A/C can't keep up during the day

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  #1  
Old 06-06-10, 12:48 PM
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A/C can't keep up during the day

Over the winter, I had a 95% furnace and new ductwork installed. My existing 2.5 ton A/C unit remained (although the contractors mistakenly removed it and tossed it in the back of their truck, until I pointed out the mistake.) I fired up the A/C for the first time yesterday, only to discover that it couldn't get the house below 80 degrees during the day. It did somewhat better at night. I had the contractor send someone out to investigate, and he did some refrigerant adjustments. It now blows cool at first (66-68), and then after maybe 30 minutes, starts blowing warmer. Any ideas what could be wrong? Thanks for any help you can offer.
 
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  #2  
Old 06-06-10, 06:08 PM
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4 questions for you. When it blow 66-68 air, what was the room temperature at that time? What is your Tstat set temp?
WHen it starts blow warm air, is the outside fan running? is the outside compressor running ?
 
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Old 06-06-10, 07:39 PM
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When it blow 66-68 air, what was the room temperature at that time?
Around 80-81
What is your Tstat set temp?
78
WHen it starts blow warm air, is the outside fan running? is the outside compressor running ?
Both are running fine.
 
  #4  
Old 06-06-10, 09:25 PM
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A 13 degrees (81-68) split is not enough, something is not right.you need at least 16, prefer 17 or 18. If your refrigerant level is correct, then the only other thing changed is your duct work. but before blame on the new duct, try to do this first:
If you have an AC guage and know how to use it, go ahead, if not, go to outside unit, while it is running, hand feel the pipes, the large one should be real cold and sweety, small one should be a little warm to touch. Please understand, since they removed the unit which open the system, there are lots of things can go wrong if they did not put it back right. Did they check the vacuum ? did they do a leak test ? you may need a new dryer....
 

Last edited by clocert; 06-06-10 at 09:48 PM.
  #5  
Old 06-06-10, 10:30 PM
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Make sure that the A/C blower speed was set correctly.

Did the contractor pull and vacuum? (charge could also be off)
 
  #6  
Old 06-07-10, 05:43 AM
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I would say you are low due to a leak some where.

As other said, did they do a leak test before charging the system?
 
  #7  
Old 06-07-10, 06:42 AM
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I don't know if they performed any leak tests, honestly. I'm going to get back in touch with them today for a follow-up. I'm wondering if they might have damaged something when they removed the unit and put it back. I guess it will wind up being my word against theirs, because they can make it look like anything they want.
 
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Old 06-07-10, 06:47 AM
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Thanks, Clocert. I think it's safe to rule out the ducts - they're working fine with the heating system, and they start out fine with the A/C, as well. I'm guessing it's either the compressor, or maybe some setting on the new furnace. That's nothing more than a guess, though, since I know nothing about A/C!
 
  #9  
Old 06-07-10, 10:49 AM
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NO, I don't think it is your compressor or new furnace caused problem. Call them back to check the A/C system, once they put the gauges on, they should be able to figure it out easily.
 
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Old 06-07-10, 04:13 PM
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They should never have removed your condenser from its refrigerant piping!

Doubt they followed all the steps toward a proper reinstall.

It could have air & moisture in the system... a leak & more...
 
  #11  
Old 06-09-10, 10:01 AM
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Update: the tech came out today and lowered the air flow by around 175 CFM on the furnace blower. He said that the compressor was shutting down. Thermometer in the register today showed 53 degrees, with return at 70 and inside temp at 73. Of course, it's cloudy and 76 out today, so it isn't a fair comparison to the blazing 93 degree day when he was here last. I'll have to re-test it when we get another hot day later in the week, to see if the air flow change did the trick. How's this sound to you experts out there?
 
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Old 06-09-10, 10:11 AM
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Should never have removed your condenser from its refrigerant piping

They should never have removed your condenser from its refrigerant piping!

Doubt they followed all the steps toward a proper reinstall.

It could have air & moisture in the system... a leak & more...
 
  #13  
Old 06-09-10, 10:28 AM
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A leak is not likely, since the tech said that it actually was over-filled (it was removed/replaced in the dead of winter). I don't think there's any way to prove that any damage was done when they removed the unit. It's about 8 or 9 years old - could be just a coincidence, or they could have broken it. I may never know.
 
