"Auto" climate control - hearing a 'thump' from inside heater box...

[LINUS]

So as title stated, I've got a interesting thing going on in the heater box of my 40th ann 80 with the same 'auto' climate controls as a LX450, some others -

When you slide the temp bar down below say 2/3 mark from dead hot, you get a rhythmic 'thumping' sound (diverter flap I'm guessing), like it is traveling too far, then releasing. ????

Anybody been here before me & figured out a fix - having A/C would be nice without a competing 'drum track' to the radio.....

Anybody?

 

[mod5csi]

It's a continuous thumping? Change with fan speed?

I think you're on the right track with one of the flaps. Maybe you can isolate which flap? Take as much 'Auto' out of the system as possible. Then try every vent position, fan speed, AC on/off, recirculate on/off, and different repeatable positions on the slider.

I just downloaded a 97 LX FSM, goes into detail on the Climate Control, but I haven't had a chance to organize it. PM me and I can email you the climate control section, if you don't already have it.

I enjoy my Auto Climate Control, so call me an interested party on this.

 

[LINUS]

I have hard copies of my '97 LC FSM & EWD - But yeah, might be something ommitted in the FSM.

I'll play with it & post back the exact scenarios that create it - funny, my old LX450 I wasn't a fan since my intro was the basic HVAC of the plain jane '97 LC, but really I only used it to do trails, my black LC is my streeter (or was till new 40th)

Thanks - I'll get real details, but yes, really sounds like a flap hanging & recoiling making the 'thump' sound - so far same rate & fairly consistant it starts at the 2/3 hot position, and anything 'cooler'/further left.

 

[SUMMIT CRUISERS]

Subscribed… My 40th has the same issue. Haven't dug too deeply into it yet. Definitely sounds like a solenoid valve trying to repeatedly open a stuck flapper door. Since it does it only when the temperature lever is moved cooler, it might be a solenoid valve trying to move a stuck heater control valve cable. To operate the AC in the coolest setting, I unhooked the cable on the heater control valve and manually closed it.

 

[thatcabledude]

I had the same sound with my Limited 4Runner when selecting a lower temp... The little motor/gear that moved the heater valve had the gears on it strip. When to changed to a lower temp the motor make a continuous thumping sound. The gear only moved about a quarter turn the valve's full range of motion. I was able to take the motor apart and flip the gear to a not stripped area.

After a year or so it happened again. This time I realized the gear was damaged because the cable to the heater valve was stiff to slide. I lubed the cable and got a new motor from Beno and all was good.

Maybe this is the same issue for you guys as well. The 4Runner was a 2001 with auto climate so maybe it used a similar design.

 

[LINUS]

@thatcabledude - I'm betting HUGE that's what it is, the sound isn't rapid enough to be say fan blades (bet we have 'squirrel cage' type anyhow) - but yes, to the idea of a stripped gear, catch-n-fail type thing.

Super helpful & betting you called it, once I finish work & get a chance I'll post back my real world combos of what triggers it & such.

Just out of curiousity, what kind of work was it going in there - was the motor/gear in the HVAC box inside the dash, or were you working from the firewall side as well?

My 40th has 360K on it and I plan a coolant flush soon, so a new heater valve may be part of my parts update to the heater (rear heat already bypassed by PO).

 

[thatcabledude]

The little motor I'm referring to was inside the truck under the glove box area.

 

[thatcabledude]

This is what the servo motor looks like and its location on a 3rd gen 4Runner:

Maybe it's similar on the 80. Get it to start clicking and then start poking around listening and feeling with your hand. If it ends up being the same thing you'll be able to feel it clicking.

 

[LINUS]

Hey all -

I been working days & splitting wood eves, so hadn't had a chance to update yet - I'll edit this post (or add a new if Mudders make new posts) - this is still a live issue in my 40th, and I have a pet peeve of questions asked / solutions not updated --type threads.

Whatever my solution, it'll end up here. I'm putting my word on it.

 

[LINUS]

Also, @thatcabledude --- thx for the pic, I bet & give cred to you, betting your fix is what I'll find.

Between work & firewood, just haven't had a chance to trace, bit wanted to give cred where due - I'll be surprised if it's anything besides your suggest.

Will post better info later today, or tomorrow my 'day free'

 

[SUMMIT CRUISERS]

I found the thump on my 97. It's under the glove box and towards the center. As @thatcabledude mentioned, there is a servo motor that opens a door via a linkage. Once it gets to an end point, it hits a little plastic stop. It wants to go a little further than the stop, so I just nipped off the plastic stop. Here's a pic of the stop that I cut off. A screwdriver is pointing at it just below the nub. No more thumping. Btw to access the motor looks like a rear PITA.

 

[thatcabledude]

Nice!

 

[LINUS]

Thanks Summit!

I been busy working days / cutting wood eves - so I unintentionally took a ~10 day break from Mud, thanks for this as you kicked research to the curb & I can just get into it & fix it!

 

[SUMMIT CRUISERS]

Update...The thumping came back not too long after the fix I posted above on the fresh air lever. Yesterday I discovered a new problem. After removing the stereo to access the electric servo motor I noticed the above problem in the pic. The yellowish plug in the middle worked its way into blocking the operation of the motor at or below 75 degrees. To the left of the plug is an upward facing tab that tries to move to the right (into the yellowish plug) when at or below 75 degrees.

The fix. I ended up moving the plug to just above the other plug and secured it with a zip tie. As I look at it now, I'm wondering if the metal arm with the groove in it is bent and the plastic upward facing tab could become "untracked" over time as it moves to the right. I know it works now but it appears bent upward on the right side in the pic. Observing again, I notice that it appears also bent somewhat downward on the left side, so all should be fine.

All functioning properly now. What I did learn:
The servo motor operates at least 3 functions at once. Every rod/function need to work freely in order for the motor to function properly.
1. Make sure your heater valve on your firewall operates easily.
2. Make sure the lever and cable that opens and closes it (above and left of the glove box) operate easily.
3. Make sure the lever I posted a few posts above that opens and closes the fresh air door operates freely as well.
4. Lastly, situate the extra stereo plugs down low and to the left so the chance of them interfering with the electric motor is reduced.

Hope that helps another's thumping problem. @LINUS