Turning Off AC

[Pitter]

Sometimes I forget to turn off the AC before pushing the engine stop button so it comes on when I start the car. What is the negative impact of this?

 

[HyFlyer]

Short answer No negative impact. Longer reasoning answer....

Seems like in this day and age of computer controlled everything on the car, all pushing (or not pushing) a button does is let the computer (ECU BCU etc) know you want something to happen ... i.e. turning the headlight switch on tells the body control unit you would like the lights on and it makes it happen. Not like in the old days where you were energizing a relay that powered the lights. Same with the AC switch. I don't believe the BCU will allow it to start the AC process if something bad was going to happen.

I could be wrong. I'm not an automotive engineer. Just a little knowledge guided by experience.

 

[Pitter]

Thanks for that. Good info.

 

[mazdadude]

For myself, I prefer to run the car without the A/C for the final 30 seconds before parking and turning off the car. This allows more of the condensation to be blown off of the A/C coils and drip tray, preventing mold, mildew, and the "musty" smell upon next use.

 

[Gozo]

For myself, I prefer to run the car without the A/C for the final 30 seconds before parking and turning off the car. This allows more of the condensation to be blown off of the A/C coils and drip tray, preventing mold, mildew, and the "musty" smell upon next use.

I thought I was the only crazy OCD person that did that! But I also leave it on recirculate so as not to suck humid air in and add to the condensate.

 

[VQ35DE]

For myself, I prefer to run the car without the A/C for the final 30 seconds before parking and turning off the car. This allows more of the condensation to be blown off of the A/C coils and drip tray, preventing mold, mildew, and the "musty" smell upon next use.

Same here.

 

[DwightFrye]

I also shut off the AC a couple of blocks from home, mainly to minimize any water dripping onto my garage floor. When out doing errands, etc. I always shut off the AC before shutting off the engine but I think that is just an old habit from the days when it put more strain on the starter to crank the engine with the AC compressor on. Those old AC units from the '70's through '90's did make a noticeable difference in engine power when turning on and off. Today they are much more efficient.

 

[AVC]

Some thoughts; the PCM doesn't enagge the AC compressor until the engine starts and reaches stable idle--typically a few seconds. Forcing the system to run in RECIRC all the time tends to INCREASE the likelihood of mold/mildew in the evaporator, as it recirculates any spores in the cabin and your sour C02, off-gassing breath and fart residue, and concentrates it in the cabin filter, rather than moving fresh air through the HVAC system, through cabin and out the back of the car. Once the cabin cools down and the PCM *wants* to switch to fresh air, it's best to let it. The best thing you can do to prevent mold/mildew is to keep your cabin filter clean.

 

[Mazdiod2]

Some cabin air filters have activated charcoal, some don't. Wouldn't this affect the filtering efficiency of sour CO2 outgassing and farts?

 

[erhayes]

I'm with mazdadude because I turn off the AC compressor off, leaving the fan on Rec for the last 30 seconds of driving.

 

[CX5_Driver]

AC being smelly discussion notes

AC smell	Various related discussion		https://tinyurl.com/wbmum5s	https://tinyurl.com/t9ptw4m		https://tinyurl.com/saq2jdk		https://tinyurl.com/ydbxxxqe
AC smell	Klima cleaner nextzett 96110615		https://1z-usa.com/klima-cleaner-professional-application/
AC smell	FJC 5914 Foaming Evaporator Cleaner		https://www.amazon.com/dp/ (commissions earned)
AC smell	Lubegard 96030 Kool-It Evaporator and Heater		https://www.amazon.com/dp/ (commissions earned)

 

[AVC]

Some cabin air filters have activated charcoal, some don't. Wouldn't this affect the filtering efficiency of sour CO2 outgassing and farts?

Yep,activated carbon is pretty effective, until it's full of farts and of gas, then they start to have a funky odor.

 

[AVC]

Every OEM since the 1960's (?) is well aware of the downside to running MAX AC (RECIRC) all the time. Many owner's manuals have a note about not using RECIRC or MAX AC all the time. And many, like Mazda, design controls or systems to discourage it; i.e. the manual temp knob does RECIRC only if left fully CCW at MAX AC. The automatic systems will return to fresh air after reaching set point. I've never watched it, but it may cycle to fresh occasionally, even if manual RECIRC or the Auto setting calls for max cooling in order to maintain set point.

 

[GAXIBM]

I have heard that even set at RECIRC a significant amount of fresh air is mixed in due to the need to keep the cabin slightly pressurized to avoid engine fumes, leaking exhaust fumes etc. entering the cabin. I think it is somewhere in the safe design requirements for autos and some fresh air comes in even in the off position.

 

[AVC]

I have heard that even set at RECIRC a significant amount of fresh air is mixed in due to the need to keep the cabin slightly pressurized

Probably some (you'd have to study the HVAC mix box and ducting), although in many cars very little outside air is brought in in that mode; i.e. how quickly your breath fogs the windows on a cold morning if you switch to RECIRC, without AC.

 

[DwightFrye]

The only time I ever use recirculation with the AC on is if I get behind some guy driving a diesel brodozer that is spewing exhaust fumes or something similar.