A/C performance

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  #1  
Old 05-19-15, 06:48 AM
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A/C performance

I had a 1.5 ton system installed last year which never seemed to perform that well. Today I turned it on at 8:45 AM and set it to 60 and these were temps

8:45 AM
69.8 degrees inside
55% humidity inside
68 degrees outside

11:36 AM
68 degrees inside
52% humidity inside
73.2 degrees outside

2:53 PM
70 degrees inside
52% humidity
83 degrees outside

5:15 PM (house gets shaded out by 4 or so)
72 degrees inside
51% humidity
80.6 degrees outside

I know the fan is set to high, but there doesn't seem to be enough flow to maintain a temp. I removed the filter and flow didn't improve. I would say probably the in/out delta is 15 degrees. There just doesn't seem to be enough of it. This is in VT. It's a 900 sq ft house with walk in basement so 2 floors of cooling. The basement is naturally cool. What it seemed to be doing was exchanging the basement air with 1st floor air because at the end of the day, the basement was warmer that usual.

As I said it never really worked that well and the response from my first complaints early on was that it was working correctly for it's design temp.

I'm thinking it might be undersized a bit.

any ideas?

thanks
 
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  #2  
Old 05-19-15, 09:42 AM
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Get an exact delta T and let us know.
 
  #3  
Old 05-19-15, 09:57 AM
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One thing I like to do is take the house out of the equation first and I like to use a thermometer instead of guessing that it's about 15f delta. Wait for outside temps to be 80f or higher and have the system on and cooling for 5 or 10 minutes before starting. Get a accurate thermometer and put it right at the air intake stick it in a vent/register and measure the temperature of the air coming out. The air coming out of the vents should be 15-20f+ colder than the air going into the system. It sounds like yours is but I never like to rely on "seems like".

Whether or not it's properly sized for your house it a totally different issue. You can't tell just by square footage. You also need to consider how the house is constructed, windows, insulation... But I assume your 900 square feet is only for the upstairs and you imply that the system is also doing the basement area which doubles your square feet to 1'800. Personally I'd be wildly guessing for a system closer to 3 tons if that's how much space you're cooling.
 
  #4  
Old 05-19-15, 12:01 PM
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Ac performance

AC PERFORMANCE can be checked safely & easily by you.
Many valid performance tests have shown that air conditioning systems 'on the average' only deliver to the conditioned areas between 59 & 63% of their Nominal Rated Performance.

Easy Safe testing of your A/C or heat pump cooling performance for all the visitors to use:

First, make sure the return air filter is clean, and then you should get a digital probe thermometer that reads in tenths degrees, (though U can use any mercury thermometer) and a low cost percent relative 'humidity gauge 'to check the 'indoor' humidity level.

If you have an air conditioner that was manufactured between 1992 and 2005 it will 'probably be' a 10 or 12 SEER (though some were higher SEER even back then) R-22 refrigerant units.

When the temperature reaches around + 80 to 95F outdoors and the indoor temperature is 80F and the relative humidity indoors' is right around 50% RH the outdoor condenser temperature split should be around 20 to 21F above the outdoor temperature.

If the indoor temperature is 75 and the relative humidity is 50% then the air discharge temp-split off the condenser should be around 17F.

The indoor temperature split between the return-air at the supply air grille closest to the air handler should be a 19 to 21F temperature drop with either an 80F or 75F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

If the indoor temperature split is too high may have very low airflow which needs to be brought up to its normal CFM Rate.

If the outdoor condenser split is too high your air handler may be drawing hot outdoor air into the return from the attic causing the high condenser discharge air temperature; or it has dirty coils or lack of ambient airflow through the coils, check for cottonwood if trees are in the area.

On the new air-conditioning systems & any systems at 13 SEER or higher, the outdoor condenser split is lower than it is on the 10 to 12 SEER units; the indoor temp-split is the same.

New 13-SEER units have a condenser temp-rise 'at above conditions' of close to 17F; a 16 or 18-SEER usually around 9 or 10F need model numbers for more definitive numbers.

If the temps are within +/- a degree or two, that air-conditioner is performing fairly well; if not, call an HVAC service contractor (in your case the installing contractor) and show them your test results; tell them you want it to pass their Delivered Performance Test.

If they don't know how to perform those tests call to find someone in your area hopefully that can do those tests; with modern test instruments they are not that difficult to do.

Get others to help you do a 'free-online' whole house load-calc on your home; print instructions & follow them. HVAC Load Calculation - Manualj - Whole House Loadcalc
 
  #5  
Old 05-26-15, 09:22 AM
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thanks for the info. I've measured it before and air coming out was high 40's to low 50's and inside temp around 67. That was with high 80's outside.

But I just measured again and it's 66 coming out and 70 by the intake. So I'm guessing the system lost coolant.
 
  #6  
Old 05-30-15, 07:07 AM
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new problem

So the tech came out and put the gauges on it and it was low. Suspected a leak and rebraised a couple joints.

He started it up and it worked fine. Then the next day I tried to start it up. It ran for 1-2 minutes then the compressor kicked out (and fan stopped) and then the unit (both compressor and fan) started kicking on and off every few seconds. I turned off the call for cool and waited 5-10 minutes and tried again. The unit kicked on then off, then on and then stayed on and ran the entire day until I shut it off at night.

The next day, the same thing happened. It initially ran for a couple minutes then started to short cycle. But I wasn't able to get it to stay on.

The unit is a year old and has only been run ~10-15 times. I did add a soft start to it when it was first installed, but never had a problem with it starting. Started up fine before the tech came out, but it was low on coolant.

any ideas?

thx
 
  #7  
Old 05-30-15, 07:49 AM
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It sounds like it is low on refrigerant and short cycling on a low pressure switch.

If it is only a year old I would call the company back and ask for a different tech.
 
  #8  
Old 05-30-15, 07:54 AM
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Call the company that did the repair and ask them to send out someone to PROPERLY fix it. Do NOT scream at the receptionist or service manager or use any foul language but calmly explain the reason for the original call, what the technician did and what happened after he/she left. Do not try any DIY solutions but give the company the chance to make it right.

Please post back with the results.
 
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