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Old 06-09-10, 08:30 PM
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Did you call the dealer back since it not cooling anymore?
 
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Old 06-10-10, 05:20 AM
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Yes - posted this above. We're in a cool spell currently, so I'm still waiting for a hot day to re-test the system under a good load.

Originally Posted by flukeslapper View Post
Update: the tech came out today and lowered the air flow by around 175 CFM on the furnace blower. He said that the compressor was shutting down. Thermometer in the register today showed 53 degrees, with return at 70 and inside temp at 73. Of course, it's cloudy and 76 out today, so it isn't a fair comparison to the blazing 93 degree day when he was here last. I'll have to re-test it when we get another hot day later in the week, to see if the air flow change did the trick. How's this sound to you experts out there?
 
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Old 06-10-10, 08:24 AM
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With 17 degree split, that sounds OK, but I am not sure by just lower the fan speed will help that much at end. plus, I thought fan speed is alway more then 1000 cfm. (may be they measure it in a different way. may be by ton, but that is still small) Anyway, is the air blow at the register strong ? same as last year ??
 
  #17  
Old 06-10-10, 09:04 AM
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The flow from the registers doesn't seem any different so far. The real test will be when the sun is baking outside. If the compressor is going, is it worth fixing on a unit that's around 9 years old? The technician of course doesn't think that they did any damage to the unit when it was removed.
 
  #18  
Old 06-10-10, 10:09 AM
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Originally Posted by clocert View Post
I thought fan speed is alway more then 1000 cfm. (may be they measure it in a different way. may be by ton, but that is still small)
Newer system with variable speed blower has dipswitch setting to match system tonnage.

Rule of thumb is 400 cfm in most area. Some will have 350 for humid area and 450 for dry area.

So, for this poster system, air flow may be set at 1,000 cfm. My system is 2 ton, so my blows 800.
 
  #19  
Old 06-10-10, 11:39 AM
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Doubtful that they followed those "Best Practices...

Originally Posted by flukeslapper View Post
The flow from the registers doesn't seem any different so far. The real test will be when the sun is baking outside. If the compressor is going, is it worth fixing on a unit that's around 9 years old? The technician of course doesn't think that they did any damage to the unit when it was removed.
There are many procedures that have to be performed in the correct sequence to avoid problems after a system is opened up.

It is doubtful that they followed those "Best Practices."

Click to contact me & I'll explain...
 
  #20  
Old 06-10-10, 05:43 PM
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proper maintenance procedures

anytime the piping is cut the drier MUST be replaced. This is the only line of defence for the protection of the refrigerant system and it's components. If this wasn't done, be prepared for a new AC in the near future. Think of how you handle things your prepared to junk at the dump.....open piping??? wow!...
OH...When you take those temperatures don't try that at the registars...this must be done in the air stream just after the refrigerant coil and the return air entering the airhandler cabinet. You should see 17-21F. 175CFM won't shut down a compressor, an overcharged AC drawing excessive amperage will. One rule all hvac tech know is you don't charge AC systems in the winter without a return trip during warmer weather. When charging in winter it MUST be a weighed in charge. Performance curves are an alternative on cool days...but they are ballpark charges IMO
 
  #21  
Old 06-10-10, 06:42 PM
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a number of sequenced procedures that must be performed...

There are a number of sequenced procedures that must be performed in the proper order, - or there is apt to be problems down the road.

If You contact me I'll provide you with the important list.
 
  #22  
Old 06-11-10, 05:05 AM
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Thanks a lot for your great comments, guys. Let me see if I can respond to a few them. First, everything was replaced over the winter EXCEPT the outside A/C unit: furnace, A-coil, etc. The A/C is a 2.5 ton Bryant, about 8-9 years old. Jay11J: The new furnace is a Trane 95% 80K BTU, but is doesn't have a variable-speed blower. He switched a couple wires on the unit to slow the blower down.

hvac01453: not sure what you meant by "the airstream, just after the refrigerant coil" vs. the register for the temperature check. He was testing at a register about 8 feet from the furnace, and at the return grill, which is around 16 feet from the unit. I was thinking the same thing about the A/C unit being removed recklessly. There's no visible evidence of any external damage to it - seems like they may have been gentle with it. Of course, that doesn't mean that something wasn't damaged internally - there's no way I know of to prove it either way.

