I saw it I read it and I still like my way of doing it I can not and will not change .
I think many are well above the SOP .
I am just a simple Great Home Inspector.
… Cookie
Nice David, excellent points to consider.
David,
While I certainly appreciate your expertize in this matter, I freely admit that HVAC is still my weakest subject. So please forgive my over-simplification, as I’m sure the entire process is much more complex.
In my (relatively dry) climate, air, when it passes over an “exchange,” will change in temperature. As Roy stated, there is a level of change considered to be within acceptable limits, based on a “generalist” inspection.
Until I have achieved a higher level of expertize in HVAC, I will follow the teachings of my predecessors.
I now see that this has been hashed and debated for quite some time in a thread that I did not participate in. I’ll let you and the others continue the debate, while I sit in and observe.
Jeff this went back even further, back into Jerry Peck days I had a dog fight with him once over this very topic. Its like bringing a knife to a gun fight it does not work.
I seem to remember that one too. Apparently, I wasn’t paying much attention then either 
David,
Your points are well taken, and are certainly based on fact. However, while researching the subject, and trying to stress the importance of performing a non-invasive inspection, I have found that measurement the temperature split between the high and low pressure refrigerant lines at the compressor and evalorator coil (when doing both is possible) and looking for between 15 and 18 degrees is pretty universal, even amongst HVAC specialists. This method has proven to be pretty reliable for a very long time. We are not engineers, and have limited time with which to work with while performing the inspection.
Again, I have spoken to HVAC folks in several states, with varying climates. 15 to 18 degrees is a good measure.
David,
Your points are well taken, and are certainly based on fact. However, while researching the subject, and trying to stress the importance of performing a non-invasive inspection, I have found that measurement the temperature split between the high and low pressure refrigerant lines at the compressor, and looking for between 15 and 18 degrees is pretty universal, even amongst HVAC specialists. This method has proven to be pretty reliable for a very long time. We are not engineers, and have limited time with which to work with while performing the inspection.
Again, I have spoken to HVAC folks in several states, with varying climates. 15 to 18 degrees is a good measure.
Here’s a simple explanation:
The most relevant test of Delta T is conducted at the refrigerant lines. Here’s why:
This Delta-T measurement is the difference between the refrigerant temperature entering and leaving the ***outdoor ***A/C condensing unit. The volume of air crossing the evaporator coil results in a increase of heat in the refrigerant return line to the compressor unit. When the refrigerant expands at the evaporator, it becomes super-cool (just above freezing). As the air passes through the evaporator, heat is removed from the air, and transferrs to the coolant, warming it clightly. Though actually warmer, the refrigerant return line is still quite cold (50-55 degrees F)This differential in temperature between the warm refrigerant supply line, and the cooler return line is the Delta-T.
The split in temperature across the coil should be around 15° to 20°, measured at the compressor/ condenser unit.
This is a good diagnostic check because it measures the latent heat of condensation as well as the sensible heat absorbed by the vaporizing refrigerant in the indoor evaporator coil. In other words, it helps to determine if the system is charged and cooling properly.
Barring any other variable, such as overcharging, undercharging, dirty condensor coils, defective blowers, defective ducts, or dirty evaporator coil, this measurement is pretty indicative of a properly coolling system.
Joe,
I’ve been writing reports all night! Your post just made me cross eyed! 
I will look at this more closely after some sleep!
At this point I agree with you measuring the line-set.
The reason I agree (besides what you stated), is because refrigerant temperature is relative to it’s pressure. It is a sensible heat measurement.
If we dig back in the “dead sea posts” I offered a solution of testing the HVAC by just touching the line-sets. This seems to go right along with what you posted. It is a heck of a lot more accurate than measuring air temps.
You can “feel” the capacity of the refrigerant by just touching the line!
For those who have taken the Building Science & IR course, you know that we can feel temp changes as little as 0.001C when an IR camera only detect 0.2 - 0.05C
I have tried to make this simple for all to be able to do. Some just want to take chances.
And how many of us speed on the highway and not get a ticket?
My simple version on this topic.
I take temp readings at the return and the FIRST duct into the home after the air handler, and the most distant register.
I look at the supply and first register to see if the system is cooling air and in a measurable way, I use the 14-22 deg guideline. If the system isn’t COOLING in these parameters then a HVAC service is recommended. If it is in parameters then I state that. (It shows I checked the system also)
The most distant register is to see how well the ducting is insulated and how well the system moves air, temperature is taken and a dollar test is done (If it blows my dollar around when held up…simple but it works). If the temperature is way off 5% or more at the end of the run it may indicate a insulation of duct issue, and eyes on in the attic or crawlspace usually confirms this. But this too is just a guideline to help me figure out whats going on with the HVAC system.
Using a thermal Laser gives you a a number that helps you make a judgment call…and thats what we get paid for.
Curt
Thanks Joe! I was hoping someone would come up with something else to consider.
I made a couple corrections where you obviously didn’t say what you meant. I just don’t want anybody to get off track. I hope you don’t mind.
Even under these adverse conditions your Delta T will go outside of the parameters!
The best thing about this procedure is that you are taking sensible temperature measurements with sensible heat test equipment.
The refrigerant line set is like a liquid filled thermometer, it responds proportionately to the change of heat energy added or removed, not so with air measurements.
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By supply, are your referring to a distance down stream of the evaporator coil?
I think he means the air coming into the unit, or the “return”
So do I.
Do you mean the temperature rise between the air coming into the condenser (outdoor coil) and the air being discharged out of the condenser (outdoor coil) … or perhaps you are talking about the temperature rise of the refrigerant, which most specialists will check, but that split/rise would be much higher.
As a rough guide many HVAC specialists will check that the larger suction/return line feels very cold (like a cold can from the fridge) and that the smaller liquid/supply line feels very warm. A considerably greater temperature rise than 15 to 20 degrees, which is the split commonly used to roughly check the temperature drop across the indoor coil (after it’s been running for a while, and as long as it’s not extremely humid or dry).
See the attached diagram from the old TOD for a pretty good schematic of an AC system, with some very rough system temperatures.
Any HVAC specialist worth his salt wouldn’t even hesitate grabbing the gages and thermometer to check superheat/subcooling … but that is well beyond a typical home inspection.
yes you are correct.
Yes Robert very rough I don’t agree with some of them at all.
I have to go get my HI CE tonight and I think this thread will grow by the next time I look. Good Luck
Call me when you guys are in town, Im buyin. I’ll show you guys some differential temp down here in DECEMBER.
Mark why would anyone in their right mind want to come to NY especially in December:p 
to many people.
Your cohort in crime will be there! :twisted:
http://www.grinchmusical.com/?gclid=CJ3Dkf7T1I4CFQ5YgAodjwoM6A
man that was hilarious…I clicked the link but looked away and then heard the song…still laughing!!~!