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Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
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I'm having an A/C issue with a 2006 GX 470 on our dealership

Customer Question

I'm having an A/C issue with a 2006 GX 470 on our dealership lot. While the AC seems to for the most part be functioning correctly, we're having a consistent noise from the dash. A breathing sound. Been described as sounding like a dinosaur or darth vader. A breathing out noise every 5 seconds or so with the AC on. Sound does not change by blower speed and immediately goes away if compressor turned off. Makes no difference which setting you have air on or which vents you have turned on. Is definitely a pressure type noise.
Suspect either faulty expansion valve or compressor although neither seems to be a common issue. Watching site glass on AC, cycles between clear and very cloudy at the same interval as the breathing sound. Also found compressor cycling consistently, on and off every couple of seconds. Matches interval of breathing noise. High and low side pressures go up and down with noise and compressor cycling. High side from around 160 to 200 and low side from around 10-30. Temp is approximately 90 outside.
Also hear a little rattle from compressor or clutch every time cycles off and back on. I wonder if the compressor cycling is what is causing my issue because I feel if it stayed on, this noise would normalize and go away but the constant cycling is what is causing it to keep coming back. I read thought that this constant cycling might be normal operation? If so, that is not my issue, but something is. If this is not normal operation, I wonder if a pressure switch may be faulty, or if there truly is a blockage in the expansion valve which might be causing the pressures to fluctuate to the point where a pressure switch is cutting the compressor off.....or something else possible. Charge amount is correct at about 1.6 pounds. Thank you for your assistance.
Submitted: 3 months ago.
Category: Lexus
Expert:  Toyota Service replied 3 months ago.

Hello. Welcome to Just Answer. Please allow me to assist you. This really sounds like the system is low on refrigerant. You should never see bubbles in the sight glass. You may have this: You might have the correct amount of R-134, but it was not evacuated properly or somebody added R-134 for no reason. This throws your pressures way off because you have air in the system plus the R-134. I would recommend you evacuate the system and then recharge it with the exact amount of R-134. Then retest the system. Also, check to see that the temperature at the center dash vent, with the AC on, re circulation on, and the blower at mid-high speed, does nto go below 34 degrees at 1500 rpm. If so, the thermister in the AC box under the dash is faulty or has debris on it. Note: use nothing in this system BUT R-134. There are other products that are alleged to 'replace' r-134, use nothing but R-134

Expert:  Toyota Service replied 3 months ago.

If you have any questions, please feel free to reply.

Customer: replied 3 months ago.
Thank you for your response. I agree that the cloudiness is not correct. When I first evacuated the system (Bosch Machine), it stated I had removed 1.4lbs. Being as this is below the minimum, I felt it might simply be an undercharged condition. I recharged though to 1.6 with the same machine and the issue did not change at all. It is possible though that the machine is not registering the refrigerant charged amount correctly. At this point the system is evacuated again in preparation for possible repair work.
Expert:  Toyota Service replied 2 months ago.

Look to see if this vehicle has a cabin air filter behind the glove box; see if it is blocked up.

Customer: replied 2 months ago.
I've checked the cabin filter and while slightly dirty, it was not clogged enough where it would restrict airflow. At this point the system is still evacuated. It held vacuum fine.
Expert:  Toyota Service replied 2 months ago.

recharge the system, by adding the proper amount of refrigerant by weight, not by volume.

Customer: replied 2 months ago.
Can you explain to me the difference between charging by weight instead of volume? Thank you,
Customer: replied 2 months ago.
Can you also confirm for me that it is normal for the compressor to keep cycling on and off every couple of seconds as I mentioned it was doing?
Expert:  Toyota Service replied 2 months ago.

The compressor cycling on and off every few seconds is usually either a too low state of charge, or a too high state of charge. A malfunctioning (internally sticking) expansion valve will also cause this. Internal sticking of the expansion valve would also cause an audible noise as the refrigerant passes thru it. If this vehicle has ever had a compressor failure, I would recommend replacement for the expansion valve and the receiver dryer.

Adding refrigerant by weight is much more exact and is the preferred way of recharging AC systems. Ambient temperatures vary, and this causes the bubbles to disappear with less than an optimal charge. Back in the days of R12 the bubble disappearing was a rather close indication of a good charge, but, R-134 is not as forgiving. When the system calls for x amount of ounces of refrigerant, that is what is optimal. More than optimal trips the high pressure switch, and less than optimal can trip the low pressure switch. Either of these trip conditions are safety features to protect the compressor. Thinking over the issue, if the proper charge does not eliminate the issue, I would, again, recommend replacement of the expansion valve and the receiver dryer. A good AC flush (with a machine designed for this) before these parts are replaced would be strongly recommended.

Expert:  Toyota Service replied 2 months ago.

Omitted this: When the low or high pressure switches trip, the compressor clutch is dis-engaged.

Customer: replied 2 months ago.
I have a feeling that is what is happening is that the expansion valve is clogged and causing the switches to trip. Watching the pressures when it was cycling, the high side was making wide sweeps. Will start there. Thank you,
Expert:  Toyota Service replied 2 months ago.

You are very welcome. I do believe it is more of an expansion valve issue than anything else. Just remember to get the system flushed first to remove any metal particles (which are probably the root cause of the valve issue).

Expert:  Toyota Service replied 2 months ago.

If you have any other questions, please feel free to reply; I will be very glad to help you further.

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