post if you want, rather than adding a second one right after.

[mayguy]

The system was first started around 2:30PM when outdoor temp was 91F (the highest temp of the day, after that it slowly decline to 90, 88 and 87 by 5:30PM), and the target temp is set to 75F and indoor temp was 85F. Do you think this is normal for a new system?

That's your problem!


If you know for a fact fit the day time temp is going to be hot, start the unit in the moring or the day before! Once it's on, set it and forget it.

A/C does not pull the temp down fast like a heating system does.

[rickboggs]

System Evacuation
operational testing (we just call it start up) you may have some problems, but a unit sized proper will KEEP UP not CATCH UP at load conditions

If the equipment is sized for 93 degrees outdoor and 75 degree indoor and it IS 93 outside and you have controls set at 75 the equipment will not stop running until it is cooler outside or you set the controls higher inside.

[danglerb]

The installation is done, nothing is likely actually "wrong" with it, and almost certainly nothing is going to be done by the contractor to materially change its operation.

Condos are notorious for problems, insulation not really as good as it should be, not sealed as well as it should be, and three levels are difficult to manage temperatures in anyway.

Before the install you should have required the contractor to do a heat load calculation, but its very common that contractors skip that unless requested when replacing a system.

Many consumers get efficiency and capacity mixed up. Your new unit is almost certainly the same capacity as the old one, and cools no better or worse than the old one. The increased efficiency doesn't make it cool any better, in some cases not as well, but to operate using less power.

Set the thermostat to 75 and leave it on and see if it can hold that temperature.

[thomefan2579]

sounds like nothing is wrong and how do you know that they skipped these steps were you over their shoulder the whole time i sure hope for there sake you were not. operation sounds normala nd to get proper dehumidification long runs cycles are the norm. i would first relx turn the stat to 75 walk away and if she holds 75 on a hot day and turns off at least a little bit relax there is more then likely no issue. If i was the contractor and some home owner who knows nothing says we didnt do things when i know my guys did I would be kinda upset as well. If you know so much why didnt you do it yourself. And save the contractor the hassel also to cut down on run time you coulda put in a 5 ton system it wount run very long but your house may feel like the rain forest

[grandtiger]

I got a few quotes and some did load calculation, so don't. Most of them agree that two-ton is slightly oversized, the old one is mostly likely only 1.5 ton because it's used on both 1-bedroom and 2-bebroom units when the condos were built.

I do understand the difference between efficiency and capacity. And neither of them hold up to my expectation. I set target temp to 75F and kept the system running for 27.5 hours (2:30PM to 5:00PM the next day). It took 10 hours to get to the target running continuously, while the outdoor temp has dropped from 91F to 76F. But it can not hold that temperature the following day starting from 10:00AM, it started running continuously again. The on/off cycles only happened between mid-night and 10:00AM. I think it's very inefficient, only marginally improved compared to my 25-yr old system.


Originally posted by danglerb
The installation is done, nothing is likely actually "wrong" with it, and almost certainly nothing is going to be done by the contractor to materially change its operation.

Condos are notorious for problems, insulation not really as good as it should be, not sealed as well as it should be, and three levels are difficult to manage temperatures in anyway.

Before the install you should have required the contractor to do a heat load calculation, but its very common that contractors skip that unless requested when replacing a system.

Many consumers get efficiency and capacity mixed up. Your new unit is almost certainly the same capacity as the old one, and cools no better or worse than the old one. The increased efficiency doesn't make it cool any better, in some cases not as well, but to operate using less power.

Set the thermostat to 75 and leave it on and see if it can hold that temperature.

[thomefan2579]

youll probloy be surprised when you get your gas bill the system sounds like it runs like mine and is very effeicnt i set it for 70 all the time and have very low bills

[grandtiger]

Yes, I observed the whole installation process (literally over their shoulder most of the time). There are times that they tried to hide something from me and also I went away during the brazing because it smells bad. But certainly I know what major steps they skipped. Yes, I understood HVAC system quite well because I have a Bachelor's degree in HVAC&R, but I have moved on to different field since graduate school. I can certainly get a license/permit and buy all the equipment to install my own system. But that does not make sense economically.