HVAC Retired: Since I didn't watch them reinstall the unit, I wouldn't know if they followed the sequenced procedures that you referred to.

We're getting some hotter weather this weekend, so I'll be able to see whether his modifications made a difference.
 
  #23  
Old 06-12-10, 02:20 PM
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Here's the latest update: With the temp outside at 90, and the inside temp at 78, I turned the A/C on. Register closest to unit was blowing at 60, with others at around 62. So far so good. The dryer was hot, IR read 99. After 15 minutes, the inside temp was down to 76, and the dryer was down to 91.

After the 15 minute test, I raised the thermostat to 80 for a few minutes, then took it back down to 72. When the system kicked on, there was no compressor buzz, and no cooling. Thoughts? Am I just out of luck?
 
  #24  
Old 06-12-10, 03:00 PM
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Your system must not have a time delay. It's hard on the system to start up right up after it just been shut down.. Most system has 5 minutes or so time delay to allow the system to balance out.
 
  #25  
Old 06-12-10, 03:08 PM
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Thanks, Jay. Looks like you were right about the delay. It took more than five minutes, but the compressor is now running again. I'll let the system run for a while to see if it goes warm on me again.
 
  #26  
Old 06-14-10, 05:38 AM
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sounds like your back in business

the concern I have is not how it may have got banged around, but rather if dirt or water may have gotten into the opened piping...did the drier get replaced? The temps on the drier are normal...PS IR guns are ballpark at best, I have one and only use it to shoot registars to see if cooling or heating is comming out of them, so that I don't have to use a ladder to get up to the ceiling registars is commercial businesses. The temp reading I refered to earlier are all taken at the furnace. Infiltration on a return may lead you to think a return is cooler than it really is, and a temp taken at a registar picks up heat cooling off the ducktwork and registars on the way to the room. To eliminate this you take the temps at the unit.
 
  #27  
Old 06-14-10, 10:31 AM
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At this point, I don't think Flukeslapper can do anything except hope his system is in good shape and runs years without any problem. Since he did not see the tech do all the work, so he does not know how the system was put back together, good or bad, he can not prove anything anyway. Now with 17 degrees split and strong airflow, the system may be OK, or at least for now. GOOD LUCK to you Flukes..
 

Last edited by clocert; 06-14-10 at 12:35 PM.
  #28  
Old 06-15-10, 07:08 AM
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Thanks, guys, for all the help and suggestions. So far, it seems like the system is behaving again. It's maintaining the cold output, which was the original issue. Hopefully, all is well.
 
  #29  
Old 06-25-10, 02:27 PM
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Here's an update on the ongoing A/C saga, and what may be a stupid question (if so, I apologize):
Today is sunny and in the mid 90's. I ran the following test, starting at 4:30 pm:
Outside temp: 93
Inside temp: 83
Set thermostat to 79
Registers blew cool air (IR read 64), and compressor seemed to be working properly.

After 30 minutes, the inside temp was only down to 82. It doesn't seem to want to go much cooler than that. Is there any way that you guys know of to determine whether it's a system problem, or if the house is just too much of an oven to cool down? Thanks again for your thoughts.
 
  #30  
Old 06-26-10, 02:39 AM
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The issues are (1)the temp of the conditioned air, could be low on freon which would indicate a leak requiring fixing. You might just feel the temp of the exhausted air from the condenser just for grins and cost nothing...should be very warm, bordering on hot. Also, is the big copper like going into the wall very cold and very wet? (2)the delivery of the conditioned air, which may be suspect. Are you getting a good strong flow from all registers? If not you could have duct leaks, dirty filter or indoor coil (3) environmental issues...system is undersized for issues like excessive direct sun window or wall exposure, inadequate attic insulation or ventilation, owners asking for cooler temps than system was speced for, hotter outside temps than designed for.
 
  #31  
Old 06-26-10, 07:22 PM
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Yep, I agree...

I would go into the attic and see if your attic fan is running.
It should be running when outside temp is in the 90's.
This is even more important when the duct work is in the attic.
 
  #32  
Old 06-26-10, 08:42 PM
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martymartin: yep, the attic exhaust fan is running pretty much all day lately, and well into the evening.

srercrcr: the system seems to be behaving properly, and all components except the condenser unit are brand new, including the ducts. I'm wondering if it's just the insufficient insulation in some of the house's walls. Had thermal windows installed, so they're not the culprit anymore.

