Originally Posted By: tpriddy This post was automatically imported from our archived forum.
In testing the A/C I currently use the thermal gun. I set the thermastat at 60 degrees wait 15 - 20 minutes for the pressure to build and take the difference, if 15- 20 its good if over or under recommend service. Is it better to be invasive and take the temps in the unit? Should I set the temp to something other than 60, is 15 - 20 difference according to texas SOP just says test for proper performance; such as observing the temperature difference. I just never feel like I’m not serving my client the best I can. This is how I was taught, just when I perform this part of the inspection I feel like I’m just not doing enough.
Originally Posted By: dedwards This post was automatically imported from our archived forum.
Do you look at the condition / cleanliness of the evap coil? condenser coil? The circulating fan? If the fan blades are filthy chances are very good the evap coil is too. When that gets clogged the CFM goes down and consequently so does efficiency. I get a reply from people all the time…“Its working, see you can feel the air coming out of the ceiling vents.” That just means the circulating fan is working. You could completely remove the AC or just go to Fan “ON” and that will work. Filters or lack of is another area overlooked. To have the evap coil professionally cleaned takes several (more like four) hours and it has to be literally removed and chemically boiled out with high strength coil cleaners. Then dried, system vacumned down again and tested to set the system up properly. Figure on about 350-450 dollars depending on where you live. People don’ like to buy a house only to find out they have to have the AC system serviced right after moving in. Did a house yesterday, fairly new nice house in a gated community, Heat pump working like a dog with a 2 degree split. Max cooling at the registers was 75 degrees F. Humidity in the house was at 76%! The reason was there was sheet of ice on the evap coil and the metering device. The ice would form, then melt and drip into the cavity below the AC unit. The only thing good I found was they had foamed the framing so none of the water was getting out into the carpet. They knew it was happening cause there were several pans and cups in the space to catch the water. Some HI would have missed this because they do not open up the access panels and look around. Takes all of a couple of minutes. I called the Realtor right then and let her know what was going on and they needed to get someone out there ASAP before they had a REAL mess (mold,etc) on their hands. The “M” word scares the crap out of them and they usually get on it right away. Recommend anyone that can take an HVAC course at night to do so. Worth every penny. Hope this helps.
Originally Posted By: tpriddy This post was automatically imported from our archived forum.
I test temps at return and closest supply register for a 15 - 20 diff. I figure if it is not between there that freon is low, outside and/or inside coils are dirty, or there is a dirty filter. I always check the filter and check to see if there is any water in the pan. I also check the outside unit to see that con line is insulated and that there is not excessive rust on the fan and/or compressor. I never open up the inside unit unless I can view the coils from the return plenum.
Originally Posted By: dandersen This post was automatically imported from our archived forum.
AC) is the biggest cause of <20 delta T here in TN. When it is 190 degrees in the attic (where the air handler is located) the heat gain into/through the duct will raise the measured temp well above the 20 degrees your looking for. There is nothing wrong with the unit, but there is something wrong with the attic ventilation (even though it “passed code”).
Originally Posted By: jonofrey This post was automatically imported from our archived forum.
dandersen wrote:
One you should keep in mind is the "Cold Beer Test".
Grab the suction refrigerant line. If you don't feel cool (heat < your hand temp) the unit is overloaded or undercharged. Ice should never appear on any part of a residential A/C unit.
This is the part of the job that gets me searching for the closest pub after the two o'clock inspection. 
Originally Posted By: bking This post was automatically imported from our archived forum.
I agree with the problem of using temperature differentials as a pure test. If you have good differential then the unit is producing but may have other problems that can be found by looking inside the unit.
If the differential is only around 10 degrees this can be normal in some circumstances such as, closed up house around 80 degrees with a unit that is undersized or barely adequate for the "home". The "home" includes many things such as the current OAT, insulation amounts, direct sunlight, quality of windows, number of windows, number of floors served, number of return ducts, size of return ducts, number of supply ducts, number of people in the house.
Write up these situations as appears to be cooling but may need further evaluation by the occupant under different conditions to determine if performance is acceptable.