How to conduct a temp split test ?

Old 06-06-16, 01:05 PM
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How to conduct a temp split test ?

Cutting a long story short, i have an Goodman AC system that was installed in 2009, that had its coil replaced in 2013. I posted a thread about cleaning the coil here.

I've since cleaned my coil, firstly using a shopvac and stroking downwards with the fins which sucked up my best guess is about 75% up, (cos you can only see the surface of the fins, which are around 5" deep) Anyway I then went about using some Pro-Clean indoor Coil Cleaner mixed at 3:1 that i picked up from an HVAC store. I sprayed 32oz of fluid all over the inside of the coil, then flushed it with around 64oz of water. All of which pretty made its way out via the AC drain, and fortunately not into my face as i was directly underneath the unit. Don't worry i was wearing protective googles I also wiped away as much of the black dirt and mold as possible using an entire pack of baby wipes in all other areas of the AC unit. Then this morning, i gave the coil another spray again at 3:1 with the coil cleaner, though this time without flushing it. AC unit is actually looking pretty clean. Much cleaner than when the last tech left, who literally did nothing more than take measurements and try and sell me some extra services... A clean like i just did for $400 or a coil pull for $1600.

Anyway during the service he took the following measurements.

The temp split start was 64/78/14
The temp split finish was 64/74/14

Using a thermometer that was stabbed into the cold air return duct.

Not sure exactly on the procedure, but i'd like to re-conduct that test to see how effective my cleaning was. I'll go buy a thermometer. Just need to know what to do to properly test. I think he turned it right down, and left it for a matter of time... Trying to read into the numbers provided.

He said my measurements were just ok at best because of the amount of dirt in my coil.. The rest of the system apparently checked out well.

Anyway any advice appreciated. Thx
Old 06-06-16, 02:55 PM
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I assume the 14 is the temp split. The finish temp split is 10, both too low. Take temp at supply duct near the furnace and return duct near the furnace.
Old 06-06-16, 03:28 PM
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Have you cleaned condenser coil recently?

A dirty evaporator coil will tend to give you a LARGER temperature drop.

Colder air, but less volume.

Has your evaporator coil frozen? If your condenser is dirty, this is less likely to happen to a dirty evap coil, since pressures will run higher since it has same problem as evap...It can't transfer heat efficiently.

This will also trick bad techs to ADD refrigerant, which is step 1 to blowing up the compressor and using lots of electric.
Old 06-06-16, 07:28 PM
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Simply put the thermometer 1 inch from the return air vent, get the temperature reading, then move the thermometer to a cold input air vent, 1 inch from the vent, choose a vent near the furnace. After 5 minutes, get the cold air temperature reading. The difference between the 2 readings will be your split. it should be at least 15 degrees.
Old 06-07-16, 07:32 AM
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To evaluate an indoor temp-split - get an indoor % of relative humidity reading

The temp-drop is directly affected by the ndoor humidity level; higher the humidity above 50% the less drop; below 50% drop increases as humidiy level falls.

At 50% indoor RH drop should be around 19 to 20F.
Always record the indoor humiity level & list it with the drop& other numbers...

Also check the condenser air discharge temp above oudoor temp & the SEER number of condenser. That indicates if it's removing the proper amount of sensible + latent heat...

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