Never had a place like this one before - it's a fighter.
 
  #33  
Old 06-28-10, 08:05 PM
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Smile The IR read out is very inaccurate

unless you are spending thousands for it. I would trust the face off your thermostat if its the removable type that will run without it... like a white Rogers or even the old one...Maybe you have one of those ones that are in the kitchen window for outdoor temps ... If the AC has 83F air entering the unit and the temperature output is 63F, and unable to drop the temp 1F in 1 HR the unit is too small. In other words the heat gain is equal to the heat rejected in the box, in your case the home... The unit is designed to reject heat to the tune of 17-21F. Your area is humid so its closer to 20F than 17. Arid areas use 17F.
I personally suspect, if you invest in a pocket probe style AC thermometer(looks like one that is stuck in a turkey) and you measure 6" before and after the air handler you'll find the temperatures much different from what you read before.
Also after reading the posts again, it appears that the airflow was slowed down to get the 20TD. Cooling is normally the high speed setting,... sounds like it got slowed to a med or med-high speed to get the desired result rather than finding the systemic problems, Tell em get back there and make it run like it did BEFORE he ripped it out... OH, quit playing with the stat. Set it and forget it!
The squeeky wheel gets the oil!
 
  #34  
Old 06-28-10, 08:25 PM
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hvac01453: Thanks for the info and advice. I have no choice but to play with the darned stat - if I leave it alone, the damn thing will run non-stop. I wish there was a sure way to be certain whether the unit is at fault, or the ducts are losing too much of the cooling, or the house is just a brick tent. I'll take your advice and get an accurate thermometer, but I'm pretty sure that the condenser is cranking out cold enough air. There's slight air leakage at the handler, and it's pretty cold. The bizarre thing is that right now, it's 82 outside, and I still can't get the house to drop below 82 inside. The house is just eating the cold air. I wouldn't believe it if I wasn't seeing it with my own eyes.
 
  #35  
Old 06-28-10, 08:37 PM
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Is the condensate drain draining lots of water?

When you step outside can you feel a difference? Do you have plenty of air flowing out of the regitars or is it just dribbling out. It should have plenty of force...Just for the hell of it, shut off the gas line to the furnace and see if it improves...a 2.5 ton unit should easily do a 12-1,500 sq ft home.
 
  #36  
Old 06-28-10, 08:54 PM
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Outside feels more humid, but not much warmer. The registers are pushing air reasonably well - not what I'd call forcefully, but cool air is coming out. I found an old thermometer (not sure how accurate it might be), and the air temp above the handler is 60, intake below by the filter is 74.
 
  #37  
Old 06-30-10, 05:21 AM
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Arrow This has the appearance of a poor install & setup...

Originally Posted by flukeslapper View Post
"The house is just eating the cold air. I wouldn't believe it if I wasn't seeing it with my own eyes."

Outside feels more humid, but not much warmer. The registers are pushing air reasonably well - not what I'd call forcefully, but cool air is coming out. I found an old thermometer (not sure how accurate it might be), and the air temp above the handler is 60, intake below by the filter is 74.
A 14-F temp-drop is only acceptable if there is a very high humidity latent-load in your home.

This has the appearance of a poor install & setup.

Also, before doing further diagnostics, both duct static pressures & actual airflow should be checked with an anemometer & CFM results compared, using the air handler's blower curve chart or graph for ESP - static pressures.

Do some Internet Google searches for - EER SEER Airflow
Also, search - superheat & subcooling troubleshooting

Though "Hotfrog" is full of hot air, some don't provide good information!
 
  #38  
Old 07-03-10, 04:52 AM
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charge

your likely low on refrigerant (leak) or it was never charged enough...there are several things it could be BUT you need a pro to remedy thisa one I feel.
 
  #39  
Old 07-03-10, 06:37 AM
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It doesn't seem like there's a leak in the system, because the lines get appropriately warm and cold, and the registers are blowing cool air. We had an 80 degree day the other day, and I let it run for a while, just to see how low it would go. Only got down to 75. It's supposed to hit 98 here tomorrow, so that ought to be interesting. I don't know if this situation will ever get resolved, but thanks for all of your helpful posts.
 
  #40  
Old 07-08-10, 07:01 PM
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pressures

what is the high side pressure and low side pressure. Suction line temp, liquid line temp?
 
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