I’m fairly certain that the guys are not 100% correct on the “sound ac strategy” answer. While it is true that modern cars do boost the IDLE speed when the ac is on and it would burn more gas sitting at an idle, some cars (my 97 Civic for one) will cut the fuel when coasting to a stop. You can literally feel it when the engine kicks back in as you get to a lower engine speed while coasting. So… you can, indeed get some AC braking and, theoretically, save a tiny, tiny bit of fuel by manually kicking the AC on and off at the right moments. But, geeze, it just ain’t worth it!
I’ve been hoping someone would start a new thread on this topic.
I agree the guys are wrong, all the guys, including the husband who uses the AC to slow the car.
Modern cars do not have software to increase idle speed when the AC is engaged. What they do is actively monitor the idle speed and adjust as needed. If the AC drags it down then the ECU compensates.
Where the husband is in great error is that turning the AC on and off is very hard on the AC. Most AC systems toggle the compressor clutch only when the AC is turned on or off by the control switch. The faster the engine is running when the AC is turned on the harder the “thunk” as it starts.
I think its best to just use the AC when its needed and quit worrying. AC is not a luxury, it is Life Support.