Front Mirror Heater Problem..

[AhMing]

I got a 1999 second hand RX300. Can anyone tell me how to fix the problem of my front mirror heater. WHen the button is switch on, suppose to blow the hot air to the mirror, preventing the mirror to become blur during raining . But it blow the cool air, and mirror all get blur immediately. It is a second-hand car i just bought for 3 months. At 1st is the air-cond function can't blow the feet area, while the front mirror heater totally no function, no air blow. After send for repairing, air-cond is functional well, but the heater do blow with cold air. If adjust the air-cond to go for blowing hot air, the heater hole will also blow hot air. Hope any expert can give me some help...

[wwest]

I got a 1999 second hand RX300. Can anyone tell me how to fix the problem of my front mirror heater. WHen the button is switch on, suppose to blow the hot air to the mirror, preventing the mirror to become blur during raining . But it blow the cool air, and mirror all get blur immediately. It is a second-hand car i just bought for 3 months. At 1st is the air-cond function can't blow the feet area, while the front mirror heater totally no function, no air blow. After send for repairing, air-cond is functional well, but the heater do blow with cold air. If adjust the air-cond to go for blowing hot air, the heater hole will also blow hot air. Hope any expert can give me some help...

When you manually put the system in full or partial defrost/defog/demist UNTIL the cabin temperature has risen to close by your setpoint, the system will blow reasonably WARM airflow from the interior windshield ducts and therefore keep the interior mirror somewhat defogged. Once the cabin temperature reaches the point wherein the climate control switches, would switch, to the cooling mode, airflow from the center dash area, then it is a practical impossibility to get the system to supply enough warm airflow to keep the windshield defogged let alone your inside rear view mirror.

The best procedure I have found is to put the system, manually, in mixed defrost/defog/demist and footwell air distribution mode, turn the heat up to max. Once the mirror (and/or windshield) is defogged reduce the blower speed to something a bit more quiet and then adjust the heating level downward slowly until you reach a point of human comfort.

Google for:

wwest demist denso

For more information.

PS: I always TOTALLY disable the A/C compressor circuit throughout the winter months. My '01 RX300 has two c-best options that address this VERY issue, I don't know if they go all the way back to '99.

[grouch]

PS: I always TOTALLY disable the A/C compressor circuit throughout the winter months. My '01 RX300 has two c-best options that address this VERY issue, I don't know if they go all the way back to '99.

I believe that most auto manufacturers today have the A/C come on with the defrosters to dry out the air. The default program of most cars is if the H/AC system goes out, it is automatic to def. w/A/C and your temp select controls how much heat you get.

If it's the inside mirror that is fogging up, then get some "Rainex" anti-fog and put it on.

I was told that Lexus already on the 330's has an anti-fog coating on the windows, I don't know if that applies to the 300's. If you smoke, it means you must clean the inside more often as the coating attracts smoke.

[wwest]

PS: I always TOTALLY disable the A/C compressor circuit throughout the winter months. My '01 RX300 has two c-best options that address this VERY issue, I don't know if they go all the way back to '99.

I believe that most auto manufacturers today have the A/C come on with the defrosters to dry out the air. The default program of most cars is if the H/AC system goes out, it is automatic to def. w/A/C and your temp select controls how much heat you get.

If it's the inside mirror that is fogging up, then get some "Rainex" anti-fog and put it on.

I was told that Lexus already on the 330's has an anti-fog coating on the windows, I don't know if that applies to the 300's. If you smoke, it means you must clean the inside more often as the coating attracts smoke.

The efficiency of the A/C for dehumidifying the incoming fresh airflow is a function of the local climate. Therefore the safest and most relaible method of quickly defogging the interior surface of the windshield is to use MAX HEAT, MAX BLOWER SPEED, FRESH inlet airflow in defrost/defog/demist mode. years ago it was quite reasonable to turn on the A/C since it might accomplish at least some minor level of dehumidification and thereby be an aid in defogging the windshield.

Today's HIGHLY efficient cooling evaporators act much like a sponge. So once the A/C is switched off the cabin will often be FLOODED with the previously accumulated condensate as it now evaporates into the incoming airstream.

So, use the A/C as an aid for defogging or preventing windshield condensation, but once you shut it off be diligently prepared for the result, even if it was yesterday when you last switched it off.

See:

http://airsept.com/index.php?loadmod=eed

[AhMing]

Thanks for the reply. My situation is,when there is raining day, i only can set my air-cond to warm tempreature, even though outside temperature is average(around 23-24'c). It seem like the switching on of heater will only change the air-cond setting to blow the feet area, and start blowing cold air to front and side mirror through heater ducts. I doubt it is something with electronic or mechanical problem of the car, since the air-cond have been send for repairing before. The heater blow the same air as the air-cond.

[grouch]

The efficiency of the A/C for dehumidifying the incoming fresh airflow is a function of the local climate. Therefore the safest and most relaible method of quickly defogging the interior surface of the windshield is to use MAX HEAT, MAX BLOWER SPEED, FRESH inlet airflow in defrost/defog/demist mode. years ago it was quite reasonable to turn on the A/C since it might accomplish at least some minor level of dehumidification and thereby be an aid in defogging the windshield.

Today's HIGHLY efficient cooling evaporators act much like a sponge. So once the A/C is switched off the cabin will often be FLOODED with the previously accumulated condensate as it now evaporates into the incoming airstream.

So, use the A/C as an aid for defogging or preventing windshield condensation, but once you shut it off be diligently prepared for the result, even if it was yesterday when you last switched it off.

See:

http://airsept.com/index.php?loadmod=eed

You learn something new everyday.

[wwest]

Thanks for the reply. My situation is,when there is raining day, i only can set my air-cond to warm tempreature, even though outside temperature is average(around 23-24'c). It seem like the switching on of heater will only change the air-cond setting to blow the feet area, and start blowing cold air to front and side mirror through heater ducts. I doubt it is something with electronic or mechanical problem of the car, since the air-cond have been send for repairing before. The heater blow the same air as the air-cond.

When you say "mirror" do you by any chance mean to say WINDOW...?

The left and right outside rear view mirrors are heated using electric resistance heating. They are on the same control circuit as the rear window resistance heating.

But yes, due to a unique aspect of the climate control design when you have the system in bi-level air distribution the footwell area will get airflow as much as 20F warmer that the dash outlet airflow. Assuming you have a temperature setting of 72F that 20F cooler airflow temperature will often be somewhat discomforting on a cold day, especially when the radiant heating quotient is in the negative.

The far left and right air distribution outlets aer supposedly for keeping the front side windows free of condensation and therefore the airflow from those is ALWAYS cool, and dry if the A/C is operational and the climate is such that the incoming fresh airflow can actually be dehuimdified. Those two outlets are manually operated so I typically keep them fully closed except in the summertime when actual cooling is desired.