Originally posted by thomefan2579
sounds like nothing is wrong and how do you know that they skipped these steps were you over their shoulder the whole time i sure hope for there sake you were not. operation sounds normala nd to get proper dehumidification long runs cycles are the norm. i would first relx turn the stat to 75 walk away and if she holds 75 on a hot day and turns off at least a little bit relax there is more then likely no issue. If i was the contractor and some home owner who knows nothing says we didnt do things when i know my guys did I would be kinda upset as well. If you know so much why didnt you do it yourself. And save the contractor the hassel also to cut down on run time you coulda put in a 5 ton system it wount run very long but your house may feel like the rain forest

[l•k]

what's your output airstream temp?

my window-shaker is putting out 58°
(outdoors is about 95°)
room temp is 79°

[grandtiger]

They didn't do any measurement after the installation, and I do not have the tools to test the output airstream temp. I could try to use a thermometer to measure the air temp of the closest outlet, but that is just a ballpark estimate.


Originally posted by l•k
what's your output airstream temp?

my window-shaker is putting out 58°
(outdoors is about 95°)
room temp is 79°

[thomefan2579]

did they weigh in charge or charge by superheat also did they pull a vaccum to 400 microns and let it hold? and i mean electric bill and not gas sorry. as far as a degree it really does not mean too much i know many Textbook techs who are horrible in the real world but they have a piece of paper that says they can pass a test

[HVAC/Stud]

What is the brand and model #?

Is the evap coil and condenser unit an ARI match?

What seer is the unit?

Was any check of the duct work done?

Is the duct work in an attic?

Where do you live?

STUD

[grandtiger]

During the whole process, no vacuum pump is used at all. They don't follow installer's guide to make sure it's properly charged. Unless they have some trick that we don't know, I don't think they have made any effort the ensure the system is properly charge. And by the way, a major leak was found when the refrigerant lines were connected and he redid the brazing.


Originally posted by thomefan2579
did they weigh in charge or charge by superheat also did they pull a vaccum to 400 microns and let it hold? and i mean electric bill and not gas sorry. as far as a degree it really does not mean too much i know many Textbook techs who are horrible in the real world but they have a piece of paper that says they can pass a test

[l•k]

http://usera.imagecave.com/threadbare/wallshaker.jpg

[BaldLoonie]

If you have any ducts outside the conditioned space, some simple temp readings make sense. Take 4.

Return air at the grille in the house
Return air at the inlet of the air handler

Is it different? Is the inlet temp higher than at the return grille(s)? If so you are picking up a lot of attic heat in the return. Either just from the intense attic heat radiating into the poor insulation of the flex or you have leaks sucking in hot air

Supply air a few feet from the outlet of the coil
Supply temp at some of the registers

Same point, heat gain in the supply will hurt. The thermometer won't tell of air leaking out.

We checked a house that wasn't cooling well when we swapped a 2 ton for a 2 ton. Air leaving the coil was 60, air coming out of his bedroom vents was 67. Main trunk ran 35' across the attic, had a internal liner but obviously that wasn't keeping out the extreme attic heat.

[thomefan2579]

ok my bad man sorry if they never used a vaccum pump you must have no condensibles in the lines they need to come out recover the charge pull a vaccum and recharge with new r22 if they wont help call the BBB and a company that has NATE certification or is highly reccomended in the area

[Irishmist]

Hello Eddy wannabe.

[grandtiger]

As you suggested, I measured the temperatures today.

The grille in the condo is the same as the inlet of the air handler. There is one and only inlet, so I don't need to compare the difference.

I measured the shortest outlet and the longest outlet in the house, the temperature difference is about 1F, I think that is normal and the problem most likely is not in the ducts but the cooling system.



Originally posted by BaldLoonie
If you have any ducts outside the conditioned space, some simple temp readings make sense. Take 4.

Return air at the grille in the house
Return air at the inlet of the air handler

Is it different? Is the inlet temp higher than at the return grille(s)? If so you are picking up a lot of attic heat in the return. Either just from the intense attic heat radiating into the poor insulation of the flex or you have leaks sucking in hot air

Supply air a few feet from the outlet of the coil
Supply temp at some of the registers

Same point, heat gain in the supply will hurt. The thermometer won't tell of air leaking out.

We checked a house that wasn't cooling well when we swapped a 2 ton for a 2 ton. Air leaving the coil was 60, air coming out of his bedroom vents was 67. Main trunk ran 35' across the attic, had a internal liner but obviously that wasn't keeping out the extreme attic heat.

[mayguy]

so what is the temp reading you've gotten?

[freddie]

Is this house 25 years old, Check to see if you have any insulation left in the ceiling, you may need to have some more blown, just an idea

[beshvac]

My comments:

1. Efficiency has nothing to do with how long the unit runs. Your 25 year old system had a low seer and your new one 10 seer plus.

