AC cooling temps and return temps?

Specific Inspection Topics Inspecting HVAC Systems
1

Just wanted to get everyone’s opinion on this.
I had an ac in cooling mode where all registers had temps of 63 to 65 degrees and the return temp differential was around 9 degrees I called for further insp. by a lic HVAC tech. Outside temp that day was about 75 degrees.

The sellers agent is questioning me stating thate her ac guy, with out looking at the problem, that I am wrong and he has this prob with alot of HI’S.

Would you have called this with what was stated above.

Thanks.

2

Depending on the system layout, etc. you should be getting something like 15 to 20 degree differential at the register closest to the air handler if everything is working like it’s suppose to.

I think your callout was appropriate.

3

Yeah, the reading that you use is the return vent temp - the closest supply vent to the handler. This should be 15-20 degrees, give or take. Many times you can get a reading from a supply vent far away and it’ll only be 8-10 degrees difference. That’s normal. Use only the number between the return and closest supply. Personally, I only comment when it’s below 10 degree difference.

4

Go back and read this entire thread… This question gets asked about every 3-4 months. Take the word of those who are trained and probably licensed in the field.
http://www.nachi.org/forum/showthread.php?t=3809&highlight=temperature+splits

5

IMHO: I’ve run into this at times…

If you just turn on an AC that was off for a while, and the house is humid, the AC will try to cool down the air, however since there is a lot of moisture in the air the AC will not cool down the air well, but condense the moisture first [latent heat]. Once the moisture is knocked down enough the AC will work harder on actually cooling down the air [sensible heat].

So I run the unit for a while to check it’s performance.

tom

6

If they called me, I would have told them the same thing.
Testing the a/c under a 75 OA Load?!
Just open the window!

I can give you all the reasons why you will not get a split.
I’m leaving town till Tue. so I don’t have time now.

The short of it is…
if you don’t have a refrigerant pressure split, you won’t get an air temp split.
No head pressure and the metering device starves.