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Lexus GX470 blowing warm air always

ActiveEd on Thu June 05, 2014 7:15 PM User is offline

Year: 2004
Make: Lexus
Model: GX470
Engine Size: 4.7
Refrigerant Type: R-134a
Ambient Temp: 95
Pressure Low: 42
Pressure High: 240
Country of Origin: United States

I recently got this 2004 Lexus GX470 with 140k miles. Now that it's getting up to around 110 here in Phoenix I've noticed that the air conditioning is not working very well, blowing only 60-65 degree air while driving and up to 75-80 when stopped at a light. I've tried a couple things so far but am still stumped.

First thing I did was rebuilt the fan clutch with new fluid, still blowing warm air at idle. I hosed out the condenser while the fan was out. The electric condenser fan seems to be working fine, it kicks on full speed when high side gets to 225.

I ran the self test on the ac display and it showed a problem with the driver side solar sensor and a stuck recirculation damper, so I fixed the damper, but in either fresh or recirculate it is still blowing low 60s while driving. I haven't figured out how to get to the solar sensor yet.

While I had the gauges hooked up I sprayed the condenser with a hose and the high side went down but not very quickly. After spraying the condenser, pressures were 35 / 160, vent temp dropped to 61. The sight glass is mostly clear, a little foam every so often. The weird thing is it seems to foam up when I spray the condenser, and I think normally that should clear it, right? Every so often the sight glass goes black for a couple seconds.

This morning when it was only around 80-85 degrees outside when I first started the car and backed it out the driveway, the vent temp went down to 48.

Any comments or suggestions would be greatly appreciated, let me know if you need more info. Thanks!

webbch on Thu June 05, 2014 8:58 PM User is offlineView users profile

In the info, you mention 95 ambient, but in the description, you mention 110 with associated vent temps of 60-65 and 75-80. What was the ambient at the given vent temps? If the ambient was 110, then low 60's on a 110 degree day is pushing a 50 degree temperature reduction. You can't ask for much better. It does sound like you might have a very minor airflow problem, but hard to tell - at idle, you're still getting 35 deg cooler air from the a/c. There may not be anything "wrong" with the system - you're just maxing it out on such a hot day.

mk378 on Fri June 06, 2014 9:53 AM User is offline

I'd be thinking reheating from the heater not cutting off fully, or maybe just slightly low on charge-- weigh in a proper charge to eliminate that as a possibilty. Are those pressures at idle or with the engine revved up to about 1500?

ActiveEd on Fri June 06, 2014 10:00 AM User is offline

It was 95 ambient when I had the gauges hooked up, vent temp at that time was 66. It was 110 later in the afternoon when I was driving around and the vent temps were in the 60s. I agree that a 50 degree temperature reduction sounds pretty good on paper, but it still isn't comfortable. But you're right it could be that the system is not well designed for this climate. There was a TSB re. "low cooling when driving in high temperature areas", not sure what gets replaced but mine is out of warranty and apparently it's a $2000+ job.

I ran the self test again, but this time in bright sunlight and everything checked out ok. So the solar sensor is not an issue.

I'm going to check if the blend door is working properly even though no codes came up.

I might replace the fan clutch with a new OEM unit but I still don't believe it's the main problem, since the vent temps remained high even while hosing off the condenser. It should help stop the temp rise at traffic lights though.

ActiveEd on Fri June 06, 2014 10:07 AM User is offline

mk378 -- Those pressures were with the engine at 1500. Also, I just realized that the gauges are probably not super accurate since they're the autozone rental.

Dougflas on Fri June 06, 2014 1:25 PM User is offline

don't forget to clamp off the heater hoses to eliminate a reheat problem as MK suggested.

ActiveEd on Fri June 06, 2014 5:13 PM User is offline

Thank you all for your help. I took a look at it again this morning, it started out like this:

Ambient Temp: 90
Static pressure (A/C off overnight): 150
Pressure Low: 37
Pressure High: 260
RPM: 1500
Blower on high front and rear, recirculate, windows open
Vent: 63

These readings are from the autozone rental gauges and they showed low = 57, high = 67 when they were not connected to anything and both valves were opened to equalize pressure. Not the best tools.

I found a copy of the service manual and it has a section on A/C. Of course it is best to charge by weight, but the manual also shows to charge until the sight glass clears then add 100g refrigerant. I added 25g to clear the sight glass, but it foamed up again about 30 seconds later. I added another 20g to clear it again, and it stayed clear. I did not see any of the black that I saw the other day. I added another 100g refrigerant after the sight glass cleared. After that the pressures were:

Ambient Temp: 90
Pressure Low: 34
Pressure High: 230
Vent: 55

After driving around for a while it seems to be working much better than before. It was 105 around noon and the vent temps while moving were 48-55. While stopped they did creep up a couple degrees if the blower was on high, but only noticeable on the thermometer. After leaving it parked at the grocery store for 30 minutes or so, I started it up and turned the A/C on and it cooled down to 60 while parked. Yesterday when I tried that it only went to 80.

So it appears to have been low by 145g (5.1 oz) or so. Also, I added fixing the recirculation damper made a big difference. I did not check the heater blend door, since it seems to be cooling ok now.

Before I say I am done, does it seem like it is working as well as could be expected, or is there something else I should do? Thanks again.

mk378 on Fri June 06, 2014 6:09 PM User is offline

Those gauges seem to be broken and shouldn't be trusted for anything. If you disconnect the red and blue hoses from the manifold to vent all pressure out (not connected to a car of course), the gauge should read zero. *If it is close to zero, most have a calibration feature. Take the plastic cover off and turn the calibration screw on the face of the dial.

Edited: Fri June 06, 2014 at 6:11 PM by mk378

ActiveEd on Fri June 06, 2014 7:49 PM User is offline

Oh man, you're right, I explained that really badly. If the gauges were like how I described they would definitely be broken and not just crappy. What really happened was, yesterday after I was done checking the pressures I swept the refrigerant back into the system and then left the remaining refrigerant in the gauges with all the hoses still connected so I wouldn't have to purge the hoses again later. Today when I went to look at the gauges, I opened both valves to equalize the pressure and check if the gauges were reading the same, the hoses were still connected so no pressure was vented out.

wptski on Fri June 06, 2014 10:04 PM User is offline

I have a two brand new Yellow Jacket Series 41 manifold gauge sets with +/- 1% gauges and the high and low don't agree in the same manner but maybe not as much as your seeing. Many gauges are most accurate in the mid-scale area. Some are called 3-2-3 gauges which means +/- 3% in the first third, +/- 2% in the second third and +/- 3% on the last third of the scale. You figure 2% or 3% of full scale is a large amount.

Edited: Sat June 07, 2014 at 8:42 AM by wptski

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