Does anyone know what the temperature difference should be for the ambient air to the air output from the ac compressor?
14 degrees, rule of thumb, delta t between the return and the coldest supply air.
Thanks!
NO!
Climb on board the “I’m full of ****” Certified Home Inspector Club…
You can’t tell a damn thing about the operation of an HVAC unit by dry bulb temperature unless you designed and installed the equipment.
HAHAHAHA I was waiting for Mr. Anderson to chime in.
Mr. Anderson knows too much… 
If only we could all be as knowledgable and proficient…not to mention courteous and well spoken.
Without a doubt, he means well!
If I had the same knowledge and experience in HVAC systems as Mr. Andersen I would respond the same. He has posted on this site numerous times why the split is not a good way to determine a properly functioning system. Please feel free to look for the explanations and then you might understand why he is so passionate about not relying on the split temps.
I was asked last week by a buyers family member who is an HVAC installer what the split was. When I told him he said “Your not putting that in your report are you?”
When I answered “No” he responded good because they are not worth much.
Then why did you even waste time taking it?
I document heat and cooling at registers with my thermal camera along with using it to document water heater operation. I also use it to look at return air. Once that has occured, providing him with the number was a piece of cake. Many of you use a laser thermometer and take a picture of temp to document but since I have the camera I use it as a method to verify operation and response to thermostat. Images may not be in report but in file.
So Mr. Currins, do you report split temps?
Thanks for explaining Jeff.
And, No I don’t, report them, or even take the reading.
Feel free to criticize me all you want but I take them. No home inspector is going out there and basing their entire decision on their reading. It can be useful in conjunction with the rest of the information you have acquired.
If I inspected a brand new system with a pristine outside unit and air handler but it has a 3 deg differential then I am going to suggest it be evaluated.
If I inspected a system with an aging outside unit, a marginal air handler but it has a 15 deg differential I am going to report(in a little more detail) that the system has aging components but was operating within a proper differential. Due to the age of system you should plan and budget to replace.
Or you have a crappy aqua therm rusting to hell with no differential.
It’s not definitive but it can be a piece of the puzzle. I am not going to put in my report the air felt cool or the suction line reminded me that I need to stop at 7 11 after this to get some cold ones. I am also not going to buy specialized equipment for this. If I bought specialized equipment for every aspect of the house I would have an *** ton of tools and I’d be at the house forever using them all.
Mr. Andersen I have read at least 50 of your posts about the issue so I know your about to go ape **** on me.
With the new R410A your readings/philosophy is out the window, IMHO. If it cools, if it works, it is OK. TI is not needed in inspections. Temps change. Anything can, and will, break down at any time. Tomorrow is another day. Details and numerical values, TI pictures just are not needed in inspections; at least here in KC. All buyers and RE’s want to know if it is working. That’s it.
Ok they want to know its working but you did not provide an alternative to know its working except that if it cools it works. How do you know it cool?
Put your hand on the small copper line from the exterior A/C unit. If it is warm, it is cooling. Listen for the exterior compressor, seperate from the blower motor. All exterior A/C units here are on the ground, and accessible. Some cities have cooling units on roofs; tough with those. Of course, exterior temps under 60 are tough to check, and should be disclaimed.
Yeah and put your hand on the big line and if it feels like a cold beer it’s good. You are still taking a temperature differential only at a different location with a less precise tool.
Electronics are not always precise, and fail often. This works for me, and has not failed in 12 years and 5,000 inspections. To each his own.
That is what I was taught 13 years ago and it has kept me out of trouble .
I am not a AC expert ,it blows cold air or it does not blow cold air .
Worked for me .
Trying to simplify air conditioning down to a single function is like asking your doctor if you are healthy based solely on your temperature. To take it a little further, our SOP simply has us verify that the patient is “alive”.
Properly assessing the state of health of an air conditioner requires much more information: superheat, subcooling, amp draw, indoor and outdoor ambient air temperature, fan speed, relative humidity, an understanding of sensible and latent heat, etc. to name some of the information used in an evaluation.
By all means learn all you can, but if all of the components run and you can verify some temperature differential on the refrigerant lines or between the return and supply ducts, you can say it works.