wankun

Hello CL members,

I recently acquired a 2004 GX470 with 155k miles on it. I'm in the process of performing basic maintenance to get it up-to-date. I am learning useful information from this forum and would like to thank members who contributed.

I just found out that my rear A/C is blowing warm air, while my front A/C works flawlessly. It is getting pretty hot outside and I would like to keep my passengers in the rear seats happy . I did some basic diagnosis, and here are some conditions:
1) Outside temperature: 95 deg F
2) R-134a pressure @ low pressure service port: 45 psi (according to the cheap gauge from AutoZone). Does this ensure sufficient level of refrigerant?
3) The sight glass near high pressure service port DOES show minimal bubbles
4) Compressor clutch engages, but seems to go on and off rather often (not sure if normal)
5) Condenser fan never operates, but will come on if 12V power is hooked up directly to the fan motor. Service manual says when the high side pressure exceeds ~220 psi, the condenser fan will turn on. Does this mean my refrigerant level is low and is causing insufficient pressure on the high side?
6) A/C light stays on solid, and front A/C functions as normal. However, when entering diagnosis mode (AUTO + Re-circ while turning key), the NAV screen shows Codes 21 and 24. This was done at night so Code 21 is irrelevant (solar sensor not getting light). One of the stickies revealed that A/C Code 24 indicates a faulty A/C Magnetic Clutch Relay. If it's bad then why does my front A/C operates?
7) As far as I know, the rear evaporator TSB has not been performed on this vehicle.

I am not sure what my next step should be. If you have any idea of what may cause inoperative rear A/C, please guide me to the right directions. Thank you in advance!

chiph9

I don't know if the front & rear AC units are on different refrigerant loops - they may share one.

To get the "possibly dumb" stuff out of the way - on the back of the center console, the "Rear Cooling" switch is depressed, and the fan speed is set to high or auto, and the temperature control is set to cool? And you're feeling a breeze from the roof-mounted vents?

Also - there's no filter on the back intake. It's right by the cargo area. Does it look like it might have sucked in some junk that would block the fins on the cooling unit?

Chip H.

wankun

Thanks for the reply, Chip. I think both front and rear A/C units share one same refrigerant loop.

I tried different combinations of the rear A/C controls. Fan hi/low, Temp cold/hot, etc. Each setting all yielded the same results: lukewarm air blowing from the roof-mounted vents.

I also just went to look at the air intake in the rear, and it doesn't look like anything got sucked in the block the air path.

chiph9

I think it's time you got a pro to look at the system then. Ask them to check refrigerant levels, pressures, etc.

Chip H.

chitown40

I have the same issue. According to my trusty Lexus service advisor, it is most likely a bad rear evaporator or rear expansion valve. I think it isn't too bad to replace, just have to remove a lot of plastic and evacuate / recharge the system.

BradTank

I had basically the same thing happen, and it turned out it was low on refrigerant.
The rear started to get lukewarm.

I believe it's a "known" issue on these cars where the rear evaporator has a slow leak. The dealer I took it to said it wasn't worth addressing such a slow leak and advised that I simply top off when needed. I think you're looking at thousands of dollars. They couldn't find the leak with dye, so even then, they were just assuming it was the rear evaporator since that was the area they couldn't inspect and it would be a guess to dig it out.

So once every 2 years or so, I put a can of R-134 in myself and it blows ice cubes.

sheikhmax

In my 08 Rear Cooling only activates when DUAL is tapped on the Climate Control Screen. If DUAL is not Tapped then you would not get COLD Air in the Rear... But FAN ONLY. Might be the issue....

wankun

Update

I decided to have the refrigerant evacuated and recharged. This solves all the issue including the code 24. Both front and rear A/C is are ice cold now. Thanks everyone!

freddiekd

I'm guessing you probably have a slow leak. I had a leak in the worse place. Front evaporator. Tried recharging but leak got worse as weeks passed so I changed the evaporator and all is well. Hope your leak , if you have one, is not in the front evaporator. Good luck.