2. Set the thermostat and forget it (was also good advice from another poster) IF you want to screw with the thermostat get a programmable one and set back a few degrees.

3. A properly sized system will not pull down temperature very fast on the hottest day. Qac - Qload = "thermal mass" X dT/dt At the hottest part of the year the capacity of the ac just meets the load therfore it won't be moving temperature all that quick. "set it and forget it" you wont save any money by shutting off the unit because when you turn it back on not only are you cooling the temperature of the air in the house but you also have to remove the heat on the "thermal mass" or in other words the heat contained in the building envelope and all the contents.

4. Did you go with the lowest bidder? If you did then dont' be surprized if they dont have a micron guage and dont pull a vacuum but purge the system. Get the system tuned by a reputable company to check the charge.

[danglerb]

How far up in the bids need one go to get basic competency? Somehow I think incompetence is available at a wide range of prices.

OP wasn't too clear about it, but it sounded like he said he left the system on with 75F set point for 27 hours and the system could not keep up as temperatures went up the second day.

Model numbers would be nice for this exercise.

What can the guy do though, the AC is in, and its too small, or not working well. Maybe the thing to do is verify its working properly first.

[grandtiger]

Because all the problems and concerns, I am not comfortable running the system. I only run it on very hot days (twice so far), therefore it's not possible to look at the bills to determine the efficiency. Plus, PSE&G does not always provide actually reading every months.


Originally posted by thomefan2579
youll probloy be surprised when you get your gas bill the system sounds like it runs like mine and is very effeicnt i set it for 70 all the time and have very low bills

[grandtiger]

1. Condenser - Trane XB13, 2-ton, 13 SEER
2. Evaporator Coil - ADP TE32436, 1.5-3 ton (www.adpnow.com)

No check of ductwork, they already exist for 25 years.

Yes, it's in an attic.

I live in central New Jersey.


Originally posted by HVAC/Stud
What is the brand and model #?

Is the evap coil and condenser unit an ARI match?

What seer is the unit?

Was any check of the duct work done?

Is the duct work in an attic?

Where do you live?

STUD

[grandtiger]

Started the system at 6:45PM outdoor temp 85F, indoor temp 86F.

around 7:15PM
outdoor temp 85F, indoor temp 85F
closest outlet air temp: 71F
farthest outlet air temp: 72F

around 7:45PM
outdoor temp 84F, indoor temp 84F
closest outlet air temp: 70F
farthest outlet air temp: 71F

around 8:15PM
outdoor temp 84F, indoor temp 83F
closest outlet air temp: 69F
farthest outlet air temp: 70F

around 8:45PM
outdoor temp 83F, indoor temp 82F
closest outlet air temp: 68F
farthest outlet air temp: 69F

I also measure the inlet air temp, it says 82F. I was a little puzzled why it has the same reading as thermostat. But I think of two possible explanations:
1. the thermostat is 6 ft up on the wall, but the inlet is close to the floor.
2. The reading comes from the two thermometers, and they may not agree exactly.

Before I shut down my system, I went out to balcony and put my hand over the condenser fan, the temperature of the air blowed out seems very close to air temperature. It seems to me that the cooling system is not very good at taking the heat out of my house.

Around 9:15PM, since the outdoor temp is the same as indoor temp, we shut down the system, opened all windows and just used fans instead.

This is a cooler day compared to the last run, and the result is very similar too.

Any insights?


Originally posted by mayguy
so what is the temp reading you've gotten?

[thomefan2579]

you are in some trouble why by the xb line the xr line is like 200 more and has double the warranty something sounds fishy this was the lowest bid correct and only 5 year compressor and coil warranty shoulda got the xr13 properly installed its also much quiter

[thomefan2579]

also can you get a temp on the return near the furnace and one just above the a coil so we can get a temp drop if your 18-20 degrees its working pretty dang good

[grandtiger]

You are right, this is the lowest bid. But I think the problem is not what kind of equipment you selected, but how the installation is done.


Originally posted by thomefan2579
you are in some trouble why by the xb line the xr line is like 200 more and has double the warranty something sounds fishy this was the lowest bid correct and only 5 year compressor and coil warranty shoulda got the xr13 properly installed its also much quiter

[grandtiger]

The inlet is less than one foot to the furnace, so the temp should be the same. However, I am not able to measure the temp just above the coil because it's closed.

Any suggestion to get a ballpark estimate? The closest outlet is about 9 ft from the coil and I measured the temp as in my previous post (72 ~ 68 F).

