Proper Cooling? How Do I Measure A/C Temp?

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Old 05-10-03, 10:53 AM
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Proper Cooling? How Do I Measure A/C Temp?

Unit: Trane Multi-Stage Heat Pump w/Emergency Heat

4 years old

House: Two story brick

Air vents are on the floor

Unit in Question is separate upstairs unit; the system/air exchange unit is upstairs in bonus room over garage; other rooms upstairs are 4 bedrooms and 2 baths (none of the rooms are very far from unit)

State: Central North Carolina; current temps in 80's/90's

When we had our home inspection done in October, the inspector said the upstairs air unit wasn't cooling right; the owner had an A/C company come out, and they wrote a letter saying there was nothing wrong, it was cooling properly/didn't need freon, etc.

Now that we've started using the A/C, I have to wonder if it is cooling properly. I have my A/C on 76 degrees, and it's been running for several hours, and the thermostat still says 80 (I know maybe the thermostat itself won't be what the cooling temp really is since the hallway is hotter than the rooms/no air vent in hallway); I put a thermometer (regular portable one to measure room temp) over the A/C vent, and the air coming out was only registering 79 degrees. How do you measure the proper cooling of an A/C unit? Is there a special thermometer to do this/do you stick it down the vent, or is what I did just as good?

If I have my A/C set on 76, should the air coming out of the vent also register 76?

It seems like the past few days we've been using the A/C it will run all day long and the thermostat will only go down 2 degres or so--and we have it on auto. It is upstairs, a separate unit. The hallway where the thermostat is located is a bit warm, but all the room vents are open and the doors are open. And the thermometer put in a room still is only saying the temp is 78-79 degrees, even after a few hours of A/C running.

I want to measure it properly before calling this company back the said there was nothing wrong and asking them how come it's still hot if it's running right. The two rooms facing the front of the house are still 80 degrees after 3 hours of A/C being on 76; vents are wide open




Thanks for your help


Also, how often do A/C units need to be replenished with freon from normal use?
 

Last edited by Marc31605; 05-10-03 at 11:16 AM.
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  #2  
Old 05-10-03, 02:21 PM
tammi ann
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AC units shuld never have to be topped up with gas, if they do it means there is a leak somewhere which is what you most likely have because you should be getting a 15-20 degree difference between the temperature in the house and the temperature of the air coming out of the registers.
Check your filters and replace if dirty but from the temperature of the air coming from your registers it sounds as if the outdoor unit is not running or it so low on gas its not even funny. Get a good recomendation for a decent heating and air company and have themn check it out.
 
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Old 05-10-03, 03:20 PM
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temp drop

what is the temp difference between the air entering the system (return) and exiting (supply) ? this will tell us a lot
 
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Old 05-10-03, 07:32 PM
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What exactly do you mean by the air entering and exiting the return?

Thanks

My rooms stayed 80 degrees all day--11 hours later the A/C finally went from 82 when started to 78
 
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Old 05-11-03, 07:21 AM
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the air

going into the return grilles would be inlet, generally room temp. the air temp exiting the supply grill has passed the cooling coil, and the temp difference between the 2 will give an indication of how well the system is operating.
 
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Old 05-11-03, 10:51 AM
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O.K. Will get back later with an answer. Thanks
 
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Old 05-16-03, 06:41 PM
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hvac4u,

I haven't forgotten about checking the return/outlet--the temps cooled down, and we haven't had to use the A/C for past 5 days, still cool through this weekend. Maybe next week when it warms up again I'll be able to get the answer.

Thanks for your help
 
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Old 06-14-03, 12:27 PM
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O.K., it's finally warmed up again and we're using the A/C.

The upstairs unit (separate from the downstairs unit) is a Trane heat pump w/emergency heat unit.

The intake vent on the ceiling is 79 degrees, room temp is the same; the air coming out of the floor vent is 70 degrees

Is that normal operating temps? I turned the unit on this morning around 10 a.m. when the temp on the thermostat was around 82 degrees; I have the thermostat set at 77 or 78 degrees; the unit has been running all morning without shutting off, and it's set on "auto" (5-1/2 hours now), and it's still running, with the thermostat saying it's only 79 to 80 degrees (the room temp is 79) and should it take 5-1/2 hours to get from 82 degrees to 79 degrees?


