A/C ON, NO fog on window.

 

Correct, and when I turn on the defrost I expect it to come on. However, when I turn on the heat and it's 30 out I would not expect it to come on. It also stays on so it's not hitting a humidity point and shutting off. Also did I mention I live in Colorado with crazy dry weather?

My 4Runner and FJ both would turn the A/C on when on defrost but not on everywhere, although I guess they don't have an automatic climate control.

 

I can turn mine on or off.

 

when its on auto, the a/c light will turn on letting you know it will turn it on if needed. but the cabin temp sensor will not let it turn the a/c on if you have the temp selected to be higher then what the temp is physically in the car.

 

I suspect this is the case but I have not been able to confirm it. How did you find this out or are you assuming it?

On our old Camry LE, not auto climate control, if the light was on the compressor was on.

 

Don't understand your problem. There is a A/C icon on the HVAC display where you simply turn it on or off. Read the OM.

 

On my limited, there is a selection in the navigation screen menu where you can customize the A/C function from automatic to manual. This causes the A/C to be off except for defrost or when you push the A/C on button.

 

As everyone has already pointed out, the A/C on is there in AUTO mode.


If the A/C is on and I turn up the heat to max, it blows HOT.
The A/C function is all about humidity removal with the defroster on. It automatically turns on with forward defrost.


After you put it on AUTO and get the heat number selected, push the AC button and it stays off, on mine, anyway.

 

This how it works on my Limited; not sure if it is the same or available on other models:

If you want the A/C to not run in Auto mode, unless you push the A/C button, and only come on automatically when in defrost, here is how to make that happen.

1. Start the car.
2. Push the SETUP button on the dash so the Setup menus appears.
3. Select “Vehicle”.
4. Select “Vehicle Customization”.
5. Select “Climate Settings”.
6. Under “Auto A/C Mode”, change the setting to OFF.

 

If it's 30 degrees outside, even thought it looks like the AC is on, it's blowing out hot air based on the temp you have set. I don't believe the AC compressor is actually engaged when you ask for warm air.

 

I was thinking if the a/c icon was on the compressor was on. Didn't think about it just being available. I may have to check this out and see if the compressor kicks on when it's cold out. It seems like all the other vehicles I've had if the a/c icon was on the compressor was on.
I'll mess around with it in the next few days and report back.

 

I paid attention to my display tonight. It was 32 degrees outside. The car was sitting outside all day at work so the interior was cold. I set the interior temp to 75 degrees on Auto. There was no indication that the AC was on in Auto mode.

I'm pretty sure the compressor only kicks on when the temp outside is hot and you call for cool air for the interior. Then you get the compressor kicking in to refrigerate the air with the AC mode.

I'm not an expert on the HVAC unit Toyota uses, I'm just trying to logically think through when the compressor would really kick on regardless of what the display might show.

 

I'm pretty sure the compressor only kicks on when the temp outside is hot and you call for cool air for the interior. Then you get the compressor kicking in to refrigerate the air with the AC mode.

Doing a bit of research, Toyota is using a variable displacement compressor. There is no on/off clutch. The compressor is always running. When no cooling is required, or if it is below 32f the swash plate is flat and the compressor free wheels. If the green light is off the compressor will always be in a state of free wheel. When the green light is on the system CPU will adjust the swash plate to get the required cooling.

So if the light is on and the CPU thinks it needs to add some cooling the pump will engage at the level required. So even if the green light is on and it is cold out the compressor may not be doing any more work than if the green light was off.

This is now a pretty common technique used in cars today.

 

The A/C kicks on for all defog/defrost mode on Toyotas at least back to 2002. The A/C light doesn't come on, but it is in fact cycling once the coolant temperature reaches a certain level. You should be able to notice the idle speed change every so often any time the compressor is running.

 

That's what I get for (mis)reading the forum after coming back from seeing my daughter at the hospital.