AC Splits Yea or Nay

[David A. Andersen]

I would like to amend my posting a bit.
I take splits!
I take them at the registers too!
That IR Thermometer is great! But, not trust worthy. It is accurate for temp differential (for what we need it for). I won't leave home without it!

Taking splits is like looking out the window and predicting the weather!
Accurate? No, but a good place to start when trying to decide what to wear to your inspection.

Get the drift?
The more information you add to the equation, the better chance of it to be accurate. Just don't use it as the sole basis to get the HVAC guy out there.

Use it all.
1.Look at the suction line. Is it wet? If not, it's not below the dew point. (For you guys in AZ and arid climates may not get wet because of your "dry heat" that everyone talks about. Go to step two).
2.Feel the suction line. Is it cool? Do you see frost anywhere?
3.Feel the liquid line. Is it hot? Also feel the air discharging the condenser. If you feel a lot of excessive heat, it may be dirty and restricted air flow.
4. Is there condensation discharging from the unit. This means it's working on latent heat. It will be there in large quantities even when the supply air is high and your split reading is out of whack.
5.Take your temp splits.
6. Take supply air temps close to and far away from the a/c unit. This differential tells you about attic ventilation (if the duct is in the attic space).
7. Take temps at every register. One register with extreme rise or fall in temp is an air distribution indication. In A/C an excessive cold register is an indication of LOW Air flow (everything is backwards in HAVC!).

[Bill Smith]

Great posts guys - very informative.

2.Feel the suction line. Is it cool? Do you see frost anywhere?
3.Feel the liquid line. Is it hot? Also feel the air discharging the condenser. If you feel a lot of excessive heat, it may be dirty and restricted air flow.

How long should the system be running in 75-80 degree weather for these parameters to be relavant?

[Roy D. Cooke, Sr]

I do take splits to get some idea if it needs service or seems to be doing what it is designed to do .
Our AC units last about 16+ years as they are not used as much as southern areas.
Our ouside units are usually mounted on a patio stone and the biggest cause of low efficiency is BOY DOGS destroying the fins with their showing that this is their area. They pea on them!!!!!!!!
Roy sr.

[David A. Andersen]

Bill, If you are just turning on the A/C, 15 min should do it if it's not too hot inside. I turn the a/c way down to keep me cool with all my gear on while I do the inside.

If the indoor temp is about set point and the unit is set to cool and had been running it takes no time (5 min) to be sure.

Roy, Are you sure it's the dogs?

[Roy D. Cooke, Sr]

Originally Posted by dandersen

Bill, If you are just turning on the A/C, 15 min should do it if it's not too hot inside. I turn the a/c way down to keep me cool with all my gear on while I do the inside.

If the indoor temp is about set point and the unit is set to cool and had been running it takes no time (5 min) to be sure.

Roy, Are you sure it's the dogs?

I have to thinks so it is only on the bottom 6± inches.
It could be the owner I guess if he gets on his knees .
I never thought of that.
Roy sr

[jmcclure1]

You can't just walk into a house, sub cool a unit and expect a proper reading.
You should just superheat it while your at it.

[Dale Duffy]

Originally Posted by bsmith

Great posts guys - very informative.




How long should the system be running in 75-80 degree weather for these parameters to be relavant?

Bill,

When its 75-80 degrees here I still have the furnace on......

[Carl A. Brown]

Is your blood really that thin Dale? It must be nice until it gets hot!

[JLilly]

I do look at the deltaT but I also put a gage on the system.

[hspinnler]

An HVAC contractor called one day to vent to me about how we home inspectors take the readings with a laser thermometer of the duct temperature rather than taking the temperature of the air itself at the supply coil and return plenum. I modified my approach by switching to checking for ambient air temp instead of checking the surface of the duct or register. There's a big difference in readings depending on whether those ducts are located in a hot attic or are located far away from the air handler. Now, I go to the source.

[JLilly]

The infrared thermometers don't handle reflective surfaces well. When I take a reading off a pipe I first but some black tape on it. Metal duct will give you a bad reading.

[David P. Valley]

I try to stay as close as possible to the unit, when taking readings from the supply and return.

[gbeaumont]

Hi to all,

Delta-T really does not tell you anything much at all as there are way too many variables in play.

• Type of system (heat pumps always low)
• Efficiency of system (older = lower)
• Type of ducts
• Condition of ducts
• Length of ducts
• Is the system balanced
• Is the filter clean
• Is the charge full etc etc.

The better way to check for system efficiency is to take an amperage reading on the compressor, and visually check for condition of ducts and state of filter.

Regards

Gerry

[Roy D. Cooke, Sr]

Originally Posted by gbeaumont

Hi to all,

Delta-T really does not tell you anything much at all as there are way too many variables in play.

• Type of system (heat pumps always low)
• Efficiency of system (older = lower)
• Type of ducts
• Condition of ducts
• Length of ducts
• Is the system balanced
• Is the filter clean
• Is the charge full etc etc.

The better way to check for system efficiency is to take an amperage reading on the compressor, and visually check for condition of ducts and state of filter.

Regards

Gerry

If I get a 2ø to 4ø split I am concerned and write as needing further evaluation.
If I get a 12ø to 20ø split I feel that is doing what it is designed to do .
Roy SR

[gbeaumont]

Originally Posted by rcooke

If I get a 2ø to 4ø split I am concerned and write as needing further evaluation.
If I get a 12ø to 20ø split I feel that is doing what it is designed to do .
Roy SR

Hi Roy,

That is really the only use TD is as one of the indicators at best.

Even in your ranges an older heat lump system running at 8-12 degrees delta T may be performing as well as it did when installed, that is the point I was trying to make.

Regards

Gerry