Another question: On the inside unit, where the thin copper tubing/pipe is hooked up leading into the unit itself, there is a bolt there holding it on; there is a small amount of hissing/condensation coming out of there, minor drip--is this normal there?

Thanks again for your help

EDITED TO ADD:

The upstairs unit is a Trane XE1100 model

Also, I checked the temp of the downstairs unit; it is set at 78 degrees, and is 78 in the room; the air coming out of the floor vents is 61 degrees (the air at the intake is 79 degrees); it is a combo gas heat/a/c unit (but not a heat pump)
 

Last edited by Marc31605; 06-14-03 at 12:50 PM.
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Old 06-15-03, 09:22 AM
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that is

an 18 degree split....sound ok, monitor that to see if it changes, unit could be undersized, and not able to handle the load.
 
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Old 06-15-03, 10:19 AM
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As I said, it's only a 9 degree split. Today, A/C on 6 hours and still no cool down, and not much air coming out of vents on floor;

Checked unit outside, something is leaking and ice has frozen up around the unit and pipe that comes out. What does that mean
 
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Old 06-15-03, 10:24 AM
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A/C

If everything is clean as you say call a tech if you see ice it sounds like your low on Freon ED
 
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Old 06-15-03, 10:46 AM
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Before we bought this house last year (October), the inspector said the A/C was not cooling right. The previous owner had someone come out, they wrote him a letter saying it was cooling fine, and the owner himself said the guy said it didn't even need freon.

Sounds like something fishy going on here. Would you call the same company back and make them fix for free, or take to small claims and have someone else do the work? I still have the letter
 
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Old 06-15-03, 10:53 AM
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A/C

Id call a different company for sure . Then go for small claims. So if there is a leak you can get it fixed now. Have them go over the whole unit for sure ED
 
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Old 06-15-03, 11:09 AM
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9 degree split?

ok, downstairs has proper split, i misunderstood i agree with ed, also call the inspector and get a copy of his report if you do not have one, see what the split was when he inspected. ice is an important clue...low air flow or low rewfrigerant
 
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Old 06-15-03, 05:30 PM
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Here's what the inspection report says:

1st floor-59 degrees supply, 74 degrees return

2nd floor-67 degrees supply, 76 degrees return/poor cooling on 2nd floor

When I measured yesterday, it came as 70 degrees from the floor vent, and 79 degrees from the ceiling vent that holds filter/also 79 degrees room temp



The only thing I have from the a/c repair person that apparently checked it was a letter saying it was cooling within manufacturing specs (bull sh** I say)--I am going to ask them tomorrow for a service order from their visit--hopefully they still have it since it was October, but we haven't used A/C til now--we trusted these apparent Air Conditioner Professionals that run an A/C repair business don't lie and know what they're doing. I highly doubt they did anything but check the inside temp with their thermostat--the previous owner of the house said they told him it didn't need freon either, but I think they're all blowing smoke up someone's butt--there is no way that if this unit was working properly in October when they checked it and not used since they checked it that it would be this way now.

I wonder if a few dollars didn't go under the table to get the letter written without any service call at all. The previous owner did all the repairs he was to do from the inspection through a "repair everything" company who called out the repair people--I wonder if anyone ever came out at all from the A/C company and it wasn't the middle man/repair everything company that is in bed with the people to charge the homeowner for the repairs, but have their contractors write fake letters for a few bucks.
 
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Old 06-15-03, 05:53 PM
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interesting

that the home inspector failed the cooling, yet the "independant contractor" passed it......i would ask the "independant contractor" how he considered 9 degree temp drop "within specs" as it was already established by the home inspector that this was the documented split. honestly you will probably get nowhere, and the best bet is to call this to the attention of their service manager, be reasonable, i believe he will be too. good luck, you are kind of over a barrel.....
 
