Updates on the HVAC noises - any suggestions? (1 Viewer)

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dnp

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May 2, 2004
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Location
Jackson, MS
2004 GX, non-NAV. 175,000 miles.

I'm having an issue that I can't seem to figure out: Starting this last spring, whenever the HVAC is put in a/c mode, several of the actuators have begun to make noise - I mean, it's like Geppetto's workshop noises behind the dash, and it'll run you crazy! I have isolated the noises to the following 3: (a) the actuator behind the glovebox that controls the fresh/recirculating air damper, (b) the actuator below / right of the radio that controls air temp. blending, and (c) the actuator that selects HVAC mode. These things click and carry on so much that I honestly can't drive the truck until the weather turns cold (for some reason, none of the actuators make noise with the HVAC in heat mode.......!) Oh, and if I leave the mode in fresh vs recirc. air, that one will generally stay quiet.

My thinking is, the likelihood of 3 actuators going out simultaneously is highly unlikely; therefore, my thinking is that whatever module that controls the HVAC is the most likely culprit. My primary problem is: I can't seem to run down where the HVAC computer/module/whatever-it's-called is located. I presume the truck probably has some sort of stand-alone module that controls the HVAC system, but I just can't find any diagrams that lead me to it.

It's been suggested that all of the HVAC is controlled by the HVAC "head unit" in the dash, but I don't want to start replacing things like that until I'm reasonably sure that's where the control module resides.

Anyway, that's a general explanation of what's going on. Anyone have any thoughts / suggestions?

Thanks,
David
 
I have the same noises, but I have ignored them :p
 
I have the same noises, but I have ignored them :p
HA! If I could figure out how to ignore these, I would........sometimes I want to drive it into a tree, just to make them stop!!!

Has to be a fix for this, I just need to know what needs to be replaced.........
 
Search for “gx470 servo”

Mine make noise too and some people take the dashboard off and head unit to grease the gears of the servo and other components in there that have similar gears.

I can’t search now but someone posted a diagram and photos of all those gears. There’s even YouTube videos on this. I think 4Runner has the same issue.
 
Search for “gx470 servo”

Mine make noise too and some people take the dashboard off and head unit to grease the gears of the servo and other components in there that have similar gears.

I can’t search now but someone posted a diagram and photos of all those gears. There’s even YouTube videos on this. I think 4Runner has the same issue.
Thanks for the response, but I'm not sure that would be a solution to the problem I'm having. It's not that the servos make noise WHEN they move, it's the issue that they're constantly MOVING for some reason. I'm trying to locate the reason FOR their moving, and since 3 of them started their activity at the same time, I have to believe it's as a result of some issue with the module(s) that control them. The module(s) is/are what I'm seeking.
 
Mine also make noises, but only if I have the temperature set above COLD. If I have it set as cold as possible it makes no noise.

Have you done the self test?
 
Mine also make noises, but only if I have the temperature set above COLD. If I have it set as cold as possible it makes no noise.

Have you done the self test?
Actually, you know, I DID discover that last summer! If it's all the way COLD, it is less likely to make the noises........

Sooooooo, anyone know the cure? I'm not one to leave a problem unresolved. The truck will get sold before I'll "live with it."
 
I always thought it was the mixer flopping around mixing cold and hot to hit the target temp and just making a racket.
 
I've been doing a lot of research on this for our cars. People blame the air mix servo for the noise near the driver side AC vent. It's accessible via the dash/instrument cluster. I tried to get hands on but couldn't via the radio/nav.

It's actually not the gearing itself which needs to be greased but contacts somewhere on the unit. It requires the module to be carefully pried apart, contacts cleaned and regreased using dielectric grease. That should do the trick if the module hasn't cooked itself. If it has, I think a replacement is $100-200.

I dunno about the other modules behind the dash though.
 
Just got back to this thread.

Thanks to those who have responded so far. That being said, I think I may need to rephrase my initial query to: Does anyone know what controls the motion of above-referenced servos (actuators)? Mine move when I don’t want them to, and I want to make them stop.

Thanks for any help anyone can offer.
David
 
Just got back to this thread.

Thanks to those who have responded so far. That being said, I think I may need to rephrase my initial query to: Does anyone know what controls the motion of above-referenced servos (actuators)? Mine move when I don’t want them to, and I want to make them stop.

Thanks for any help anyone can offer.
David

I think the auto air climate controls the servos. To disable that would entirely disable the auto AC function and perhaps all AC function.

They're basically moving all the time because of a bad or intermittent electrical connection. From all that I've read, it goes away when the unit described above is regreased.
 
