dodo41: Thank you for your news. I'd like to know what V1 and V2 are please and your mains voltage at the time you measured these voltages.
From now on we will have to see what happens to decide whether to increase V3 or reduce V3.
Your air conditioning equipment has a mains voltage from 198V - 242V. The circuit we found faulty is creating a voltage V3 which is proportional to the mains voltage in your home. For a mains voltage of 220V ac then V3 is as you measured it = 3.64V. If the mains voltage was 240V I suppose that V3 will be 240/220 x 3.64 = 3.97V
If the mains voltage was 200V I calculate V3 to be 200/220 x 3.64 = 3.31V
For the upper mains voltage limit 242V, V3max would be 242/220 x 3.64 = 4V and for the lower limit 198V, V3min is 3.276V
Thus V3 must stay in the range 3.276 to 4 - not a very big interval - for the microcontroller to recognise the mains voltage as within the acceptable band.
At the moment 3.64V is 0.364V above the lower threshold and 0.36V below the upper threshold, or in other words mid interval.
I suppose your hom'es mains voltage is like the UK's - generally the upper level does not change much but on days of heavy network load the voltage will drop a few volts. If anything I think you may have to adjust the trim pot to increase V3 on days of low network voltage - but only time will tell. You knwo how to do it now and of course do measure the mains voltage, V1, V2 and V3 so you know what is happening require an adjustment.
If this is not clear tell me but now I must take Mabel our dog for a walk because she waiting.
