I need to design a circuit to use in my car to control the A/C such that whenever the car stops for more that 5secs, it should turn the AC off and switch it back on 5 secs after the car starts moving again.. To make things simpler input can be taken from tail brake light such that applying brakes for 5 secs turns it off.. The AC power button is a micro switch and I intend to connect a 12v relay with this switch with the N/C connected in series. Could somebody help me with the simplest ideas?? I intend to unload the engine when the car idles at traffic signals..

 

That doesn't make too much sense, really. When the vehicle is stopped, about the only useful work the engine is doing is running the A/C and keeping the battery charged.

What would make more sense is to monitor engine vacuum; if it is low (say below 15inHG or so) then the engine is working harder, meaning the vehicle is accelerating, so if the A/C compressor were cut off, their would be more power available.

You could pick up a few MAP sensors from a junkyard and experiment with them.

 

Is there something wrong with the engine where it stalls at idle when the A/C is running?

 

Engine is fine, I want to state first of all that it is a diesel car. And as diesel engines are weak when taken with the size to bhp ratio, just wanted to get that pick up which is necessary at stop and go. Diesel engines are economical but not powerful. And also as the car is under warranty, i cant go hacking in too deep when its under cover. The setup I described would be easy as plug and play, matter of only a molex connecter to the fusebox and nobody can guess what it is.