I think the auto air climate controls the servos. To disable that would entirely disable the auto AC function and perhaps all AC function.

They're basically moving all the time because of a bad or intermittent electrical connection. From all that I've read, it goes away when the unit described above is regreased.
So, since the above unit is solid state, you're saying the electrical connections need to be greased with dielectric grease?

Before I start replacing components, is it everyone's understanding that the control head (the part with the HVAC control buttons on it in a non-nav truck) IS the computer that controls HVAC function? I just want to make sure there's not some other remote ECU that moves the actuators after taking inputs from the control head.
 
I think they move all the time, not solely because of bad or intermittent electrical connections, but because it is the only way to modulate the temperature to match the desired HVAC setpoint. If the setpoint is at max cold or hot, then there is no reason to modulate the blend door, so the servo stays still and is quiet. If you have the setpoint anywhere between max cold and hot, 68° for example, then the blend door needs to open and close every so often to maintain the 68° cabin temp.

The heater core is always "on", and the blend door diverts some (or all, depending where your setpoint is) of the cold air coming out of the AC evaporator to the heater core before it comes out the dash vent. This is how you can have a different temperature on each side of the cabin. Here in Phoenix I wish I could turn off the heater core somehow because I can feel it radiating heat even when the AC is on max cold, but that is another issue.

If your servos are too loud when they move, then they may need to be cleaned and regreased, or simply replaced. It could also be that the linkage is making noise, or the pivot point of the blend door itself. If the servos are twitching randomly, then as mentioned earlier in the thread, it may be an electrical connection. Have you done the HVAC self test? It tests each blend door at each setting and can help figure out which one is noisy.

The computer that controls the HVAC function is in the "control head" as far as I know. The wiring diagram for the Prado shows it there, I have not seen the GX wiring diagram but maybe someone else can confirm the location of the HVAC ECU.
 
OK, after a lot of time now (and after actually being unable to drive this truck due to the noises - I'm afraid I'll be tempted to intentionally drive it into a tree just to get it to shut up), I've made some efforts.....but with no positive results!

Some of this may be due to my stubborn thinking: As you'll recall above, I have the three main servos that control the HVAC - the mode, servo, the temp. servo and the recirc/fresh air servo - all making constant movements / noises. When I say they're making noises, I don't mean the normal, subtle, virtually inaudible noises. I mean full-on, full range of motion, back and forth, incessant noises! As I mentioned above, it's like Gepetto's workshop! Also, these aren't squeaking, etc. noises, they're servo noises. For instance, if you had a servo that defaulted to one direction with no current, but electric current caused it to go to the full opposite direction, then mine would be like someone was turning the switch on and off at various speeds. Sometimes in quick succession, sometimes slower. (Note: All this happens ONLY when it's hot ambient temperature and the a/c function is being utilized. If the thermostat is turned to FULL HOT in the summer (even 84 on the thermostat won't work, has to be FULL hot), NO movement at all. Also, if the temp is cold outside, and the heater is used, rarely do I hear anything.)

SO, since all 3 servos are constantly moving at various speeds, my way of thinking is that there's a problem with the "controller end," not the end "being controlled." Using that logic, I replaced the a/c head unit on my truck (mine is non-nav), thinking that should cure the issue. It didn't. Then, I thought, "what about the thermistor? Maybe it's thinking it's a different temperature inside the truck than it actually is." Nope. Didn't work.

Therefore, unless I'm overlooking some other component that controls these servos, I'm back to the same point. What am I missing? It's been a couple of years now, but I don't recall it doing this before Lexus replaced my dash.....but I also don't recall it starting to do this right after they replaced it either. Could all 3 servos just "coincidentally" start making noise at the same time, in the same fashion?

I get so frustrated with it, I just let it sit during the hot months, but I'm tired of not driving it. It's one of the best trucks I've had, but I just can't drive it with those noises. I suppose I could replace each of the very expensive servos, but that just doesn't seem like the logical fix to me.

Anyone have any ideas?

Thanks,
David
 
OK, after a lot of time now (and after actually being unable to drive this truck due to the noises - I'm afraid I'll be tempted to intentionally drive it into a tree just to get it to shut up), I've made some efforts.....but with no positive results!

