A/C sending us to the poorhouse......


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Old 07-07-09, 08:04 PM
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Angry A/C sending us to the poorhouse......

Our A/C is cooling our apartment down to a comfortable level of 72, however it is running 22 out of 24 hours to do so. When the outside temp rises into the 90s the best it can do is 76-77 on the cooler side of the apartment, 79-81 in the livingroom with the big windows.
The apartment is ~1400 sq ft
New apartment so Insulation is good
Commercial Grade Window 10 x 6 on sunny side.
3 Commercial Glass Doors (1/8" Glass) on Sunny Side
All sunny side windows are tinted with reflective tint.
Commercial Grade Window 10 x 6 on full shade side.
2 other sides A/C apartment.
Corrugated Steel Roof with foam under rubber roofing.
The A/C is Carrier 2.5 ton.
This problem has existed since we moved in 3 yrs ago the apartment is only 4 years old. At that time the compressor was replaced under warranty because it was not working at all. More recently the evaporator was replaced due to a small leak.
Here are some temp readings I took using Infrared on a evening with moderate outdoor temps. I don't have access to the roof so I can't take readings from the condensor. If you need some special reading I can get the apartment tech to get them for you.
Evaporator Inlet/Room Temp = 71.1
Evaporator Core = 53 average
Small Pipe Exiting Blower = 69.5
Large Pipe Exiting Blower = 61
Nearby Vent = 54
Current Outside Temp = 78 (10:40 Evening)
No matter what temp I set it at it never seems capable of making the 1 degree swing (It is set that way because it never stops running with 2 or 3 degree swing).
The thing that stands out to me the most is that there is almost no condensation on the evaporator. We are in Florida with humidity of 85-99 yet there is not enough to even drain out of the pan. All other A/C's that I have had sound like waterfalls at this time of the year.
I recently spoke with neighbor with the exact same apartment and exposure that I have. He states that his apartment has no problem obtaining 72. My large windows are tinted and his are not!
Another note: When the evaporator was replaced the tech moved some sort of pressure sensitive valve with small pipes over from the old evaporator. Could that be the problem?
I promised the apartment A/C tech that I would do some research for him because he is stumped.
Thanks in adance, Mark
 
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Old 07-07-09, 08:54 PM
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It's best to always go back to basics. Ask the tech what the superheat and subcooling numbers are. Put away the infrared, you can't measure air temperature with it. use a thermometer.
 
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Old 07-08-09, 02:10 AM
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In S Texas we call for about 1 ton for every 500 sf to achieve around 76 degrees. Based on that, you would need 3 tons for 76 degrees.
To achieve 72 degrees you need even more. Why in the world do you need 72? I just read in some A/C material the lowest to highest comfortable temp for humans is 73-78 degrees. I use 78 and ceiling fans during the day. At night we use 74. When my wife interjects with a 73, I have to bundle up like it's Winter.
 
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Old 07-08-09, 05:53 AM
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72F is cold my friend you will run all the time, But your system should get you to 74F on the none big window side of the apartment on the 90F day.
Go to publix, buy one of those digital temp probs,
Stick it in the duct right above the air handler and then get a temp by your return air by your filter. You should get around 18 degree difference. If so the system itself is doing what it can.
 
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Old 07-08-09, 08:08 AM
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daddyjohn
I'm going to get the tech take some readings for me. He has stated in the past that all the temps and pressures are within tolerences.
srercrcr
The size was always one of my concerns but others with identical apartments don't have this problem. I was also concern about the 72 temp we set at until I ran into the neighbor who runs his at 72 without any issues. We run at 72 because if we don't it will be in the 80's in the sunny room if we start the afternoon at 75. Also it doesn't feel like 72 antway. I think that might be something to do with the fact that it is not removing any humidity.
There is a possibilty that the wrong unit was hooked to my apartment. The apartment next to me is smaller but has a 3 ton unit. Anothert A/C tech stated that it might need the additional size because it is a corner apartment. The blower/evaporater does match what is on the roof.
ClassicDave
I had 6 radio temp sensors one on the inside of evaporator one on the air intake of the evaporator, one in the attic and one in a vent close to the blower, one outside, and one in the livingroom and one of the bedrooms. I recorded all the temps for several months but they all seemed within reason.
 
