BradTank

The rear roof vents on my wife's GX470 only blows (non-cold) air, even though the rear controls are set for the coldest setting and the front is blowing ice cold. There are no error messages.

It's clear the rear is not working properly, yet there are no error messages. I searched around and didn't find an answer.

Any ideas?

thanks for the help.

mann777

Since no ECM fault is recorded as you have mentioned.
There could be many areas to look into.
1. If the Volume of the refrigerant is low
2. Check the Drive Belt tension
let us know

BradTank

Could low refrigerant make the system ice cold in the front but not cold in the rear? I just assumed it was all tied into the same system.

Maybe a vent flap that's not opening/closing?

mann777

No Both the Front and Rear Unit are induvidual Functions having seperate unit by itself, They have no relation to the unit in the Front.
If you are good at Auto electricals then suggest check the Blower Resister Transistor Assy which is within the Cooler Air Duct and the Cooler Thermistor, whcih is located behind the Evap unit.
Otherwise the best option is a specialist in AC ( Private Mechanic)
The dealer can rip you for this job, as it is a long job.

mbenz80

These are the steps to take when your compressor is not working, making noise or not turning ON. Usually bad A/C clutch relay; if there is enough (at least 35psi) refrigerant in the system.

mbenz80

Mann777, I'm very sorry to say that you are misleading this guy again.
First, the front and rear A/C is one closed system with one compressor, one condenser ( with more refrigerant in it, two evaporators, two fans and two separate controls).
If the blower resistor or transistor is bad, it would not blow at all (even warm air would not come out of rear vents).

I'm not sure what yaer is your vehicle but many 2004 models had rear A/C problem and it was required to replace the rear expansion valve. There would be snapping or popping noice coming from the rear unit. I'm not positive but I believe there is a TSB in Alldata about rear blowing only warm air out.
Some vehicles had leaking rear evaporators ( as on mine replaced on 04/15/2003 at 278 miles) but you would be loosing freon and whole A/C system would be inoperative.
Did you check the A/C system fault codes?
If you press and hold AUTO BUTTON and AIR INTAKE CONTROL BUTTON simultaneously while turning on the key to second position (before activating starter) your A/C display should come up with certain fault codes to help you pin point your problem. Bad relay will not display any code.
Post them later and I will check the service manual.
Good luck!

mann777

Mbenz
First you Quote about a solution when it is not related to the problem at all. And you mention the above steps which I have quoted is for compressor making noise. I do not know where did you learn or even get this information. The Compressor is located in the front. The so called noise which you have been quoting about AC Noise for the 2004 models TSB AC001-005 is for the crackling and static noise from the Rear AC Unit.
Next you talk about A/C Clutch relay, if there is Clutch relay issue, the A/C light would blink. And this would affect the complete AC cooling for the front and rear. Here Brad says only the rear unit is blowing warm air.
Now I still standby what I have to say Two Different Units ( in terms of functioning independently) . Yes One Compressor ( I never said two)
Now coming to the Blower Resistor Transistor, and the cooler Thermistor is to be checked, in terms of measuring voltage between the terminals, off course Brad would not be able to do that, suggested to go to a Private AC specialist. Nobody says they are bad.
To my knowledge I have not seen Lexus issuing a TSB for Rear AC blowing Warm Air. I have access to the entire Lexus Database for TSBs , Unless you say, Please post one, I would like to see that.

Please get your facts rite before you even quote that I am misleading.

mbenz80

First, I didn't even try to make you mad, sorry again and I know your knowledge helped and will help sooner or later all of us including myself here on this forum.
But, if the front is blowing ice cold, for me it would mean correct compressor operation with good belt tension and sufficient refrigerant level / volume.
Blower transistor will effect the volume of the air comming out of rear vents.
Thermistor for sure will have effect on air temperature.
Also there is an A/C relay in the rear unit, part number 88630-16090 (here at work, I only have parts list on hand), can you please check what it does?
My only information database is the service manual and my local library (public access to Alldata bases).
Thank you.

BradTank

Since the units are indeed tied to the same system, it doesn't seem likely it's a compressor or refrigerant issue. I'm guessing low refrigerant would mean lukewarm air throughout, not just the rear.

Could a blend door be stuck? Is it electrical or vacuum operated? the volume of air coming out the vents has plenty of force and all the units lights work.

Is the rear expansion valve a pain to get to?

Thanks for the help

mann777

Mbenz You quote Magnetic Clutch Relay for the rear,in one post and then you say Rear AC Relay
Quote
These are the steps to take when your compressor is not working, making noise or not turning ON. Usually bad A/C clutch relay; if there is enough (at least 35psi) refrigerant in the system.

Firstly Magnetic Clutch Relay is in the front Junction Relay Box has got nothing to do with the Compressor being Inoperative. It funtions for both Front and Rear AC as well.
If the Magnetic Clutch Relay is Faulty the compressor will still work. If the Compressor is Faulty ( MIL Warning would come up) then the Blowers with Fan will continue to work but Cooling Thermistors connected to the Expansion Valve do not. As the ECM will cut off the functioning of the AC Liquid tube pipe flow connecting from the condensor to the rear unit . The Blower continues to work blowing warm air.
ECM contols the AC Cooler Relay functionality If this at fault, the ECM would signal on the cluster with a MIL. And here it is not, There are possibilitiies the pipe getting clogged. The ECM will not detect this part. Only a physical inspection would suffice the job. And the dealer or a specialist could do the flushing of the Foreign debris clogging the Rear AC pipe.

ALAN553

I have noticed especially after the car has been sitting in the sun, it takes quite some time for the rear air to come out cool... Not sure what that path of the ductwork is but if it is running up towards the roof, the duct work may be so hot it is warming the air as it passes along for a while???

mbenz80

I have never mentioned "magnetic clutch relay for the rear" but "Rear Relay A/C" right next to rear blower and evaporator., please check the rear A/C unit parts schematic.
Now you hit the nail "clogged orifice in rear expansion valve" this very much could be it!
Rear evaporator would be warm on feel if there is no refrigerant flow through it.
Unless (but I could not find it) there is a electromagnetic solenoid valve to stop the refrigerant flow to rear evaporator that is stuck in closed position.
There is also 30A fuse #12 marked RR A/C rear air conditioning system in the engine compartment fuse box.
Would you know what that relay #7 does or what it is connected to?

BradTank

I did some searching around on Google, and it looks like there's a TSB for the rear expansion valve


My guess is it has something to do with that

mbenz80

"Firstly Magnetic Clutch Relay is in the front Junction Relay Box has got nothing to do with the Compressor being Inoperative."
So how do you activate the compressor? I thought the A/C controls turn on this relay that activates the electromagnetic cluch of compressor to engages shaft and pulley and makes it operative.
I just replaced this magnetic clutch relay last week on my own car since my compressor was inoperative (not turning ON) with A/C button flashing. I still had the original 90987-02022 that should be replaced and updated with new 90987-02028 relay.

BradTank

UPDATE

I went to the Lexus dealership (against my better judgement, I normally take my car to a good independent shop, but wife insisted her car be taken there) and they said the refrigerant was indeed low. They put dye in, and couldn't find the leak, but charged be $250 to top off the system. I could have done that with an $8 can of R-134 in 10 minutes, but I digress.

Any idea where they commonly leak? My fear is it's in the evaporator area and they'll have to dig the dash out.

If the AC goes back to blowing warm in a short period of time, believe me, I'll be raising hell about exactly what I paid $250 for.