Some of this may be due to my stubborn thinking: As you'll recall above, I have the three main servos that control the HVAC - the mode, servo, the temp. servo and the recirc/fresh air servo - all making constant movements / noises. When I say they're making noises, I don't mean the normal, subtle, virtually inaudible noises. I mean full-on, full range of motion, back and forth, incessant noises! As I mentioned above, it's like Gepetto's workshop! Also, these aren't squeaking, etc. noises, they're servo noises. For instance, if you had a servo that defaulted to one direction with no current, but electric current caused it to go to the full opposite direction, then mine would be like someone was turning the switch on and off at various speeds. Sometimes in quick succession, sometimes slower. (Note: All this happens ONLY when it's hot ambient temperature and the a/c function is being utilized. If the thermostat is turned to FULL HOT in the summer (even 84 on the thermostat won't work, has to be FULL hot), NO movement at all. Also, if the temp is cold outside, and the heater is used, rarely do I hear anything.)

SO, since all 3 servos are constantly moving at various speeds, my way of thinking is that there's a problem with the "controller end," not the end "being controlled." Using that logic, I replaced the a/c head unit on my truck (mine is non-nav), thinking that should cure the issue. It didn't. Then, I thought, "what about the thermistor? Maybe it's thinking it's a different temperature inside the truck than it actually is." Nope. Didn't work.

Therefore, unless I'm overlooking some other component that controls these servos, I'm back to the same point. What am I missing? It's been a couple of years now, but I don't recall it doing this before Lexus replaced my dash.....but I also don't recall it starting to do this right after they replaced it either. Could all 3 servos just "coincidentally" start making noise at the same time, in the same fashion?

I get so frustrated with it, I just let it sit during the hot months, but I'm tired of not driving it. It's one of the best trucks I've had, but I just can't drive it with those noises. I suppose I could replace each of the very expensive servos, but that just doesn't seem like the logical fix to me.

Anyone have any ideas?

Thanks,
David

At some point, I would have long given up and just go to the dealer. I know that isn't a completely satisfying answer for a DIYer but taken into account the amount of time and money spent on parts, the dealer becomes the best option.
 
Yeah, I thought about it, but my experience has been that the WORST place to expect a satisfactory outcome is at a dealer! It's actually counter to reason, because you figure, if they're only focusing on one brand, they've got to be the best at it....problem is, I don't think I've ever had a car fixed at a dealer....even Lexus.
 
*Salty Warning*

I'll second David's comment here. I just purchased a GX470 from a local "Elite of Lexus 20 years in a row!" Lexus dealer, went over the whole car, went over their inspection history and the repairs they did, and even asked about the pulsing in the drivetrain. I was told during the test drive that it was the tires wearing unevenly and I didn't need to worry because their inspection is thorough and done by Lexus Certified Technicians. After replacing the tires, my mechanic found a lunched differential in about 20 minutes. The dealership will do nothing for me despite selling me a car that isn't road-worthy with a smile and a handshake. Don't expect customer service from a dealer above anything you'd get on Craigslist.

/salty/
 
Yeah, I thought about it, but my experience has been that the WORST place to expect a satisfactory outcome is at a dealer! It's actually counter to reason, because you figure, if they're only focusing on one brand, they've got to be the best at it....problem is, I don't think I've ever had a car fixed at a dealer....even Lexus.
Sorry to hear that your dealer is not worthy.

Maybe I'm lucky but I have a great local Lexus dealer.
 
Therefore, unless I'm overlooking some other component that controls these servos, I'm back to the same point. What am I missing? It's been a couple of years now, but I don't recall it doing this before Lexus replaced my dash.....but I also don't recall it starting to do this right after they replaced it either. Could all 3 servos just "coincidentally" start making noise at the same time, in the same fashion?

I get so frustrated with it, I just let it sit during the hot months, but I'm tired of not driving it. It's one of the best trucks I've had, but I just can't drive it with those noises. I suppose I could replace each of the very expensive servos, but that just doesn't seem like the logical fix to me.

Anyone have any ideas?

Has anyone checked to see if the HVAC system is throwing codes? Using Techstream, you can run a diagnostics check on the truck and one of the systems that it checks is the HVAC system. These codes won't show up on the MIL on the instrument panel, but Techstream can see them. I can't promise it would provide useful info, but I'd definitely check it if I were you.
 
*Salty Warning*

I'll second David's comment here. I just purchased a GX470 from a local "Elite of Lexus 20 years in a row!" Lexus dealer, went over the whole car, went over their inspection history and the repairs they did, and even asked about the pulsing in the drivetrain. I was told during the test drive that it was the tires wearing unevenly and I didn't need to worry because their inspection is thorough and done by Lexus Certified Technicians. After replacing the tires, my mechanic found a lunched differential in about 20 minutes. The dealership will do nothing for me despite selling me a car that isn't road-worthy with a smile and a handshake. Don't expect customer service from a dealer above anything you'd get on Craigslist.

/salty/

How long ago did you buy it? Does your state have a 'buyer's remorse' law?
 

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