Och

iTrader: (3)

So I've had this issue with my heater ever since I got the car, but I never bothered to figure it out. Here's the deal.

First of all, I usually set my temperature to 72 degrees in the summer and in the winter and I set my vents to blow from the dash and the floor. In the summer time, there are no issues, the AC works nicely and 72 degree keeps the cabin comfortable and not too cold. Of course, if its really hot outside, I just set it to max cold.

Now, in the winter its a different story. When I set it to 72 and the cabin is cold, both the floor and dashboard vents blow warm air. However, as the cabin warms up and becomes comfortable, the dashboard vent starts blowing cooler and cooler air, while the floor vent keeps blowing warm air. Once the cool and warm air from these vents mix, the overall temperature in the cabin is nice and comfortable, but the cool air blowing directly at me from the dash vents does cause some discomfort. So then what I do is set the temperature to 75, which makes the floor vent blow even warmer air and dash air also warms up, however once the cabin reaches warmer overall temperature, the dash vent blows cool air again but floor vent keeps blowing warmer air. If I raise the temp to about 80, the air that blows out of dashboard vent never drops to be uncomfortable, but the problem is, floor vent is blowing air that is way too hot.

My understanding is that there is a cabin temperature sensor underneath the steering wheel, that lowers the temperature of the dashboard vent air as the overall temperature of the cabin goes up. But why does it lower it so much, and how come the floor vent isn't being affected?

Amskeptic

Because you are experiencing what Toyota knew of "stratified climate control" circa early 90's. And the Program will tell you what you need and your opinion is not relevant to the Program, now is it?

I noticed exactly the same thing and found a couple of workarounds.

A) Throttle back the driver's and center vents 50%. Now the cool stratification is less, so it won't trick the temp sensor into pumping so much footwell heat. Use defrost/floor switch if you still feel the draft.

OR

B) Knock down the temp display from 75 to 70 once this stratification occurs, and things often level out nicely.

OR

C) Open a front window and you get some fresh air and the blast makes the stratifier think things are still trying to warm up.

This is a weak moment in Lexus engineering. My BMW let YOU set the stratification cooldown to exactly what YOU like. More power to the people . . .
Colin

Och

iTrader: (3)

Thanks Colin. I guess then its normal, just programmed this way. Just for the record, this doesn't happen with my other two Lexus, the air from the dash vents stays warm enough not to cause any discomfort.

I appreciate the workaround suggestions, what I've been doing is actually pointing the dash vents away, so they don't blow cool air directly at me, and this way there isn't much discomfort.

I'm planning to do the following experiment, I want to remove the cabin temp sensor from the footwell area, extend the wires and relocate it somewhere higher up, and see if that may improve the overall comfort.