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Old 07-14-09, 01:36 PM
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Here are the readings from the AC tech...

Suction 74/75
Liquid 232
Liq Temp 98.1
Subcool 12deg
Carrier with TXV Model 38YCC030340
Thanks for your input.
Mark
 
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Old 07-14-09, 02:00 PM
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Our thermostat here on the FL west coast is set at 82; ours would have to run 24/7 to maintain 72. I can't imagine what my electric bill would look like. The current FP&L radio ad running recommends 78. Beer 4U2
 
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Old 07-14-09, 02:59 PM
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Originally Posted by mark411
Suction 74/75
Liquid 232
Liq Temp 98.1
Subcool 12deg
Carrier with TXV Model 38YCC030340
Thanks for your input.
Mark
I get 14-F subcooling, which maybe too high.

Subcooling can be meaningless if airflow is way to low, or air is by-passing the evaporator coil. Make sure it is delivering around a 1000-CFM airflow that is actually going through the evaporator coil!

It appears that the refrigerant system 'could be' way over charged.

Also, the change-out evaporator or metering device may not be a match or TXV's Superheat setting is not set low enough to get the coil below the dew point.


You always need to check the suction line Superheat & the actual condenser discharge air temp compared to the outdoor temp & the temp the pres/temp gauge reads.

With a light indoor & outdoor load, you said the large pipe (suction line back to the compressor) was 61-F that might indicate that the TXV is not feeding enough liquid to the evaporator resulting in too much superheat & a not cold enough coil.

If there is NOT adequate airflow through the evaporator coil the TXV will not function properly. Look for air bypassing the E-Coil.

The head pressure would indicate an overcharged system with a very low heatload through the evaporator coil.
 
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Old 07-15-09, 09:13 PM
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HVAC RETIRED, thanks for the reply. I have a few questions..
I get 14-F subcooling, which maybe too high.
Are you calculating this number from what I provided somehow? I will pass the info to tech.

It appears that the refrigerant system 'could be' way over charged.
I will let tech know.

Subcooling can be meaningless if airflow is way to low, or air is by-passing the evaporator coil. Make sure it is delivering around a 1000-CFM airflow that is actually going through the evaporator coil!
The unit is about 4 years old and the inside seems undisturbed (Even after coil replacement). I don't see any gaps or open areas. What/Where should I look for as far as air leaks go.

Also, the change-out evaporator or metering device may not be a match or TXV's Superheat setting is not set low enough to get the coil below the dew point.
He moved the old TXV over when the evap was replaced. The new evap had a few more pipes running through it. There is a temp sensor buld/cannister strapped to the return line just inside the air handler. To test out the TXV should I make the sensor warmer or colder?

With a light indoor & outdoor load, you said the large pipe (suction line back to the compressor) was 61-F that might indicate that the TXV is not feeding enough liquid to the evaporator resulting in too much superheat & a not cold enough coil.
Will the suction line temp go up or down when function is improved?

Thx,
Mark
 
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Old 07-16-09, 05:00 AM
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Originally Posted by the_tow_guy
Our thermostat here on the FL west coast is set at 82; ours would have to run 24/7 to maintain 72. I can't imagine what my electric bill would look like. The current FP&L radio ad running recommends 78. Beer 4U2
83 here during the day 84 at night

72 ? brrrrr

break out the jackets and quilts



<input id="gwProxy" type="hidden"><input onclick="jsCall();" id="jsProxy" type="hidden">
 
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Old 07-18-09, 05:56 PM
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72 does not feel like 72

72 does not feel like 72 when AC is not removing the humidity. I am happy with 76 when things are working correctly.
 
