Weird Heater Issue

My 05 taco just started doing this and I can’t find anything related.

When I change setting to defrost (windshield) no hot air comes out of the vent and the air circulation light turns on and engine temp rises.

when I change setting back to hands/feet hot air blows just fine, engine temp returns to normal and I can turn off the air circulation.

anyone got any ideas?

 

Watching. This is a good one

 

When in defrost mode the A/C kicks on without lighting the A/C light so I wouldn't expect hot air to come out of the defrost vents that's equal to the hot air of any other vents when the A/C is off.

How well does your A/C work?

 

A/c works great. When I say no hot air comes out of windshield vent I’m talking cold air with no hint at warmth. Air re circulation light which normally you can’t turn on when turning on defrost turns on and you can’t turn it off.

 

Not familiar with that. Do you mean the re-circulation light?

 

Yeah the recirculation light

 

I wondered if that was normal - air conditioning being on but the AC light is not. I know air conditioning activates in defrost mode, because it'll clear up any condensation on the windshield. I wondered how that will work in cold weather (haven't had my Tacoma in very cold weather yet) - is there no way to turn the air conditioning off in defrost mode? I know with previous vehicles I've had (Hondas) the air conditioning and AC light would turn on in defrost mode, but could be manually deactivated.

Also what's strange about the OP's situation is recirculation light turns on, when it should turn off. That, and the engine temperature increasing.

@tacotez - when using the air conditioning through the dash vents does the engine temperature increase?

 

That is for sure a strange issue, the recirc light coming on in defrost could suggest a failing A/C control or A/C Amplifier but the engine temp rising when on defrost is very interesting.

Yes it can be with a simple wiring mod at the mode servo, I did it on mine years ago.
https://www.tacomaworld.com/threads/a-c-on-with-defrost.7160/

 

Re: Manual AC control in defrost mode -

Now that's interesting! Good to know, thanks and saving for reference.

 

At least check the coolant level

 

That’s an interesting set of symptoms. I think you’ll want to start by checking whether the ventilation actuators are moving into the correct positions. @Dm93 has a couple of pictures marked up that show the normal positions, you can refer to this post. If air is blowing out the windshield vents then the vent selection actuator is probably working fine, so the blend actuator should be checked as you adjust the temperature control. The fresh/recirc flap position too, of course,

The recirc light is interesting, makes it seem like an electrical fault. Perhaps one that causes the light to illuminate, and the blend actuator to pass only cold air?

For the “engine temp rises” part, I wonder if you have a temperature sensing device that would let you verify that the engine temp is indeed rising? I can’t imagine that an electrical fault in/around the ventilation controls could affect something in the instrument cluster, but this is such a curious mix of symptoms that it seems worth verifying or ruling out.

 

As equipped there is not a way to turn the A/C off when in defrost mode.

My bet is on the OP's heater control going out. I've also read on TW of heater control plugs/wiring getting too hot and requiring replacement, but I personally haven't seen it, so the OP should probably take a look at that as well.

 

@tacotez it's been over 3 weeks. No more diagnostics or a resolution to share? We kinda enjoy seeing people conclude what they started. So we can all learn. Don't leave us hanging dude!

 

Sorry to say this isn't and answer to the problem, but it might help. In every automotive A/C system I have ever known or worked on: the evaporator within the system is in series -before- the heater core. The air is dehumidified before it moves through the heater core. Cool the air/warm the air unless the dial is set to full cold. The idea is to remove the moisture before it travels through the rest of the system to prevent the windows fogging up when the moist air condenses on the colder glass surfaces. That said: another feature in most, if not all automotive systems prevent the engagement of the A/C (compressor) when temps are below +- 40 degrees F. I'm not sure what controls this feature on a Tacoma, (refrigerant pressure switch/sensor?), ambient air temp sensor?, etc. On my 2014 the compressor doesn't run below about 40 degrees no matter what the settings are. I'm not sure if the light comes on when you push the A/C button in my truck in the winter. I never do it. I'm pretty sure, but can't confirm right now, that when the defrost setting is selected and the "re-circ" light comes on, it can be turned off by pushing the "re-circ" button and the light goes out.

Sorry I can't say or imagine what is making your system act like this, other than maybe "old age"? Definitely strange. It seems like the problem is with the blend door/motor. Looking forward to hopefully see the answer on this one!!

 

Sorry guys,

It's been a busy month. I haven't had as much free time since original post.

I figured out that the cold air is not limited to defrost. But I can't recreate the recirc light turning on by itself.
Below 2k rpm heater blows cold air. Leads me to believe it's a coolant issue, but I'm not hearing the slushing sound of running coolant like that last time I had air in the system. Coolant level is full.
When sitting at idle like in the drive through or car wash, temp nearly redlines. I can get the temp to drop by revving the engine at 2500 rpm.

I have not really dedicated any more time to figuring it out since I only need to drive the truck 2 days a week to drive the kiddo 15 min down the road to visit grandma.

Currently debating on just taking it to the shop.

 

Might want to check the thermostst

 

could be. But it was just replaced in 2020

 

New one fail too.

 

If the truck is trying to overheat when idling and not moving, I’d definitely recommend taking a look at the fan clutch. You shouldn’t be able to see it spin very far when you spin it by hand, it should stop again after a small fraction of a turn.

But I have to say, the symptoms sure do sound like low coolant. Or coolant that’s not being pumped through the engine and heater core properly. I have seen a couple of YouTube videos where the water pump has degraded internally and is not pumping much at all. Haven’t heard of it on it on a Tacoma, but I suppose it’s possible.