Windshield Defrost and Air Conditioning...

Noticed today that the A/C did not come on when I went to select the windshield defrost. Manual states something like....at times you may have to select A/C when using the defroster for the front windshield. I can not remember if the 4Runner automatically turned the A/C on or not, thought it did.

Outside air temperature was about 30 degrees F.

Is there some type of threshold that limits the usage of the A/C when selecting defrost?

Truck is a 2019 model year.

Thank you for any info!

 

In normal A/C operation, there is a sensor that monitors the temperature of the evaporator (the cold coil that is inside the vehicle that chills the air). If the evaporator gets to freezing temperature, the sensor tells the compressor to turn off in order to let the evaporator warm up above freezing (and a side benefit of a little better fuel mileage while the compressor isn’t sucking 5 hp from the motor). This prevents the evaporator coil from icing up and eventually blocking all the air flow. Once the coil warms up a bit, the compressor will turn back on. Depending on how fast the air is flowing over the coil, and what the temperature of the air is, this “compressor cycling” could occur every couple of minutes or never. When you mentioned ambient air temp of 30°, sounds like the compressor is deliberately not turning on due to the low temp. If you turn recirculate air on and warm it up inside, the compressor should come on and dry out the inside air an windshield.

 

Thank you for your reply. I went out earlier this afternoon, temperatures in the mid 50s, turned on the windshield defrost but still no A/C light. Curious as to what others notice as well.

 

I haven’t used my defrost much. I have noticed a little quirkiness with whether the A/C light comes on or not, that seems to be dependent on whether recirculate is selected or not. I just poked and adjusted stuff until it came on, but didn’t pay much attention to what I did.

 

Try pushing that a/c button and see if it comes on then ?

 

I think the AC comes on and off in defrost mode automatically but the AC light won’t necessarily light up. That’s how it was in my Tacoma.

That said, something in the 4runner is different than the Tacoma. And I haven’t figured it out yet. I know for certain that there are times the AC light is off; and in my mind (based on my Tacoma experience) the AC light should be on. But instead I have to manually push the AC button.

So, there’s definitely a difference between my 2nd gen Tacoma and 5th gen 4Runner. Even though the controls are all identical (in function), the behavior of the AC light is different.

I could probably figure this out by reading the drivers manual, but nah... it hasn’t pissed me off yet. Tick tock.

 

Mine always turns AC on with defrost....

 

I’ve always been under the impression that the AC is on when defrost is selected but the ac light simply doesn’t turn on (so as not to cause confusion).

But maybe you guys are correct in that ac actually cycles on/off as necessary (that makes sense now that I think about it).

But as far as the AC light goes in other modes, I’m stumped. Maybe if the compressor is on when in defrost and you turn the dial to a different setting, the AC light comes on. But if the compressor isn’t running in defrost mode, and you switch out of defrost mode, the AC light will stay off.

 

Yes, I can engage the A/C in defrost mode by pressing the button. I could have sworn it (the light itself) used to always come on automatically though. Wondering what others are seeing?

Thanks for the replies!