Ultrasonic cleaning to restore the YH-409 HVAC sensor and park brake vacuum switch

[Hillbillycat]

Had read somewhere on this forum that these YH-409 HVAC sensors are fragile to take apart, with usually breaking. Someone mentioned ultrasonic celaning for there´s not much going on inside.

Since I have access to a Bandelin ultrasonic cleaner I grabbed the bull by the horns and threw the sensor in.
Removed the brass tube and vacuum harness. Before, during and after cleaning I wiggled the spring loaded diaphragm through the intake port with my pinky and tweezers and used light compressed air to blow things free/clean.

Bench testing the sensor after the ultrasonic cleaning looks promising: When applying hot or cold with a heatgun/hair dryer the vacuum on the larger line modulates, depending on position of the lever
In car test has to follow.
My AC is not working so I´m not sure how accurate the "in car test" will be. Up to now I only had full cold and no heat. Pulling the clear vacuum hose off of the gold servo motor like in the stickys described, flipped the heat duct door and I got full heat. My goal is to get working heat and cold control with this cleaned sensor, without the need to change to a manual cable setup.
AC service/rebuild is planned for future.

Btw:
Also restored the automatic park brake release vacuum switch that sits on the steering column with ultrasonic cleaning. Before the bath there was a vacuum leak and the slide lever inside was moving freely/easy. Lots of black/brown residue where the rubber seal rides inside was visible. After the cleanning the switch is 100% leak free. Had to apply a slight coat of silicone to the plastic for the rubber seal was sealing so tight you couldn´t even move the slider when vacuum was applied.

[Mainemantom]

Was the size of ultrasonic cleaning machine like for large jewelry ? Did you use cleaning formula ? How long was the cleaning cycle ?
That was good thinking to try it. Couldn't lose much if it failed.

[Mainemantom]

Was the size of ultrasonic cleaning machine like for large jewelry ? Did you use cleaning formula ? How long was the cleaning cycle ?
That was good thinking to try it. Couldn't lose much if it failed.

[gadget73]

Thanks for posting results. I had a feeling it might work, but not having a US cleaner or a bad sensor I had no way to prove that idea. Good news since those stupid things cannot be had anymore. Ultrasonic cleaners can be had for reasonable money so its potentially a good solution to the issue.

[Hillbillycat]

Hi,

I work as a dentist so I had acess to a Bandelin Sonorex RK102 Ultrasonic cleaner in our dental shop. I think it is what they use for large jewelry, too.
As formula I just used the burr/drill disinfection that was already in there. Any detergent or soap or dishwasher or washing soda should work, too.
The RK 102 cleaner has a heated bath that I had set to 50°C.
I let it in there for at least 20 minutes, sometimes rocking the mesh tray to move the parts.

[Hillbillycat]

Well, here´s the in car result:

the ATC still doesn´t work. Seems like the ultrasonic bath of the sensor didn´t work out. Too bad. It did work so well on the parking brake automatic release switch.
I plan to install a scooter/lawnmower fuel line shutoff valve on a bracket that I attach the temp lever bowden cable and vacuum lines from the sensor to the golden vac motor. This will hopefully enable me to control how much vacuum the golden servo motor gets manually. I hate the only cold or hot mode with the servo plugged/unplugged.

[sly]

The bimetal spring inside the cabin sensor is the thing that usually breaks and causes stupidity there. Not sure how you would go about fixing that though.

[87GrandMarq]

I’ve never had atc but I’d be interested to know how close that spring is to one on a choke cap for a carb. Just a thought.


Sent from my iPhone using Tapatalk

[sly]

Choke is a rather large ribbon while the one in the temp sensor is a rather thin wire.

[87GrandMarq]

Well then disregard my thought lol. But I wonder if someone could make a replacement wire like that. I don’t see why not.


Sent from my iPhone using Tapatalk

[sly]

The problem would be getting to it and installing it. I think it's spot welded to the base and the valve. It tends to break at the first bend between the valve and the center of the coil.

[gadget73]

I suppose it depends on the fail mode. The original one in my car would flip hot to cold randomly so I don't think it was a busted spring, but a wad of gak in the thing that caused it to not seal correctly.

[Mainemantom]

Hillbillycat, is this what you are looking for ? I have dealt with this seller. No problem.

eBay item number:
294171994002

[Lutrova]

If all of the parts that do the sensing and manipulating can be repaired and the only issue is putting everything back together, then maybe this is a problem some 3d printing can fix. We could design a new housing for the bi-metal and the vacuum valve, something that is more amenable to reassembly. I don't fully understand how the bi-metal and the temperature selection biasing manipulate the vacuum valve, but if the valve is bad there must be off the shelf options for replacing it. The only thing that sounds unobtainable is this bi-metal that's designed to move within standard climate control temps.

Does anyone have pictures of what the insides of one of these things look like?

[gadget73]

I'd actually not mind coming up with an electronic solution to the problem. Even if that involves replacing the vac servo with a small electric thing that has a feedback sensor. Just wouldn't be using the more modern servo that breaks and requires removal of the dashboard to access.