Air Conditioner Temperature Split

If a home has an air conditioning system (whole-house unit), you will want an inspector to assess its functioning as part of the home inspection.

The most important thing to measure when determining the efficiency and proper functioning of an A/C unit is the “air conditioner temperature split.” The temperature split is the difference between the temperature of the incoming air, and the temperature of the outgoing air.

The way to determine the temperature split is to turn the unit on and run it for at least 15 minutes. Then, insert a probe thermometer into the inlet and then again at the outlet and measure the difference in air temperature.

If the incoming air is at 80 degrees F and the outgoing air is 60 degrees F, the split is 20 degrees F. The optimal split is between 14/15 and 24 degrees F.

If a unit is malfunctioning, the split registers at less than 14/15 degrees F; however, excessively high splits in excess of 24 degrees F can also indicate a problem since the cooling system is working too well – causing condensation and potential mold growth.

Causes of a Low Temperature Split

If the temperature split is outside the optimal range, first check for dirty air filters and refrigerant leaks. If these are ruled out, several other factors may cause a low temperature split:

  • Broken thermometer: a broken sensor will send incorrect information to the system. An HVAC repair technician can replace the sensor.
  • Bad wiring (overloaded circuit where the unit is wired to, or loose wires within the unit): contact a licensed electrician for hardwiring, or your HVAC repair tech for wiring within the unit.
  • Condensation within the unit: an HVAC tech can adjust settings, and fix faulty installation.
  • Malfunctioning fans: an HVAC tech can repair or replace fans within the unit or whole-house system.
  • Dust, pet hair, or other debris that has made its way past the filter: make sure the right filter is properly installed and clean; vacuum out the debris and reinstall a clean, properly sized filter.
  • Broken compressor: an HVAC tech will evaluate and repair/replace the compressor.
  • The unit is frozen. Yes, this actually happens – it’s the evaporator coil, not the entire unit, that is frozen and it’s usually due to condensation. Turn the unit off, let it thaw, remove the ice and any lingering moisture, and turn the unit on after a short time. If it does it again, consult with an HVAC tech.

Just as much of a concern is a high split over 24º F, which is an indicator that the unit is actually cooling too well. This can potentially cause condensation and mold growth in the air vents, posing a health hazard. A high split can be caused by:

  • Dirty air filter
  • Improper ductwork
  • Refrigerant leak
  • A fan that is moving too slowly or is the wrong size for the system

Finally, if the inspection reveals any musty, moldy or foul odors coming from the vents, this is a serious health hazard that can be remedied by a thorough cleaning of the vents, and replacement of the air filter.

Videos on HVAC Maintenance and Repair