Rx300 - Heat Cold Or Hot, Not Much In Between

[wofran]

The heat in my 2001 RX300 either runs hot or cold, limited in between. All the vents work, as does the fan. There is heat if the temperature is all the way up to "Hot" down to a setting of around 78 (maybe a little lower). Between Hot and 78 I can detect the temperature change. Much below that the heat cuts out and there's only cool air. Once or twice when I was raising the temperature the air was cool and then the heat just kicked in (I only tried this a few times).

Any ideas.

[Filehorse]

A roundup of the usual suspects would certainly include the Air Mix Servo. It sounds like your Air Mix Servo control has deteriorated to the point where it is all-or-nothing; i.e. Hot or Cold. Check this link for a discussion of issues and a reference to a replacement guide for the Air Mix Servo and the Mode Servo. Air Mix Servo Replacement Discussion

If you're going to replace one servo you might as well replace them both since you have to remove the Mode Servo to get to the Air Mix Servo. If your Mode Servo hasn't started 'rattling' yet, it's just a matter of time. If you don't mind standing on your head under the glove box, this is really a fairly easy DIY although getting the Air Mix Servo mounting screws out can be a bit tricky. I just did all this on my 2000 RX300 AWD about two months ago. It was time well spent. Also, the link I have referenced also had an online reference for a place to purchase both servos for a LOT less than your local Lexus Parts Department typically will sell them to you. There is a lot of information available on this and other RX forums detailing exactly how to DIY this project.

Lotsa luck.