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Lexus LS460 air conditioning acting weird

2011 LS460, 26,000 miles. About a year ago, the Lexus dealer replaced the a/c air filter (I believe it was the one behind the glove box.) Since then, the a/c has been erratic. Among the things it has done at least once include: Cold air from dash vent, hot air from bottom vent, simultaneously; blows cold air from dash vent when car starts, even when the ambient temp is cold; outside temp reads 73 degrees for hours, though actual temp was in the 60’s; noisy fan at bottom vent, but very little air; set temp ignored…
I took it to the Lexus dealer, who said they “cannot duplicate” any a/c problem. I’d heard a bad “a/c amp” can cause problems like mine, and that the amp is located in the glove box area. Dealer won’t change the amp, will do nothing unless they can duplicate the problems. By their nature, these things happen sometimes and I can’t rush to the dealer when they occur. They might be gone by the time I get there.
What do you think?

Unfortunately, you have to wait until the problem occurs often enough that the dealer can duplicate it. On the positive side, the dealer isn’t throwing parts at it to make you think they know what’s going on.

Another thing: that filter behind the glove box is the cabin air filter. It removes particles from outside air before it gets into the car. It has nothing to do with the air conditioning. The timing of the air conditioning problems and cabin air filter replacement is coincidental.

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I mis-spoke about the name of the filter, I guess. I’ve seen reports that the a/c amp is located behind the glove box, and could have been damaged when the filter was changed. Is that not true?

The dealer isn’t throwing parts at it, or doing anything, really, because they don’t dispute that the problems began immediately after the filter was changed, making it their responsibility. They are not the most honest people.

Why are you taking this out of warranty vehicle to the dealer anyway . Find a independent air conditioner shop.

What is an a/c amp? Ah, it’s an interface between the control unit and the things being controlled. There you go. Only 1 issue I have seen. So it’s very rare.

I’ve never heard of an A/C amp either. It seems to be a Toyota/Lexus thing.

The A/C amp, from what I gather (via Google), is a control module that is used to amplify weak signals from several sensors and prepare them to be used by the logic to control compressor operation. There may be an adjustment knob on this module that adjusts when the compressor clutch engages based on engine RPM. The amp is located near the blower motor and cabin filter, so it is possible this adjustment was disturbed when the filter was replaced.

My interpretation of the operation of that system is that the compressor clutch is a redundant fail safe which is not even installed on all models. The AC is totally controlled by the module through 2 solenoid controlled valves, One valve is at the evaporator and the other is in the compressor. I can’t imagine that the system can be diagnosed without the factory manual and likely a diagnostic tester dedicated to the system. Toyota seemed to be seeking perfection and perfection comes at a heavy cost.

The a/c amp on a Lexus is the electronic module that interfaces between the control center and the various components to be controlled.

I don’t understand why you’re taking it to them if you have established that they are not honest.

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A long shot… you could remove the filter temporarily and see if that makes a difference. I don’t see how it would, but doing nothing won’t help at all.

There was some sort of indication (I don’t recall what) that the air filter was due for replacement. My independent repair shop is a good distance away, the dealer wasn’t charging outrageously for the filter change, and HOW COULD THEY SCREW UP SOMETHING AS SIMPLE AS CHANGING AN AIR FILTER?

It kind of sounds like one or more of the hvac actuator motors and/or doors may be faulty

The opening in the glove box to access the cabin air filter is too small for anyone to be able to damage the A/C amplifier. I have seen a number of recirculation doors doors damaged while replacing cabin filters by shops unfamiliar with Lexus vehicles but this shouldn’t happen at a dealer and the symptoms are different.

At the same time? When in bi-level mode the panel temperature will be lower than the floor temperature, this is dome to compensate for the heat from the sun though the windows.

I live in the desert, if it is 65 F outside the cars interior will be 90 F, if I push “Auto” on the controls the system will cool the interior. If you are using the auto mode there should be a short delay in output after starting the car, if you are not using auto the system will start blowing in the direction that you last selected right away even if there is no heat available. For the ambient temperature display to update the vehicle must be moving at 35 MPH or greater for a specific amount of time.

Your complaint doesn’t have details that would suggest that there is a problem so a technician is not going to spend much time on this.

I don’t live in the desert.
The car’s interior was as cold as the outside when I started it, so it wasn’t cooling the interior. I was going 65mp on the freeway for some 15 minutes, and the cold air continued. I had to set the temp to 76 degrees before cold air stopped. For 6 years, the temp has been set for 72 degrees, without the cold air problem. This happened when I picked up the car right after they said THEY HAD CHECKED THE A/C. Coincidence? I don’t think so.
This is in addition to the a/c being wacky since immediately after the filer was replaced, and staying that way. You’re right that they’re not going to spend much time on this, they reported they checked the “doors” and they were working. That’s all they did…

Problem is pretty much consistent with what they call the “amplifier” going bad.
If so, brand new part pricey, plus, may be buried under the dashboard.
Good Luck

BTW… the filter is accessed via glove compartment.
Here: YouTube - LINK How To
Cannot picture filter change affecting air controls.

Coincidences do happen.

I brought the car back to the Lexus dealer because of the a/c problems. They gave me this report:
As I noted earlier, when I picked the car up and started home, the a/c was malfunctioning. The dealer’s customer service sent me an email asking if I was satisfied. I called and let their CS person know I wasn’t, and why, and “couldn’t duplicate” wasn’t acceptable. She had the Assistant Service Manage phone me. She sticks to that position, says changing the air filter couldn’t have caused the many a/c problems, even if they hadn’t existed prior to the change, they will check the a/c amp if I want to, at my expense. I refused. The a/c still needs to be set to 75 degrees to blow warm air, even if the ambient and interior temps are in the 60’s, which wasn’t the case before they changed the air filter. My position is that if they couldn’t duplicate the problems, they should investigate further. The ASM disagrees.

Suggestions for my next step will be appreciated.

I would agree with the shop. They investigated and it worked as designed, they were unable to duplicate the problem as you described. Don’t forget, they are in the business to do repairs and make money. I am sure they would love to find something and fix it.

I think you may miss the point that the a/c worked fine until they replaced the filter, if they find a problem they’ll have to fix it at no charge. After they supposedly checked it and “couldn’t duplicate” the problem, it was worse. When I picked the car up the outside and inside air temps were 63 degrees; the a/c was set for 75 degrees. It blew COLD air from the upper vents on the driver’s side (passenger side vents blew warm air). It still operates that way. For 6 years before they changed the filter, the a/c was set for 72 degrees and it was always comfortable.

In which case something is wrong with it, but it was likely not caused by the filter change and is coincidental.

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Some additional thoughts for the OP to consider:
He is convinced that the dealership did something wrong, and they deny it. This is a pizzing contest that is not likely to be resolved without a skilled second opinion.

If I was in the OP’s situation, I would take the car to an independent A/C specialist shop for diagnosis. After that shop comes up with their findings, then the OP should ask whether the problem could have been caused by improper replacement of the HVAC filter. If the indy A/C specialist says that this problem could have been caused by the dealership, then have the indy shop put it in writing–in detail–on their letterhead, and take that document to the owner of the dealership.

If it can be demonstrated that the dealership was at fault, they will likely reimburse the OP for the cost of the diagnosis at the indy shop, and will perform the needed repair w/o charge. Then again, this problem is likely to be nothing more than a coincidence, but without a second opinion, this is going to be a Mexican Standoff with no resolution.

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