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Defrost Not Working On Rx 330


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My Lexus RX 330's defrost will not work. While I'm driving in the rain the whole windshield will fog up, and I literally have to pull over to fix the problem. I think I may have leak, that let's in moisture. Has anyone heard of this problem?

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Does the air seem to be coming out of the defrost vents when it's on defrost? If not, it's probably a problem with an actuator in the Heat/A/C/defrost system. If air is coming from the defrost vents, it may be a leaking heater core allowing the coolant to deposit on the WS. My bet would be actuator failure not allowing the defrost door to open. Even cold air will defrost a winshield, just not as fast as hot.

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My Lexus RX 330's defrost will not work. While I'm driving in the rain the whole windshield will fog up, and I literally have to pull over to fix the problem. I think I may have leak, that let's in moisture. Has anyone heard of this problem?

ALL Lexiis(***) have an issue of sudden windshield fogging, it's often simply the result of the way the A/C compressor is controlled. The best you can do is when the windshield fogs up, or hopefully as it begins to fog up, turn the temperature setpoint UP, to max if enough time, and then switch to defrost(defog) mode.

The second way you can help yourself on this matter is to NEVER make use of the A/C (compressor) unless actual cabin cooling is needed. As of '01 there was a C-BEST option so that you could disable, indefinitely, the A/C compressor by simply switching off manually once. Later RXes, possibly yours, had another C-BEST options that prevented the system from switching automatically into "cooling", dash airflow, mode. In cooling mode there is no "warming" airflow to the windshield to keep the interior surface above dewpoint, the point at which windshield fogging onset begins. Keep your system in "heating" (footwell airflow) mode throughout the cool/cold period, and the A/C OFF and you will be much less likely to encounter a HAZARDOUS windshield fogging event. I try to remember to switch mine to "footwell/windshield" combined when it's raining.

At one time there was an aftermarket DIY modification kit for early LS400 climate control ECUs that would automatically turn the heat demand up with defrost(defog) mode activation. I have never seen one for the Rx series.

*** Any, industry wide, climate control system designed by Nippondenso, or Denso US.

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Jaswood, help me out on this. I don't own a Lexus (only Toyota), the RX is my DIL's. I'm only the mechanic for it. I am not familiar with the defrost problem with the Lexus. For as long as I can remember most all vehicles have the A/C tied in with the defrost. #1, to keep the compressor seals working to keep them from drying out and #2, to enable the dehumidifying affect of the A/C operation to help the defrost picture. For most cars that works well, as it has for decades. What is it about a Lexus that the A/C is COUNTERPRODUCTIVE? Though hot air obviously defrosts the windshield much quicker than cold (not talking about melting ice), COLD air will also defrost a windshield. What about a quick frost up when you 1st start out, all you have is cold air till the heat comes up? I am old enough to remember when cars had a little electric fan mounted at 1 corner of the windshield. It was your A/C in the summer (LOL) and also your DEFROST in the winter.

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Once the system goes into cooling mode Denso makes use, exclusively, of the dehumidification capabilities of the A/C for windshield defogging. In certain climatic conditions, HUMID & COOL, that simply does not work. Or think of cabin HUMIDITY as the result of loading someone WET onboard, wet, sweaty snowskiier, etc.

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