1. Formation or deposition of layers, (HOT AND COLD AIR SEPARATE)
2. The condition of being stratified.
2. A layered configuration.
This happens when you have a low static pressure, and there is not enough air flow.
Things to look for are dirty filters, closed dampers, anything that may restrict flow... Or you can go right back to you blower motor... Maybe is has a turn to turn short and is not spinning as fast as it should.
Recommended velocity's across your coil should be around 100ft/min, all the literature will say 70 ft/min but when you have a plugged up filter this happens a lot quicker.
Remember to replace any AVERAGE sensing element with an AVERAGE sensing element, it will eliminate problems sensing when stratification does take place... Don't be cheap and get a remote bulb sensor, your unit will just short cycle.