Defrost recirculating

Why is it when I go to warm up my truck in the a.m. I can’t select the recirculating air button. I can it just doesn’t light up unless it is off defrost. I also don’t believe my electric heater works. Can’t remember what that’s called. Just one of those weird little things I can’t put my finger on.

 

I don't know for sure, but the Defrost function probably locks it out to pull in outside air since that is typically drier than inside air? Just like you cannot turn off A/C when any Defrost level is used (the last three clicks of the knob). I would like to have full control over the A/C function, but. . .

The PTC heater is not very strong, but nice to have. The temp knob needs to be on max and the fan has to be on a setting other than Off for it to work. Also, it stops working when the coolant hits a certain temp.

 

I think there hass been a thread or two about this where people tried to figure out a work around or not. Don’t quote me, but I don’t think there is a way around it. I haven’t seen these threads in a while though.

 

I’ve never seen a vehicle that would do that. My theory has been that on recirculate it’s drawing air in from the defrost vents so it couldn’t blow out there too.

 

The electric heater element should activate when you turn the temp control to max and turn on the fan, if not check your fuse box. EDIT: Check the thread titled "Electric Heater Element?" for details.

 

Sorry, but no. The recirc intake is not the defroster vent. If it were, no air would blow out to defrost the window.

Here's the schematic:

 

You may not be able to select defrost only with recirculate, but you can select defrost and footwell along with recirculate.

This also works well for dusty or smelly outside driving conditions.

 

This was true on some older vehicles. Not the Tacoma from what I've seen.

 

Yeah. I pop on recirc when driving behind pre-DEF diesels and sometimes smokers.

 

Interesting. That is a new one for me.

Do you have any examples, out of curiosity? In the cars / trucks that I have driven, I could always see the defroster vent pattern reflected on the windshield where the defroster was doing its best work. Also, any dust would be kicked up by those vents.

 

I know on my 2000 GMC Sierra it did this. If you stuck your hand on the defrost vent on the windshield you could feel airflow when recirculating air was selected. I think GM did that for a bit under the belief that the air coming off the window would be cooler and cleaner than the air from a low dash vent.

I know on my 2015 F150 I can select defrost and recirculation at the same time.

 

Very interesting.

I drove a mid-2000s Silverado for a friend in nice weather once, and he just sold it for an new one. Bummer. I would like to have seen that. It seems like a weird function / feature?

 

It's designed this way on purpose. It draws in outside air to quickly defrost the windows. It won't let you select recirc when in defrost mode.

 

This.

On my first gen there was a graphic informing the driver to only use fresh air when defrosting. That was a mechanical control. With the newer tacos being all electronic, I’m sure Toyota programmed this in to remove any user interaction when defrosters are used.

 

Doesn’t the mandatory AC on when defrosting though make that point a bit mute? I mean the AC should dehydrate the air either way to a pretty low humidity level.

 

Yes. A/C air is drier, but A/C air from the outside is even more dry, most times. Up here, where algae grows on things if they don't move fast enough. . . but still.

 

Don't be sorry, you have documented info, that's what I love about forums like this, everyone has different knowledge and resources to share. Plus now we know it's physically possible. If someone has the time and interest there could be a possible future mod here.

I'll have to try that, could come in handy on humid NC summer evenings.

Ah, see and I used to own several GM trucks.

 

I just don't like stepping on toes in a friendly discussion. In the end, you were right that some cars do used the defroster as the recirc intake.

 

This makes sense to me. I was just curious because I like to try and get my windshield defrosted but with warmer recirculated air. Oh well. Think I’ll live...I hope.

Ok. Should have read other posts. Thanks for all the feedback. Great info here!

 

Hmm was hoping that the schematic would show why the driver side left vent is almost always blowing in every mode on my truck, but I'll not hijack the thread!