Need assistance with understanding a car.

I recently purchased an used 2004 Lexus IS300. Whenever I turn on the fan for heat/ac, the AC light automatically turns on regardless of what temperture I set. I was wondering if it's cold outside and I turn the temperture to 80 degree and turn on the fan, if the AC light is on, what will happen? Does it waste freezeon(??)? Will I not get the 80 degree I desire? Thanks.

With the air conditioner on and heat selected, the cars ability to remove moisture from the passenger compartment is increased. example : windows fogged on a rainy day, without a/c selected, it will take longer for the climate control system to remove the moisture from the windows. Running a/c along with heat will not hurt anything.

Then that means I will not get the 80 degrees I desired since the AC cools down the heat, right? As for moisture/fogged windows, couldn't I just turn the degree down and use "fan" only instead of AC? Or does AC + Heat is a better way to clear moistures?

Conditioned air is drier, so the fog will clear much faster. In most cars the AC compressor comes on when the defrost/defog mode is selected. I'm sure there must be a way to turn off the compressor and still use the fan. Check the owners manual.

Geoff

As was stated earlier most cars use the A/C for removing moisture when using the defroster. That does not mean that the A/C runs the air cold enough to overpower the heater core. Why not try it and see if it will heat the interior to 80 F? Seems like a high setting to me but whatever makes you comfy.

Like Flying Turtle said the A/C light might be coming on only when the heater is set to defrost or turned so that the fan vents at the windshield. I don't know about Lexus but as I recall most of the cars I have seen do not use the A/C under regular heating settings. Again, did you check the owners manual?

Obviously on a very cold day no car interior will heat up instantly from a cold start but it should get warm enough in just a few minutes.

As for just using the fan to defrost or demist the windows, that won't work as well since you are not removing the moisture from the air inside the car (at least not very fast). The A/C removes mositure quickly.

The heater core has far more capacity to heat than the A/C evaporator does to cool. You'll easily be able to reach 80 degrees with the A/C compressor on. Without running the A/C when the heat is on, to me, it feels like I'm in the tropics - very wet and humid. I dislike this in the car so I always run the A/C with the heat.

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RBR said:

Some cars start the A/C as soon as the fan is set to the windshield, also on mix positions, to minimize fogging as the conditioned/dry air, even if (set to) relative cold, from the A/C will

RBR

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My setting is not set to the windshield. Its setting is set on the driver.

jinx626 said:

Whenever I turn on the fan for heat/ac, the AC light automatically turns on regardless of what temperture I set. I was wondering if it's cold outside and I turn the temperture to 80 degree and turn on the fan, if the AC light is on, what will happen?

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Just hit the button to turn it off. I see that you have to switch-by the AUTO setting from off in order to get to the manual fan settings and that may automatically turn on the AC. Just turn it back off if you don't want it on.

If this is the case, rather than having to turn the AC back off all the time, I'd just leave the fan on Low all the time, and manage the AC button manually.

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You'll find Lexus uses some pretty complex algorithms for their climate control; if you just set your temperature and let the car do the work, you'll find it'll get to your set temp quickly and remain there very steadily.