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Old 07-18-09, 05:59 PM
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Refrigerant Guage Question...

Are these guages worth the money?
Digi-Cool | Digi-Cool
If I can get my AC working properly they will pay for themselves in 3 months.
Plus when I buy a house I can check my own AC from time to time.
 
  #13  
Old 07-18-09, 06:40 PM
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I didn't know you have a EPA license. If you don't, don't get caught. Minimum fine is $10,000.
 
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Old 07-18-09, 06:50 PM
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Not that I'm scarred of the JA's at the EPA, I'm not planning on charging/working on the AC, just diagnosing the problem. We spend so much money on AC herein Florida everybody should have a set of these guages. I heard there are AC systems with "Guages" built in now.
I guess I should mention that my power bill runs between $350 to $500 in the summer months for my 1400 sqft apt. My sister has a 5k sqft house with a well pump and a pool pump and her bill is only $300 to $400.
The FPL guy came by and we did all sorts of tests. Everything pointed to AC runtime. According to the hour meter on the thermostat it is running 20 out of 24 hours a day. I'll still swear they have the street lights hooked to my meter!
 

Last edited by mark411; 07-18-09 at 07:25 PM.
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Old 07-18-09, 08:05 PM
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An EPA license is required to attach gauges. Is the air handler in the attic? Has anyone tried to see if hot air is being sucked in on the return air side?
 
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Old 07-19-09, 06:17 PM
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Air Handler

The air handler is in a closet. The return air travels up through the attic then down into the closet. Opening the door to the closet completely eliminates the trip the air takes through the attic.
I have checked the difference between the intake air temp with the door open and closed. With the door closed there is a 2-3 degree higher temp at the return. Keeping the door open all the time only helps a little.
The ceiling is completely sealed so the only way to check for duct leaks would be to cut through drywall.
Is there a way to check for leaks without access to the ductworks?
 
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Old 07-19-09, 08:08 PM
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So there is no attic access? rats The return air travels thru a duct in the attic then dumps into the closet? Is that correct?
 
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Old 07-19-09, 09:13 PM
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So there is no attic access? rats The return air travels thru a duct in the attic then dumps into the closet? Is that correct?
Yes. It is a commercial style building that is built out into an apartment with 12 ft cielings. I cut through the drywall in one section and the view of the ducts was completely blocked by huge steel beams.
I'm not sure why the air goes back up through the attic. It seems like they wanted to centrally locate the thermostat but the air handler is all the way on one side of the apartment. The way it's setup, the air is sucked back to the thermostat.
 
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Old 07-24-09, 07:46 PM
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HVAC RETIRED, thanks for the reply. I have a few questions..

Subcooling can be meaningless if airflow is way to low, or air is by-passing the evaporator coil. Make sure it is delivering around a 1000-CFM airflow that is actually going through the evaporator coil!
The unit is about 4 years old and the inside seems undisturbed (Even after coil replacement). I don't see any gaps or open areas. What/Where should I look for as far as air leaks go. Could a dragging fan motor be the cause? I smell some sort of burning/ozone coming from the vents. It is very faint.

Also, the change-out evaporator or metering device may not be a match or TXV's Superheat setting is not set low enough to get the coil below the dew point.
He moved the old TXV over when the evap was replaced. The new evap had a few more pipes running through it. There is a temp sensor buld/cannister strapped to the return line just inside the air handler. To test out the TXV should I make the sensor warmer or colder?


Will the suction line temp go up or down when function is improved?

Thx,
Mark
 
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Old 08-11-09, 02:11 PM
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What are the chances that the TXV is the problem?
 
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Old 08-12-09, 02:19 AM
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I'll add what I can and ask a question.

What's your indoor humidity?

I'm in Florida also, and there is a steady _stream_ of water from my AC whenever it's running. If you aren't even getting a drip, I think something is wrong.

