Ls 400 Air Conditioning (ac) Question

[jasonmckinley]

All-

I have a 1996 LS 400- let me start off by saying this is the best car I've ever owned. I have had it just over 1 year and it has about 160k miles. Runs perfectly- I have just one question. When I'm on the highway for roughly 45 minutes or more, my AC starts acting weird. The power of the fan (no matter how high I turn it) never seems to be higher than if it were on the lowest power setting. It also sounds like something is blocking the air from coming out of the vents. It only does this on longer trips; and being a sales rep, I notice this a lot. The way to get it to "fix itself" is to press the AC button (therefore turning off the AC), and hit the button that toggles between circulating the air or pulling in from the outside (I normally leave it on circulate, so toggling it for me is to put it to pulling from the outside). After about 1-2 minutes on these new settings, the air comes out at the appropriate power. Then, I push the AC button again, and hit the circulate button again, and all is back to how it should be (for another 45 minutes or so, then I repeat the sequence).

Does anyone know why this is happening? I took it to a Lexus certified mechanic and he said he wouldn't be able to diagnose it without it actually having the problem at the time of it being in the shop (and his shop is only 10 minutes away from me). They did check the system out and replaced something (AC filter maybe), and told me that eventually I'll have to get a new "blower motor" but were unaware of the problem I'm experiencing.

From what I've seen on these posts, these cars are so reliable and so similar that I'm sure someone else is having this same problem, I just can't/haven't found the thread on it.

Open to ideas; thanks.

[nc211]

when you're turning the a/c on, is the "auto" light coming on? If the auto light comes on, then what is happening that the car knows the temp inside, and is adjusting the fan speed, and sometimes the vent directions "floor, person, etc.." to keep it at the designated temp. If it's not on auto, and you're increasing the fan speed manually but nothing is happening, then I think the recir/fresh air door is getting stuck. Have you noticed any small pieces of dark grey foam coming from the vents, or on the floor? Like insulation tape type insulation. If so, a piece might be jamming the door. My 95 would spit that foam stuff every now and then at me, usually in cm pieces, but on a couple of occasions they were about an inch in length. I have no clue what it's from, but it didn't harm the operation of the system, just annoying sometimes.

the next time you hit the a/c, adjust the temp settings and see if the airflow increases.

[jasonmckinley]

i should have been more specific in the post- this is definitely not a function of the car regulating the temperature. i live in atlanta and during the summer this was happening when it was over 100 degrees outside. the car should certainly be doing everything it can to keep the inside cool (when i have it set to "cold"). so, this isn't the car realizing the inside temp and kicking down the fan speed- instead it's that the fan speed is all the way up but the amount of air coming out is equivalent to the lowest level.

also, i haven't seen any of the chunks of material coming out of the vents. any other ideas?

thanks-

[aarman4]

i should have been more specific in the post- this is definitely not a function of the car regulating the temperature. i live in atlanta and during the summer this was happening when it was over 100 degrees outside. the car should certainly be doing everything it can to keep the inside cool (when i have it set to "cold"). so, this isn't the car realizing the inside temp and kicking down the fan speed- instead it's that the fan speed is all the way up but the amount of air coming out is equivalent to the lowest level.

also, i haven't seen any of the chunks of material coming out of the vents. any other ideas?

thanks-

I am starting to wonder if your AC heat exchanger is icing up.... Turning off the AC and opening the outside air vent at 100 degrees would melt the ice very quickly... Why not leave it on outside air when running AC and see how that goes...

Good luck!

[nc211]

There is a diagnostic trick you can do with the a/c unit that will give you a readout on how the system is working. I can't recall what it is though. I think DCFish knows it though. Search under my name, and look towards the very beginning when I first came around... or better yet, let me see if I can find it....

Edit: well I can't find it. Searches only go back 1,000 posts by name. I'll PM DCFish and see if he knows what it is, and see if he will join the conversation. He knows these sort of tricks!

[dcfish]

There is a diagnostic trick you can do with the a/c unit that will give you a readout on how the system is working. I can't recall what it is though. I think DCFish knows it though. Search under my name, and look towards the very beginning when I first came around... or better yet, let me see if I can find it....

Edit: well I can't find it. Searches only go back 1,000 posts by name. I'll PM DCFish and see if he knows what it is, and see if he will join the conversation. He knows these sort of tricks!

This is for the GS but I also think it works for the LS.

GS_HEATING_AIR.pdf

AIR_COND_BULLETIN.pdf

[wwest]

All-

I have a 1996 LS 400- let me start off by saying this is the best car I've ever owned. I have had it just over 1 year and it has about 160k miles. Runs perfectly- I have just one question. When I'm on the highway for roughly 45 minutes or more, my AC starts acting weird. The power of the fan (no matter how high I turn it) never seems to be higher than if it were on the lowest power setting. It also sounds like something is blocking the air from coming out of the vents. It only does this on longer trips; and being a sales rep, I notice this a lot. The way to get it to "fix itself" is to press the AC button (therefore turning off the AC), and hit the button that toggles between circulating the air or pulling in from the outside (I normally leave it on circulate, so toggling it for me is to put it to pulling from the outside). After about 1-2 minutes on these new settings, the air comes out at the appropriate power. Then, I push the AC button again, and hit the circulate button again, and all is back to how it should be (for another 45 minutes or so, then I repeat the sequence).

Does anyone know why this is happening? I took it to a Lexus certified mechanic and he said he wouldn't be able to diagnose it without it actually having the problem at the time of it being in the shop (and his shop is only 10 minutes away from me). They did check the system out and replaced something (AC filter maybe), and told me that eventually I'll have to get a new "blower motor" but were unaware of the problem I'm experiencing.

From what I've seen on these posts, these cars are so reliable and so similar that I'm sure someone else is having this same problem, I just can't/haven't found the thread on it.

Open to ideas; thanks.

It sounds as if your evaporator is icing up/over and completely, or mostly, blocking the system airflow.

The earlier LS400's were prone to do this but mostly at high altitudes, mountain passes, etc.

If the later series, yours, still has an EPR valve, Evaporator Pressure Regulator, that would be where to look first. But it will take someone really sharp on A/C systems (not likely to be found at any dealer) to understand how that works and how to adjust it.

[jasonmckinley]

great advice from everyone who responded; thanks. i'll begin looking into these tips. if anyone else has comments, i'll take them. thanks again

[mehullica]

Sounds like the cabin filter is plugged.