I performed several searches, but none addressed the issue I'm having. My apologies in advance if this is a problem that's been addressed on here before. I've discussed it on IH8MUD.COM, but then I remembered this forum is more likely to understand Lexus-specific problems.

OK, here's what I've got: 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 behind the dash have begun to make noises - I mean, when it starts, it's like Geppetto's workshop behind the dash, and it's running me crazy! I have isolated the noises to what I believe are the following 3 sources: (a) the actuator below/behind the glovebox that controls the fresh/recirculating air damper, (b) the actuator below / right of the HVAC controls that controls air temperature blending, and (c) the actuator below/left of the HVAC contols 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, but as soon as a/c is called in to blend with the heat.......! I also discovered this last month that, if the a/c starts blending in, and if I put the HVAC setting on full HOT, the noises stop) Oh, and if I leave the mode in fresh vs recirc. air, that actuator will generally stay quiet.

I believe the likelihood of 3 actuators going out simultaneously is highly unlikely; therefore, my thinking is whatever module controls the HVAC is the most likely culprit. My primary problem is: I can't seem to run down where the HVAC computer/module/ECU is located. Because there are so many in other places in the truck, I'm guessing 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. That being said, it's been suggested that the HVAC "head unit" in the dash IS the HVAC ECU, so that may be the location of what I'm seeking. However, I don't want to start replacing things 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? Seriously, unless I can come up with a fix, this vehicle will remain parked until the weather turns cold next winter........and that'll be a shame, because I REALLY like driving it!

Thanks,
dnp

 

 

Yeah, these are pretty crazy. They all work, it's just that they never stop. It's the equivalent of turning a switch on and off....quickly. And it's not as if they work, but they need to be lubricated. That's what people have advised me to do over and over. It's sort of the opposite, in that they just need to stop moving altogether (except for the occasional normal adjustment.)

 

It's unusual for 3 to go out at once. But I had a college car that burned out both headlights at the exact same time and I wasted a day tracing the wiring, convinced it was the switch or a fuse... when it was the bulbs.

The actuators are stepper motors and they report their position back to the A/C ECU, so if they're reporting the "wrong" position, the ECU will command them to move to the "correct" position. I would pick the one that easiest to get to and replace it to see if that solves your problem.



(Image from Autozone repair guides)
Chip H.

 

Thanks for the response. Are you saying that one bad actuator (stepper motor) could make the others malfunction as well?

 

No - it's that you sound unsure this is the problem, and this is a way to test your hypothesis without going crazy with the credit-card. Fix one - if the sound diminishes, the others are likely bad too and you can proceed with their replacement.

Chip H.