Rotary HVAC control to fix bad ATC

[pollock]

My ATC has gone bad. I studied up on this thread.

http://www.grandmarq.net/vb/forum/technical/box-tech/electrical-and-wiring-hvac-vacuum-cfi/41175-project-rotary-hvac-control

Can I use that swap to effectively bypass the ATC and just have non-automatic control?

[friskyfrankie]

What exactly has gone wrong? O-rings? something else?

[pollock]

The ATC sensor. Classic no-heat symptoms as described the main HVAC sticky thread. I currently have it rigged with a small valve so I can adjust temperature. Would like a more elegant fix.

[kishy]

Some considerations, having not read all of the swap project that you linked (but being aware it had been done):

In pre-90 boxes, ATC vs non-ATC cars have different linkage geometry for the temperature blend door because the metal rod that gets pushed on by either the cable (non-ATC) or vacuum servo (ATC) is shaped differently. e.g. push and pull are reversed between them, and the options for mounting hardware to operate that linkage vary between them.

I don't think this will be easy. The car that got swapped in that thread did not have ATC. You'd basically be looking at doing the following:

1. Convert to manual climate control
2. Swap the controls to the rotary style

But you could realistically also just do 1 on its own and solve your problem.

If you wanted to retrofit the 90+ ATC system, which is electronic and therefore referred to as EATC, that would be an option to get modernized controls, more reliable blend door operation, and still having the ATC functionality. But that's a little more involved. It's been talked about before but I don't recall if anyone actually did it.

[friskyfrankie]

Is the sensor available? What year/model vehicle? Depends how old the car is - OEM (or even aftermarket parts) may be difficult to find. Is the rest of the system intact except for the sensor?

[Arquemann]

Is the sensor available? What year/model vehicle? Depends how old the car is - OEM (or even aftermarket parts) may be difficult to find. Is the rest of the system intact except for the sensor?

Motorcraft YH-409, pretty much unobtanium. Mentioned now and then on the forum.

[friskyfrankie]

Here is a possible link. Check with them to see if it is really available!

https://www.2040-parts.com/84-85-86-87-88-89-motorcraft-yh-409-ac-temp-sensor-lincoln-town-car-mercury-ford-i344082/

[Lutrova]

If you want to go down the ATC sensor route, take a look at this thread, particularly after about post 39 or so:

http://www.grandmarq.net/vb/forum/technical/box-tech/electrical-and-wiring-hvac-vacuum-cfi/51810-ultrasonic-cleaning-to-restore-the-yh-409-hvac-sensor-and-park-brake-vacuum-switch

Hillbillycat and I opened up our sensors and seemed to have had some luck restoring function to them. I can't say how his is doing, but my car went from total sensor failure to at least some temperature control after I inserted a piece of wood to keep the needle valve in position. You might give that a try before anything else, as it would be the cheapest and least labor-intensive fix.

[friskyfrankie]

If you want to go down the ATC sensor route, take a look at this thread, particularly after about post 39 or so:

http://www.grandmarq.net/vb/forum/technical/box-tech/electrical-and-wiring-hvac-vacuum-cfi/51810-ultrasonic-cleaning-to-restore-the-yh-409-hvac-sensor-and-park-brake-vacuum-switch

Hillbillycat and I opened up our sensors and seemed to have had some luck restoring function to them. I can't say how his is doing, but my car went from total sensor failure to at least some temperature control after I inserted a piece of wood to keep the needle valve in position. You might give that a try before anything else, as it would be the cheapest and least labor-intensive fix.

Sounds reasonable but only if a new sensor can not be found. If it can be found and expense is not an issue, that would be the best solution especially since the part is already out. Not the cheapest solution but still the best unless you can ensure complete function after a repair.

[Lutrova]

I suppose it boils down to how much trust you put in NOS sensors. There's some speculation that the failure of these things could be due in part to age, which will affect parts on a shelf as much as ones in a car. I would make sure whoever I bought from had a good return policy.

