Nauticalx

I've always wondered how the rear AC system in the UL's works. It appears that the unit can cool without the need for the compressor (in the engine compartment) to turn. Does the rear AC have its own freon and compressor? I doubt it does but then, how does it cool???

sojah

iTrader: (1)

the rear ac actually has its own ac box type thing in the trunk separate from the other ac. not sure if this is just for the air purification thing that it claims or what. i know that my rear ac as well as rear seat ac seats work much better than my main ac and front seat ac cooler things.

Nauticalx

Yeah, it works great, which makes me wonder why we dont hear a compressor running there.

jayclapp

The single compressor in the engine bay has the capacity to supply freon to both the front and rear cooler units. The engine drives it of course.

sojah

iTrader: (1)

so why is my rear so much colder than my front??

jayclapp

First, it must be remembered that the Ultra Luxury was designed primarily to pamper the rear seat passengers. The rear window shade raises automatically to provide shade (while it can be lowered and raised by the driver, it cannot be disengaged). Side window shades provide privacy and shade from the sun. Reclining seats with memory and return when the rear door is opened, massage, an adjacent refrigerator, controls for the Levinson sound system, seat temperature controls, and swivel reading lights are included. Then there is the separate air conditioner with UV filter and climate controls for the rear passengers.

The rear seating compartment is subjected to various heat input. When the shades are down, the heat input is maximized. When the shades are up, the heat input is minimized. This is a greater variation than what the driver is subjected to as he has no shades available.

Consequently there are two nearly separate air conditions systems in the UL. There is one compressor in the engine bay with valves for freon lines that run to and from the rear passenger A/C. The compressor is controlled solely by the driver. While the rear passengers are pampered, the driver is the captain of the ship. While there are three temperature controls there are only two thermostats. The two thermostats for the driver and passenger provide separate temperature control. The rear passenger control is linked to the drivers thermostat. A change in one always changes the other, whether instigated by the driver of the rear passengers.

The front A/C system has 5 blower speeds while the rear system has two. The front climate control allows the driver to turn the rear A/C on and off and choose between manual or auto operation. When A/C is selected it opens the valves that provide freon to the rear system. The compressor must be running for A/C for the rear. The rear passengers cannot turn on the compressor. That can only be done by the driver.

But the rear climate can be changed by the passengers. Choosing manual they are provided with two blower speeds controlling the airflow from the overhead vents. They can also turn the A/C off while the driver maintains his A/C. However, the air provided to the rear by the vents in the back of the driver armrest is part of the drivers system. The rear passengers have no control on temperature of this air. They can regulate the amount of airflow by partially or completely closing these vents.

Strangely, the rear passengers have inadvertent control of the front passengers temperature control when the drive and front passenger are in dual mode. When the rear passenger control is changed, the driver temperature control is also changed as they are always linked. In this case the front passenger control will go up or down by the amount as the rear passenger change.

The rear A/C has its own filter with UV for deodorizing and purifying the air. There are also two very small inlet filter on each side of the car. They probably don't do much being about 1" x 2", but they are cute as a button. They can be washed and reused.

There are a number of temperature sensors throughout the car, and I have no idea where or how many. Also, the center front vents have moving vanes that are programmed as a function of the dual zone being selected, whether there is a passenger in the right seat, and the ambient temperature. Needless to say this is a marvelous, complicated system that allows every passenger to seek and set his own environment. Now if we could only get all the occupants to learn how to use this wonderful system. Or they could just sit there and enjoy the comfort.

Nauticalx

WOW! Amazing write-up with extensive detail. Thanks. I take it you're a Lexus tech to know so much about this system?

I6turbo

iTrader: (1)

That's why I always handcuff and ankle-chain my rear seat passengers -- so they can't mess wif da climate control.

pacinitaly

I have an 03.
The rear A/C SUCKS.
Never cold, any adjustments do nothing.
I know, I know... problems,,,,, the F'in stealer ( 2 of them ) said it's fine
F them 2
I have had issues with this car since jump.... I made a mistake
Many other people that have this car ( 3 that I know of ) have no problems.

My car was built on a friday night or monday morning.
You don't have to tell me I'm just complaining, I know I am.

I love alot about the car but $35k was not worth it

thanks for listening.
Hope you and your family are well.

jayclapp

No, I'm actually a retired Aerospace Engineer. I always find out how much I actually know about a subject when I have to put it in black and white. I started writing my response and realized I was guessing about some of the operational features. I had to go to the car and run through the various sequences to determine them. I admit that I didn't actually understand all the interconnections on the three controls when I started.

That's what so amazing about this car. I find that I still find new features after all these years. In defense, the owners manual is so big that you can't expect someone to sit down, read it, and remember all the technical detail.

NC244GLT

I was searching for info on this and found this post through a google search, which is odd because I just asked a very similar question in another post..lol. I was explaining that the rear controls CAN be made to control the temp for the rear with out affecting the front settings. I test drove a UL that was setup like this, so I know it can be done, but i have no idea how to do it...and neither did my dealer. I did see a few other ULs including the one I just purchased that were linked to the front controls as you stated.

gpb

There are more than a few things that the dealer doesn't know about these cars when they are asked...