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Old 06-15-03, 07:08 PM
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AC -----cost

From oct to now just a very small leak in the freon would have you low on gas so it would ice up on you. You said first floor was 74o in and 59o out thats only 15o drop then?? Like hvac4u said I think you or over a barrel. If you cant get the paper work. One other thing I find ,that when you lose the freon when the unit is off look on the low side first for a leak ED
 
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Old 06-16-03, 07:26 AM
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I called the company that said it was fine this morning--the owner says that guy hasn't worked for us for awhile, you can lose freon after we checked it, a 9 point split from your inspector isn't wrong, he probably checked it in heat mode, not a/c, you've used your a/c when you use your heat from the heat pump, basically we aren't doing anything, it's been 8 months.

He said we'll come out and make this right, but it will cost you for us to come to your door. I told him why would I pay you again when you guys couldn't do the job right the first time and I'm stuck footing a bill the previous owner should have paid for had you guys done the job right. I'm sure you can figure out a few choice words I have for this guy.
 
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Old 06-16-03, 09:45 AM
lynn comstock
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In your case, a Return air leak can cause poor performance. The machine can be fine.

Normal pressures, Low split:
Airflow is critical to evaluating any system. With a LOW split, I will assume that EXCESS air is not a problem and thus I suspect that duct leakage or poor duct insulation may be the problem. This is a commonly overlooked possibility. Here are some things you can check yourself:

1. Where were the air temperatures being taken? Measure the air entering and leaving the air handler right at the unit. This difference is the "temperature split". Use the same thermometer for all measurements. Then compare the air temperature entering the return air duct in the house at the hottest part of the day to the air temperature entering the air handler. A significant difference can be caused by outside or attic air being pulled into the duct and causing a heavy load on the system. Poor duct insulation may have the same effect.

2. Then compare the air temperature of the air entering the house through a supply grille to the air temperature of the air leaving the air handler. If the ducts are poorly insulated, the air entering the house will be significantly warmer.


I would invest in a 2nd opinion. The tech should get ALL of the following nine items of DATA and tell you his opinion of the problem and solution:

Outdoor ambient- condenser air entering temperature
Outdoor condenser air leaving temperature
Return air temperature- air temperature entering the indoor coil
Supply air temperature- air temperature leaving the indoor coil
The wet bulb temperature of the return air
Head (high side) pressure
Liquid line temperature (Small line at the outdoor unit)
Back (low side) pressure
Suction line temperature (Big line at the outdoor unit)

THE UNIT MUST BE IN CONTINUOUS OPERATION FOR 12 MINUTES AND THE DATA COLLECTED IN A FIVE MINUTE TIME SPAN. To get the wet bulb temperature, wrap a small piece of wet tissue around the sensor and hold in the return air stream for 90 seconds.

With that DATA, I can diagnose the proper or improper operation of your equipment and tell you what problem is or isn't.
 
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Old 06-16-03, 04:29 PM
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Tech came, he checked everything, it was 3-1/2 lbs low on freon. Cools great now. I think the previous owner and the a/c tech or repair middleman that hired him that checked it out previously are in bed together, or the previous a/c tech just didn't do his job right (the previous owner was not in town anymore, and the a/c tech probably collected his money and didn't do squat). So we are out $120 the previous owner should have paid.
 
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Old 06-17-03, 12:39 AM
lynn comstock
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Thanks for the feedback. I'm glad that the problem is identified.
 
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Old 06-17-03, 06:52 AM
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A/C

I hope you had this tech look for leaks at this time also. ED
 
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Old 06-17-03, 07:25 AM
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Yes, he looked for leaks and didn't find any. He's guessing the freon was never at full capacity when it was installed.
 
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Old 06-17-03, 07:30 PM
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Unhappy Gas and go...

Get ready to pay again...if its down 3.5 #, it will be loosing it's capacity within the next month...gradually doing less. Sometimes it is hard to locate leaks. Injecting a UV dye is the solution, because some leaks only escape under vibration or high heat or pressure, with dye in the system, an ultraviolet light will identify where it's leaking when it does. The house is protected against this type of stuff under law, and might even be covered by your insurance...call them, all they can do is say no.
 
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