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Old 06-29-2012, 05:19 PM   #1
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70 degree Supply Air


Hey all,

I have 77 degree air going in my return and 70 degree air coming out of my vents and the temp in my house keeps going up.

My thermostat is set on 72.
My house is 1200 Sq ft, 1 story.
I have a 2 ton TRANE XR11 unit with a 2 ton American standard air handler upstairs.
Both coils are clean.
My air filter is clean.
Air handler is on HI speed and blowing plenty of air.
I have had 3 techs out to check out my AC and they all say my freon is fine and that the only issue is my house doesn't have enough insulation. I'm calling BS.

My ducts are in my attic.
It's an extended step down plenum with Flex duct running to each vent.
My ducts are sealed... trust me ive been up there a million times checking.

I have one of those temp guns and when i check temp going into the return it's 77 degrees. Coming out of the supply it is 69-70 degrees.

I have the copper line outside well insulated. It is cool (67 degrees) and is condensating.
The small line is about 95 degrees though it's 93 outside so I dunno if thats right or not.

My attic is vented with 3 gable vents, 2 of which have fans on them blowing air out and I have a roof fan as well.

I believe its supposed to be a 20 degree drop from return to supply correct?

I have done quite a bit of research and work on this hence the plethora of information. Doc Holiday is probably tired of seeing me post and I am beyond frustrated with this stupid thing.

One of my friends told me that now that my AC is blowing more air my Freon charge needs to be adjusted. Is this true?

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Old 06-29-2012, 05:39 PM   #2
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70 degree Supply Air


Did any of the techs mention superheat or subcooling?

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Old 06-29-2012, 06:54 PM   #3
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70 degree Supply Air


Any chance we can talk you into buying a better test instrument? Temp guns are not accurate enough. A multimeter that comes with a K type thermocouple and that can check amps would be best.

The AC might be working right but one of the heat elements is coming on. Getting an accurate supply dry bulb and wet bulb temp along with the same for the return and verifying which speed the blower is on we can calculate how many BTU the AC is moving,after making sure none of the elements are on of course.
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Old 06-29-2012, 07:46 PM   #4
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70 degree Supply Air


Assuming the tech is correct and the freon level is right, and also assuming the compressor and coils are in good shape and your fan speed is correct. I was wondering if your picking up additional heat from the ductwork so that most of your cooling is being wasted in losses getting to where the cold air needs to be. I'm also guessing this system has worked fine in the past and it's not your first season with it. If it is, the AC may be undersized for the area to be cooled. Is the flex duct insulated good ? Moving more or less air will not be a factor to add more freon. AC units can only take so much freon that's why we do sub cooling and superheat measurements. Do not add more freon, if the charge is correct. If someone did add more freon they may have mix the wrong type and the system will never run right until the freon charge and type is what it's supposed to be. These are all guesses If I were to see it I could tell you right away what it was. Just my 2 cents....
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Old 06-29-2012, 07:46 PM   #5
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70 degree Supply Air


"Temp guns" are worthless for this purpose. Something like a $15 Weber digital grill thermometer works great. Stick it up inside the grille to measure air temperature, and give it a couple of minutes to get an accurate temp. The problem with I/R point and shoot thermometers are many. For one, they measure the temperature of a circular area whose diameter increases with distance. So if you stand on your floor and point it at a ceiling register, you're measuring the temperature of the register and the surround ceiling drywall, when you want to be measuring the air temperature. If you get closer, it will be more accurate, but you're still measuring the temperature of the register, not the air coming out of it. However, the longer you keep the thing in the cold air stream, the less accurate your results will be. I can make my Fluke read 10 F low for several minutes just by cooling it down. I once saw a tech hold his I/R thermometer under a cold air register for several minutes waiting for the temperature to drop after adjusting charge, and I was just silently facepalming the whole time. Speaking of air coming out of a register, the reason you stick a real thermometer up in the grille is to eliminate mixing with room air. Finally, temps measured at return and register can be very misleading due to heat gain if the ducts run through a hot attic. For example, you might read 13 F whereas the true drop across the coil is 20 F.
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Old 06-29-2012, 07:52 PM   #6
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70 degree Supply Air


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Originally Posted by tima2381 View Post
Finally, temps measured at return and register can be very misleading due to heat gain if the ducts run through a hot attic. For example, you might read 13 F whereas the true drop across the coil is 20 F.
By "misleading" I mean you might suspect your system isn't working right due to low freon or whatever, when the real problem is the heat gain in the ducts causing you to lose a lot of your cooling. If that's the case, you might be able to at least partly address the problem by wrapping the ducts with more insulation. For example, going from R4.2 to R6 might save you 2-4 F depending on length of the duct and attic temperature.
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Old 06-29-2012, 09:42 PM   #7
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70 degree Supply Air


standing out at the condenser you should have a 10F rise on air into the coils and then blowing in your face should be hotter then the day.....that suction line temp is telling us your short on freon should be ice cold like a beer can..forget about more air more freon babble have him add air to his tires if he wants to go faster...hi speed in cooling on the air handler is so you get as many passes on the air to pull the return heat and do that 20F split there.what did the 3 brainsurgeons write on the tickets after the servcie all is working splits pressure....what.are you getting any condensation water running out of the uit....
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Old 06-29-2012, 10:04 PM   #8
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70 degree Supply Air


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hi speed in cooling on the air handler is so you get as many passes on the air to pull the return heat and do that 20F split there.
Higher speed doesn't necessarily imply better performance. You need to consider the sufficiency of the return and ductwork plus determine the proper CFM/ton ratio to balance latent and sensible heat removal. My oversized system came set on High. It should have been Medium Low the whole time, two speeds lower, the next to lowest speed. The system never worked decently on High. It worked OK for a few years on Medium. It's working better still on Medium Low, which gives me about 375 CFM/ton and significantly better humidity removal. This is all with service to set the charge properly.
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Old 06-30-2012, 06:45 AM   #9
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70 degree Supply Air


Quote:
that suction line temp is telling us your short on freon should be ice cold like a beer can..
I would agree that perhaps the system is short on refrigerant, but I wouldn't trust the "beer can" measurement. I've seen plenty of systems working perfectly that didn't have that "beer can" effect.