Since the temperature drop between closest and farthest outlet is about 1F, we can assume the temp just above the coil to be in 71 ~ 67 range. The inlet temp is in 86 ~ 82 range. The difference in average is about 15 F. Not very good at all.

However, there is one difference between testing condition and normal usage. Under normal usage, I will close the close outlet because it's almost right above the inlet. The cool air comes out and goes right back in the system. It's not a good design actually. I will measure the temp drop under that condition next time. But I would expect the difference to be small.


Originally posted by thomefan2579
also can you get a temp on the return near the furnace and one just above the a coil so we can get a temp drop if your 18-20 degrees its working pretty dang good

[cme4oil]

You have given a lot of information but I am a little confused with the results you stated after setting the thermostat at 75 and levaing it for 27? hours.

You said: I do understand the difference between efficiency and capacity. And neither of them hold up to my expectation. I set target temp to 75F and kept the system running for 27.5 hours (2:30PM to 5:00PM the next day). It took 10 hours to get to the target running continuously, while the outdoor temp has dropped from 91F to 76F. But it can not hold that temperature the following day starting from 10:00AM, it started running continuously again. The on/off cycles only happened between mid-night and 10:00AM. I think it's very inefficient, only marginally improved compared to my 25-yr old system.

My question is how high does the temperature go if you just let the system run? It's not really clear in your answer here.

[grandtiger]

The following day is 1 ~ 2 degree cooler on average and the cooling system can only maintain 76F when the outdoor temp is mostly at eighty something degree (hit 90 for 1~2 hour max).

The most problem here is that it ran non-stop. During on/off cycles, the indoor temp will hit 76 and system turned on, but it will cool back down to 75 and then system turned off.


Originally posted by cme4oil
You have given a lot of information but I am a little confused with the results you stated after setting the thermostat at 75 and levaing it for 27? hours.

You said: I do understand the difference between efficiency and capacity. And neither of them hold up to my expectation. I set target temp to 75F and kept the system running for 27.5 hours (2:30PM to 5:00PM the next day). It took 10 hours to get to the target running continuously, while the outdoor temp has dropped from 91F to 76F. But it can not hold that temperature the following day starting from 10:00AM, it started running continuously again. The on/off cycles only happened between mid-night and 10:00AM. I think it's very inefficient, only marginally improved compared to my 25-yr old system.

My question is how high does the temperature go if you just let the system run? It's not really clear in your answer here.

[thomefan2579]

tiger 15 is not great but not horrible i have not done a split on mine either try this set it at 75 and leave it there turn it on in the am and let it go let us know if it stays there or not maybe even try 70 i just check my temp from return to vent and it was 16 and my house stays at 70 no matter what temp it is outside but i let mine run 24/7 i would try that and see what happens if it can pull a house down to 70 and hold it in 90 heat your fine. my system runs alot as well highest bill last summer was 75 bucks and it was a hot summer here in ohio

[grandtiger]

Thanks for your advice, I have run the system on a not very hot day by setting target temp to 75F, it ran 19~20 hours on 24 hours basis, and it could not stay at 75F.

I think the most important thing is whether skipping those important steps during installation is acceptable, and what kind of short-run and long-run problems are typcially anticipated. And how do I go about to dispute the problem and have a solution for it.

In the worst case scenario, I would have to find another contractor to fix the problem. I suppose our professional members here can provide a lot of insights how to remedy the system.


Originally posted by thomefan2579
tiger 15 is not great but not horrible i have not done a split on mine either try this set it at 75 and leave it there turn it on in the am and let it go let us know if it stays there or not maybe even try 70 i just check my temp from return to vent and it was 16 and my house stays at 70 no matter what temp it is outside but i let mine run 24/7 i would try that and see what happens if it can pull a house down to 70 and hold it in 90 heat your fine. my system runs alot as well highest bill last summer was 75 bucks and it was a hot summer here in ohio

[beshvac]

There might be nothing wrong with it, have it looked at by a technician.

[AIR PRO]

Geeze, are you kidding? The thing will NEVER pull down to 75* if you keep opening the freaking windows and doors and shutting it down. Your Air conditioner is nothing but a big de-humidifier, it's going to pull the humidity out of the air before you notice a significant temp drop. How can it do it's job if you aren't letting it?
Temp drop across the evap coil will not tell you anything either if you measure it at high indoor ambient temp/humidity. You would think with a B.A. in HVACR you would know all this, I mean this is second month tech school theory we are talking about here.
A properly sized and installed system will run 100% of the time in full load conditions. Let the thing do what it is designed to do, and stop opening up the house and shutting it down!