When we start the filtering process initially the temperature will be low, as the insulation value is high. But on temperature increases the IR value starts to decrease because the moisture entrapped in the coils are released due to rise in temperature and this causes the IR value to go down. This is the first stage.
Then comes the point where all the moisture is released and then will be no decrease in IR value or rise in the temperature. This is the second stage.
At this point the heaters are switched off. Now the moisture is removed by the oil filters and the IR value goes up and as the heaters are off the temperature decreases. This is the third stage.