Quote:
I have the copper line outside well insulated. It is cool (67 degrees) and is condensating.
The small line is about 95 degrees though it's 93 outside so I dunno if thats right or not
If this is an R22 system, and those are accurate measurements, then you've got some serious troubles. That suction line temp translates to a vapor pressure of ~115. If the "pressures" are right, according to the tech, and you're in the 75 psi range, then you've got superheat of 40+ degrees. If you're in the 250 psi range on the high side, then you've got about 70 deg of subcooling (which is way, way, way too much).

However, it's difficult to say this for certain unless you have accurate measurements with accurate instruments. The point-and-shoot guns are NOT accurate enough to measure refrigerant line temperatures - you need a Ktype or other accurate sensor to check those.

Ask friends and family for recommendations. When you call those companies, ask to speak to a technician, and ask that tech if they can measure superheat and subcooling. If you get that "uhhhh ... ummm sure I guess so" sort of answer, find someone else.

Good luck in your quest to find a true HVAC technician. They're becoming quite difficult to find!
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Old 06-30-2012, 12:58 PM   #10
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70 degree Supply Air


Doc no they never mentioned superheat or subcooling.

Marty, the blower is on high and according to the guy who helped me find the motor speed should be blowing 1200 CFM now. I'll see if i can find better test temp test equipment.

Kapriel they didn't just pump more freon in they used the gauges to make sure it was the correct level. This is my 2nd season with the AC unit. Last year was a struggle too but I thought it was due to the lack of air movement and speed. The air movement did help but not enough. All the flex duct is R6 and the 2 i replaced i replaced with R8 and the temp at those 2 vents is the same as the rest. Though I must say at night when the sun goes down the temp coming out of the vents drops down to about 60 or so.

tima I'll get a "real" thermometer rather than the temp gun haha. So much hate for temp guns on this forum! My trunk is R4.2 fiber board and the ducts are all R6 except 2 that are now R8. It does work better on high. When it was on lo it was literally just a trickle of air coming out.

Thanks biggles ... um only 1 of the techs was a tech that actually charged me. I work for the public works division of the navy so the other 2 have been ac tech friends that I work with. The air outside blowing into my face isn't hot at all. In fact yesterday when i was cutting the grass i went over there to get a refreshing breeze. That line definitely isn't ice cold. More like a beer that has been out of the cooler for a while and is sitting on a table in a puddle.

tima the humidity in my house is normally a constant 54 or so % despite being 80%+ outside so i think its removing enough humidity. Pipe outside drips like a champion!

scott I don't know what superheat and subcooling are... guess ill need to do some research on that one. It is an R22 system. Those temp measurements were done with a thermometer my ac tech friend had.

One of my Ac tech friends is coming out monday to check the freon levels again and see if its lost any to see if there is a leak or something.

I was definitely concerned about the air coming out of the outside unit not being hot... i remember from my parents house is was very hot.


Thanks for all the inputs guys i definitely appreciate it! I will definitely post the resolution if it ever happens
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Old 06-30-2012, 01:10 PM   #11
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70 degree Supply Air


full charge should be 10F above the temp around the condenser inlet air your missing freon....another trick is to block the air out wih a garbage can cover that LL should heat up as you slide over the air coming out,,,,, then the LL will drop in temp as you allow air to discharge...if it isn't the freon the valves on the compressor are worn when residential guy charge they always brab that suction line going into the condenser...as the gas is being sucked i the LL is filling on the actual condenser 4-5 rows and the LL to the furnace is sealed 100% liquid and the suction goes ice cold in a second...

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Old 06-30-2012, 05:26 PM   #12
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70 degree Supply Air


OK he will be here monday afternoon with gauges and gas so we can get it at the right levels I hope. Btw i took my wireless thermometer that normally sits in my window to see how hot is outside and i threw it up in the attic. It's 125 up there! No wonder my AC is strugglin. Time to get some more fans in that piece
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Old 06-30-2012, 06:19 PM   #13
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70 degree Supply Air


if you have a basement it being down there would make a big difference on the cycles.venting some of that 125F can only help with the supply/return ducting being surrounded by it.the air handler sucks air on that return from any place it is leaking coming back thru the attic imagine 125F attic ait mixing with your spaces 70F return..double check that collar onto the back of the air handler 360 degrees around same with the supply connection going out

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Old 07-01-2012, 05:07 AM   #14
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Those temp measurements were done with a thermometer my ac tech friend had.
Then you've definitely got some refrigerant side issues, most likely bad valves in the compressor.

As others have said, on a hot summer day the air coming off that condenser should be very warm. If it's not, you're not condensing that refrigerant, which means you're not cooling.
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Old 07-01-2012, 05:19 AM   #15
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70 degree Supply Air


Have the guy that checks it on Monday check the temp difference at the air handler. Register temp checks don't tell you if the A/C unit is working right.

Have them take SH and SC. They will also need to take the actual indoor humidity reading, and convert it to WB, or take a WB reading.

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