As for your indoor temp, I keep my place (2400 sq ft) at 72 as well, bill averages $280 (on a 4t heat pump), with no shade. Humidity is ~ 34%

If I read your post correctly, the air coming from your vents is 54. It sounds like you've got an issue with humidity removal, and it's also possible that a good portion of your cooled air is going somewhere other than inside the apt, maybe into the attic from a broken duct? Was the ductwork checked at all when the a/c tech came over, or did he just look at the unit?

When the air is put somewhere other than inside, that air then has to be replaced some how, by drawing it from any crack it can find with the hot, humid outside air. Next time the unit is on, crack a window (not on the windward side) and feel for a draft. If you feel air coming in, you've got a duct leak somewhere.
 
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Old 08-27-09, 02:38 PM
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Intake Temp, Coil Output Temp and Humidity

Please checkout this website which logs/graphs the tempature and humidity going into the air filter and the temperature of the air coming out of the evaporator.
It also has a sound and airflow sensor that are not accurate but do show when the unit is running(noisy and windy) or off (quiet and calm).

http://myairhandler.neatostreeto.com

User= actech pw= supertech
 
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Old 09-01-09, 06:34 PM
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Pendragon gave an excellent reply!

You don't have to have a service manifold to check your A/C's performance.

Here is a "Simple Easy Safe Way" to Check A/C's refrigerant charge & Performance without using a service manifold:
Record the outdoor temperature, then "Take a thermometer & check the air temperature coming off the outdoor condenser."

Depending on the units SEER Rating, the temp-rise for a 12-SEER condenser should be between 17 to 21-F.

Locate the small uninsulated copper line where it makes a bend, outdoors or indoors, so you can put a digital thermometer flat on it & insulate the TH with something (piece of the tubing insulation) read the temperature & subtract it from the outdoor condenser discharge air temp.

E.g., condenser temp 110, line temp 100-F that is 10-F subcooling & 8 to 12-F is usually a normally charged system. If it's considerably less than 10-F it could be low on refrigerant or need a Tech to check it; too far above 12-F it's overcharged, call a Tech, could also be a restriction in the lines.

You should own a low cost digital pocket thermometer & a percent of Relative Humidity gauge for checking the indoor humidity level.

We need two wet-bulb temperatures, & the indoor CFM airflow.
With that data we can ballpark the operating BTUH.- HVAC RETIRED
 
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Old 09-02-09, 04:34 PM
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HAVC RETIRED, based on your method of finding the SUBCOOLs, Can I assume the SUPERHEAT wil be equal to, subtract Inside air vent temperature from outside large pipe temperature? Another word, if the nearest air vent temp is 55 degree, the outside large pipe temperature is 66, then the SUPERHEAT will be 66-55=11. Is this correct ?
 
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Old 09-16-09, 09:58 AM
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It would be a very rough Ballpark SH

Originally Posted by clocert
HAVC RETIRED, based on your method of finding the SUBCOOLs, Can I assume the SUPERHEAT will be equal to, subtract Inside air vent temperature from outside large pipe temperature? Another word, if the nearest air vent temp is 55 degree, the outside large pipe temperature is 66, then the SUPERHEAT will be 66-55=11. Is this correct ?
NO, it is not correct.
A 55-F SST would require above 90-psig gauge pressure, not likely depending on the evaporator heatload.


Using "Goodman Expanded Performance Data," only at these data: 75-IDB & 63-IWB or 50% relative humidity; airflow 400-CFM Per-Ton, you would probably need to subtract 10 to 11-F from the supply-air temp to get close the the Suction Saturated Temperature (SST) as read on a manifold gauge.

Therefore, 55 - 10= 45-F | 66-F - 45-F= around 21-F or 22-F Superheat. This would be a rough Ballpark SH estimate.

I have not researched the above method, because we use the suction pressure/temp reading to get the SST.
 

Last edited by HVAC RETIRED; 09-16-09 at 10:04 AM. Reason: A 55-F SST would require above 90-psig
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Old 09-16-09, 08:12 PM
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HAVC RETIRED, I see the point, Thanks.
 
 

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