[kishy]

only if a new sensor can not be found

Reading between the lines, I'd guess that you're a relative newcomer to the issue of pre-1990 ATC.

The sensor is a fairly sophisticated vacuum valve acted upon by a bimetal spring. The spring expands and contracts based on the temperature of the airflow through the sensor, and accordingly acts on the vacuum valve to pass metered amounts of vacuum to the servo, providing for "more hot" or "less hot" until the desired amount of "springiness" is found. The spring has a tension input from the temperature slider on the controls, so when you slide it, you put a certain amount of preload on the spring.

These parts are unobtainium. They simply do not exist new out there, anywhere. Occasionally one turns up on eBay for 300 bucks, but I don't even think I'd be willing to pay that for them - as Lutrova noted, there is some belief that age is one of the factors that make them stop behaving properly in addition to just dirt contamination.

It is a junkyard "must pull" item, when one turns up with a manufacturing date stamped on it that is significantly newer than the car it's installed in (and bonus points when the vacuum line is still connected to the servo, because it means it probably works at least a little). I've seen them as new as 2003ish.

We will reach a point with these cars, and honestly we may be sitting on top of that point right now, where we're going to need a go-to retrofit solution that becomes as ubiquitous as the 3G upgrade. I have a feeling the option that lets us keep ATC is probably an EATC retrofit and 3D-printing parts to mount the blend door actuator.

[Arquemann]

+1 what kishy said.

My cars ATC has worked fine most of the time, but it seems the temp control has some fits sometimes. I don't want to meet the day when the temp sensor kicks the bucket, but I definitely don't want to be without a plan if/when it fails.
Though I kinda want a manual temperature control, just refitting the temp ATC temp slider to directly move the blend doors, vacuum-operated or manually.

[sly]

Not sure what vehicle year is being dealt with here... so since it's in box tech...

The trouble with just swapping the cable (or moving the ATC one down to actuate the door directly) is that the ATC models move the door exactly opposite of the manual models. So a direct cable mount on ATC car would be cold in hot position. To fix this, you have to fabricate something on the actuator arm to either mount the cable from the back or reverse the rod direction (turning it into a Y and using the other side of the uprights for actuation) and of course the bracket needed for that repositioning.

[friskyfrankie]

I did find at least one source and gave the link. Of course, verification will be required!

[friskyfrankie]

Reading between the lines, I'd guess that you're a relative newcomer to the issue of pre-1990 ATC.

The sensor is a fairly sophisticated vacuum valve acted upon by a bimetal spring. The spring expands and contracts based on the temperature of the airflow through the sensor, and accordingly acts on the vacuum valve to pass metered amounts of vacuum to the servo, providing for "more hot" or "less hot" until the desired amount of "springiness" is found. The spring has a tension input from the temperature slider on the controls, so when you slide it, you put a certain amount of preload on the spring.

These parts are unobtainium. They simply do not exist new out there, anywhere. Occasionally one turns up on eBay for 300 bucks, but I don't even think I'd be willing to pay that for them - as Lutrova noted, there is some belief that age is one of the factors that make them stop behaving properly in addition to just dirt contamination.

It is a junkyard "must pull" item, when one turns up with a manufacturing date stamped on it that is significantly newer than the car it's installed in (and bonus points when the vacuum line is still connected to the servo, because it means it probably works at least a little). I've seen them as new as 2003ish.

We will reach a point with these cars, and honestly we may be sitting on top of that point right now, where we're going to need a go-to retrofit solution that becomes as ubiquitous as the 3G upgrade. I have a feeling the option that lets us keep ATC is probably an EATC retrofit and 3D-printing parts to mount the blend door actuator.

Not new at all to this issue but I always like to look in every nook and cranny before giving up. As you said, it is a fairly sophisticated piece so playing around, inside of it is not recommended unless you have no other choice. As always, there is never a guarantee any NOS part will still work.