I have Carrier Durakool Air Conditioner 1.5 Ton. What happes sometimes is that out the blue, while running, the conditioner shuts down and on the display an error message is see E7. After couple of hours, and after restarting, AC works fine again.
What is this? Why does it come? How to go about this?

I don't know the E7 code but it sounds as if it could be one one these problems. 1) the motor is shutting off on it's internal overload and after it cools it resets and starts up again 2) it is going off on low pressure switch due to low refrigerant and when it stops and the pressure equalizes it resets and stars up again or 3) the high pressure switch (but normally this would have a reset button) It shuts down the unit if pressure gets too high. This problem could be cause by overcharge or dirty evaporator or condensing coils. Has the unit been taken out of it's case and cleaned very well recently? Is the filter clean? I looked for the code but cannot find it. Best of Luck