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Q: Heat cycles on and off on 2004 Lexus RX330

When I first turn on the heat / ac unit, the a.c. light comes on. I turn the ac light off and turn the heat temp up. The heat will work for a while and then start blowing cold, almost like the a.c. is on. After period of time the heat will come back on but will go back to cold before to long. Just got the SUV so I have no real history on it. tk
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Best thing to do is to have the Climate Control Computer scanned for codes to see what the root cause of the malfunction is, it could be several things, like an intermittently defective Temperature Sensor etc.
Then you will know, by the way, this is way beyond a parts store scan, this type of Diagnosis on Climate Control is best done by a good Pro shop. An initial Diagnosis should be about $100-150
A mechanic told me to try "cleaning" the sensor prior to a full blown diagnosis. Unlike some other cars I have had that you can see the sensor on the dash I do not know where the sensor is on the Lexus. Any clues? Thanks.
I have been having this same problem with my 2004 RX 330 for as long as I can remember. I have it at the Lexus dealership right now because I'm sick of this happening when it's cold outside. If it's 15 degrees outside, why would it blow cold air in the cabin? Well, Lexus told me that this is the normal operation of the heating system and there is nothing they can do to fix it. But if everyone in the car is subjected to this hot cold treatment, then this is not normal and it is a problem -- one that Lexus should/might have developed a fix for by now. One of the representatives insisted that there is a manual over-ride and it would not get cold again. All I had to do was make sure none of the green lights for the climate system are lit-up on the dash. I could adjust the Mode and Dual operation buttons but that's it. 7 minutes away from the dealership, it started blowing cold air which lasted several minutes, followed by broiling hot air, followed by luke warm air. Could anything be more maddening? They say that the car's computer is trying to maintain the 75 degree temperature I set it at but in doing so, all passengers in the car are subjected to extremes of temperature that becomes intolerable after 15 - 20 minutes in the car. The new loaner they gave me stays toasty warm at 73 degrees the whole time and everyone in the car is comfortable without screaming about the cold air blowing on their feet when it's 5 degrees outside. When I asked about the new car operation, Lexus response was there have been improvements in the heating systems over the years. So if there was not a problem to begin with, then why are improvements necessary? This could be another one of their unpublished recalls or just a poor design that they've chosen to ignore. Lexus blows.
I appreciate the comments. I had it looked at and found that there was a problem with the radiator that then put air voids in the system that messed with the heat / cold. Once replaced all is now well.
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