Unknown "clicking" from center dash area turning key off

[Nildecaf]

So, I'm getting 10 - 20 clear 'clicks' from what sounds like the center of my dash when I turn the key from on to off. Here's my troubleshooting so far:
Happens when I turn the key from on to off. Or if I've started the engine it happens when I turn the engine off. Doesn't happen with running the rig. Everything seems to be working normally on the couple of 3 hr. drives since the noise started.
I opened the generator bay and it still sounds like it's coming from the top center. But I can't see any obvious components that could be causing the noise.
The dash AC, heater and fan all work with no unusual noises. It occurs even if the dash fan is turned off before I turn the key off
The wipers and windshield washer work fine with no associated noise
It doesn't happen if I turn the key left (to enable the hydraulic jacks).

It's on a Freightliner chassis and I'm headed to Freightliner Gaffney on Tuesday for my annual service - so I'll obviously bring it up then. But I'd like to get your all thoughts before I take it in if possible.
Any suggestions appreciated.
Thanks in advance

[edgewant]

Does your rig have an Evans Tempcon cab heater/ac unit? If so it maybe a vacuum operated blend door that has a small vacuum leak.

Just a thought.

[Shadow5501]

On a Tiffin that noise is caused by a stuck or blocked door in the dash HVAC unit. Newer Tiffins use a system purchased from Denso. It has two blend doors - one for air output (dash, floor, etc) and one for fresh/recirc. Each door is controlled by a servo motor. At startup and shutdown the servo motor sweeps the door through its full range of operation. If the sweep is unsuccessful, you get the clicking as the servo retries.

Try pressing the fresh/recirc button (center of right hand knob) while the unit is powered up. See if that riggers the clicking. If so, it’s the fresh/recirc door that is blocked.

You can download some manuals and schematics here: https://www.densoheavyduty.com/hvac-systems to help locate the two servo motors.

Mine had this fault from new, the dealer corrected it as part of the punchlist checkout. I think they accessed it from a removable cover in the dashboard, however I have a different model Tiffin than do you.

[Deznut]

my Nissan truck (2006 Frontier) does it as many other Nissans..here's a Youtube "fix" - not very "professional" but it works and eliminates the constant ticking ( some use small clothes pins, I used some small clamps from HF)- the trick is NOT to let the door close all the way...hth

https://www.youtube.com/watch?v=WbzOkVOhMJ4&t=164s

[bneumann]

Thanks so much for explaining this item .... was wondering & thought it was a fan touching something .... always hear it when turning key & always went away after a few seconds. In the back of my mind to actually look for source.
Recirc door trying to overclose makes sense.

Does anyone know where Denso unit is & how to access ? ... must be easy access (or with motorhome probably not) since one needs to change filter.

Doubt if filter was ever changed, probably a good idea. The video showing simply to add a tie wrap seems pretty easy, if the unit is accessible.

Before having to twist / contort to search under dash .... would it be under the upper removeable panel on top dash or near generator front access?
Anyone know how to access ?

[Nildecaf]

Originally Posted by Shadow5501

On a Tiffin that noise is caused by a stuck or blocked door in the dash HVAC unit. Newer Tiffins use a system purchased from Denso. It has two blend doors - one for air output (dash, floor, etc) and one for fresh/recirc. Each door is controlled by a servo motor. At startup and shutdown the servo motor sweeps the door through its full range of operation. If the sweep is unsuccessful, you get the clicking as the servo retries.

Try pressing the fresh/recirc button (center of right hand knob) while the unit is powered up. See if that riggers the clicking. If so, it’s the fresh/recirc door that is blocked.

You can download some manuals and schematics here: https://www.densoheavyduty.com/hvac-systems to help locate the two servo motors.

Mine had this fault from new, the dealer corrected it as part of the punchlist checkout. I think they accessed it from a removable cover in the dashboard, however I have a different model Tiffin than do you.

Shadow5501 - Thanks for the info, especially the info on the deferential diagnosis. I was able to confirm that my issue is with the recirc/outdoor air blend door servo.
I brought up the problem while at Gaffney Freightliner for my annual service only to find out that it's a 'house' (Tiffin) component not something Freightliner can service.
Also I haven't been able to figure out how to access the servo from the manuals you provided, but it seems likely that it might be via the dash. I don't have the hutzpah to begin disassembling my dash for a non critical issue at this time so I'll have to wait until I either find specifics on how to access the servo or until we get to a shop that can fix it.

[Nildecaf]

Deznut - Thanks for the video. It helped show what is going on with the servo. It may come in handy if I ever figure out how to access the blasted component. [emoji1787]

[Deznut]

Ndecaf - you are welcome...my Frontier has been "fixed" that way ( HF miniature spring clamp, clamped to the "grid") ) since 2016...I'm getting too old to climb in upside down head first into the passenger seat and connect a ty-wrap ( my wrist doesn't''t bend that way anymore) ...here in Nevada is does get cold and the Heat/Defrost doesn't seem to work any worse....but living in southern Nevada it's the A/C that's gotta work ...and even with the little clamp the A/C works great....hth

[Dutch Star Don]

Originally Posted by Shadow5501

On a Tiffin that noise is caused by a stuck or blocked door in the dash HVAC unit. Newer Tiffins use a system purchased from Denso. It has two blend doors - one for air output (dash, floor, etc) and one for fresh/recirc. Each door is controlled by a servo motor. At startup and shutdown the servo motor sweeps the door through its full range of operation. If the sweep is unsuccessful, you get the clicking as the servo retries.

Try pressing the fresh/recirc button (center of right hand knob) while the unit is powered up. See if that riggers the clicking. If so, it’s the fresh/recirc door that is blocked.

You can download some manuals and schematics here: https://www.densoheavyduty.com/hvac-systems to help locate the two servo motors.

Mine had this fault from new, the dealer corrected it as part of the punchlist checkout. I think they accessed it from a removable cover in the dashboard, however I have a different model Tiffin than do you.

Great diagnosis and simple test procedure!

[Nildecaf]

Originally Posted by Shadow5501

On a Tiffin that noise is caused by a stuck or blocked door in the dash HVAC unit. Newer Tiffins use a system purchased from Denso. It has two blend doors - one for air output (dash, floor, etc) and one for fresh/recirc. Each door is controlled by a servo motor. At startup and shutdown the servo motor sweeps the door through its full range of operation. If the sweep is unsuccessful, you get the clicking as the servo retries.

Try pressing the fresh/recirc button (center of right hand knob) while the unit is powered up. See if that riggers the clicking. If so, it’s the fresh/recirc door that is blocked.

You can download some manuals and schematics here: https://www.densoheavyduty.com/hvac-systems to help locate the two servo motors.

Mine had this fault from new, the dealer corrected it as part of the punchlist checkout. I think they accessed it from a removable cover in the dashboard, however I have a different model Tiffin than do you.

Shadow 5501 - Thanks again for the info. While I was in Red Bay for another issue I had Tiffin fix the fresh/recirc blend door servo problem. It took them all of 20 min and cost me $45. Tech said the servo arm had to be put back on. I'm pretty sure it did require pulling part of the dash out to access though.