brent0226

I don't think the GX's auto A/C system works correctly. I thought the whole purpose of having auto A/C is to set it and forget it; I find myself, however, constantly adjusting the temperature. It's always either too hot or too cold. Often times I have to bump it up to 78 degrees or so, then after a while take it way down.

Then sometimes it will just randomly start blowing cold air, then start blowing hot, and then again randomly cold air. Is there something wrong with the system?

Our other two cars with auto A/C (Jetta, F150) work just fine with the systems set at 68 and 72, respectively. You don't ever have to adjust the temperature on them.

looknow12

I've noticed that too. I think when it's really sunny out, but still cold, the direct sun light fools the system into thinking's its warmer in the car then it actually is and to compensate it blows a lot of cold air. I have not however noticed it exaggerating how much hot air to blow.

I also the have to adjust the temperature quite a bit.

jacksonian

I notice it on both extremes. If it's really cold outside, and the temp is set to 72, it will get blazing hot, pumping out hot air and won't stop. If it's really hot outside and the temp is set to 72, the A/C will freeze you out blowing ice cold air really hard. I've just decided to take it off of auto altogether I think.

degeester

Lexus issued a Technical Service Information Bulletin on Jan. 9, 2004 regarding A/C performance improvement for '03-'04 GX-470. Ask your dealer and more importantly your service writer about TSB No. AC001-04

jacksonian

Has anyone had this fixed with the TSB yet? I'm going in tomorrow with mine for the 10k service and I'm taking this thread printout with me. I'll report back either way.

brent0226

Let us know how it goes!

fj55-100

Tsb only adresses the ac blows hot out vents after sitting in traffic in an area that is over 100% outside temp. aka/ arizona/palm spings / Issue is still pending tsb was only 10% effective

looknow12

The A/C issue is still a major problem. We are constantly adjusting the temperature in the car up and down.

I remember seeing an Ad for a Jeep Grand Cherokee several years ago where they advertised the fact that their climate control system actually detects the temperature of the passengers using infared and adjusts based on that. I know the technology exists because I have seen HVAC personnel troubleshoot commercial systems using this little handheld device. They can instantly detect the temperature of a ceiling vent without getting on a ladder. It was pretty cool.

I'm pretty confident Lexus is not doing this. But think about it, the climate control settings in the vehicle are all relative to the comfort level of the body, not the outdoor temperature. Even indoor tmp is a stretch because of direct sunlight, etc. Any other method for calculating how to stablize the temperature will not work in all conditions.

brent0226

I don't think it needs anything fancy. Both our F150 and Jetta work perfectly in keeping the cabin comfortable. I know the Jetta has a tiny fan that draws in air from the cabin to measure the temperature, and it does an almost perfect job of keeping it comfortable without ever having to adjust the temp.

dfeldmanmt

We took delivery of an '04 model GX at end Feb, and the A/C problem gives me fits. The sudden mode shift to "lotsa cold air" is caused by the sunlight detector, it is overriding the cabin air temp sensor. The real problem is poorly designed contorl system logic, the control loop gets into a saturated mode at max cold and it cannot get out until you crank up the temp to 78. The computer tech at Lexus Bellevue (WA) says he can turn down the temp-error sensitivity which may help. For next visit.

I operate the HVAC in manual mode: direct and floor air-flow, fan at 2, then control with temp changes between 73 and 76. This stops the full cold assault and has enough juice to keep up with most ambient temp changes. Have to adjust the flow control vanes on the dash sometimes.

Pretty sad performance from such a well designed/human-engineered $50K product. People have been building control systems since WWII.


DON