I would appreciate help. I have a 99 RX300(158,000 miles). The heater blows cold air. The problem comes and goes. The controls direct the air flow properly i.e. upper/lower/defrost. However, the air is cold in all settings. Changing the temperature has no effect. When it is working, I only get hot air when the temperature is at a setting of 87 or above.

A little background: I hear the noise coming from the glove box area which I have read about in the forum. Irritating, but I had heat (at least on occasion). Yesterday the heat was working properly. This morning after about 10 minutes of driving, I began to hear noises that I had not heard before. As best as I can describe the noise; it sounded like a pack of very miniature firecrackers going off in the heater box. It did not sound like an electrical popping and cracking. More of a mechanical popping and crackling sound. I pulled over and listened, then cycled the heat/air controls. The noise continued. I turned the vehicle off for a few seconds and then restarted the engine. This noise stopped. (The original irritating noise which I have had for some time was still there). I now have NO heat. The popping and cracking noise has not returned, but, after driving 50 miles or so, I still have no heat.

I have read many of the posts, yet I'm still confused as to which servo regulates the heat. Is it the bottom servo, or, is it the one that you have to use a short Phillips screwdriver to get around the two aluminum tubes? How can I isolate/identify the problem?

I am showing codes: 21 - 31 and 41. I have no idea what they mean (yet).

I really appreciate any help that you can offer.

 

did you find your problem? what was it?

 

I had the exact same problem and the same codes. It was the Air Mix servo that was not moving. This is the hard to reach one on the sidewall behind the Mode Servo. I have temporarily stuck it to Full Heat so I can open the window during the day and use the heater in the morning/night. I havent figured out how to reach the screw between the 2 pipes to unscrew the servo yet

 

Yup, it sounds like the air-mix servo.

 

Instructions on how to take off and reinstall the mode servo and the air-mix servo on the sticky! RX300 known to have this problem, I just removed both of mine clean and reinstall it, so far so good! if it making noise again I will have to replace it. Just take you time to disables those parts, if need take some pics of inside of servos and the moving arms, because if you don't put it back correctly it will not work! talking from experience I have to uninstall and install it 2x before it works properly. oh well it a part of learning DIY!