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

  1. #21
    Carthago delenda est Lutrova's Avatar
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    Keeping the outward appearance of stock-ness seems desirable, so some sort of 3d printed housing would be necessary to keep the cable end fixed to the pot. The black tube that runs up to the firewall - is that there just to help draw air from the cabin past the temp sensor?

  2. #22
    I'm an air-conditioned gypsy gadget73's Avatar
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    No modern climate control head, has to be the stock slider rig. Was thinking a pot with a crank arm so the cable attaches like it did to the vacuum regulator.


    The tube is to pull air past the sensor so it reads in-cabin temperature. The other end goes to the blower housing so it creates a draft. Prob have to duplicate that with an electronic sensor to get a reasonable cabin read. The EATC systems did it that way too.

    86 Lincoln Town Car (Galactica).
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    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

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  3. #23
    Beater gonna beat sly's Avatar
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    Yeah... I forgot about the temp input, but that's all very doable... The hardest part is the vacuum solenoid for converting the pwm signal to variable vacuum bleed. I don't know if there is a unicorn that would fit in the form factor. If I still had a box, I might work on the project. Would be something fun to do at work in my spare time, but I have nothing to test it on.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
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    ... and it should all work like magic and unicorns and stuff.
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  4. #24

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    Yes, this is the part. Good to know. Thereīs ī89 a parts car 2 hours away from me in Germany. Iīll try my luck there first.

    Say, is a working AC mandatory for the ATC sensor to work properly?

    Fact is the sensor works on the bench, if I apply heat or cold compressed air.
    I even removed the sensor once again and changed the setting with the star wheel adjuster on the back of the lever. But to no avail. Still full cold.
    Last edited by Hillbillycat; 05-25-2021 at 04:05 AM.

  5. #25
    Wagon Addicted Tiggie's Avatar
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    ATC doesn't need A/C to work. It will still try to regulate the temp but can't cool beyond the outside air temp. My 88 had the full cold issue when I got it. Replaced the sensor with a lucky newer junkyard find it was happy.
    1990 Country Squire - weekend cruiser, next project
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  6. #26

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    Thank you. So Iīll either buy the ebay one or hope that the one in the parts car is still working.

  7. #27
    I'm an air-conditioned gypsy gadget73's Avatar
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    working AC is mandatory for proper driving enjoyment though.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  8. #28
    Wagon Addicted Tiggie's Avatar
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    Wonder if there is any chance of this older design working, or using parts from it?

    https://www.ebay.com/itm/27476836783...5ggJgQ&LH_BO=1
    1990 Country Squire - weekend cruiser, next project
    1988 Crown Vic LTD Wagon - waiting in the wings

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  9. #29

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    Got me the sensor from the donor car - still not working.

    Carefully took my old (ultrasonic cleaned one) totally apart. No broken bimetall, no rips in the diaphragm, nothing that would indicate a malfunction.
    Why the hell isnīt it working then?

  10. #30
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    The corrugated hose needs to be on the mount at the firewall to get airflow through the sensor. If that hose isn't hooked up to the port at the firewall, it won't work. If the port is broken and doesn't hold the hose, it won't work. If the vacuum lines won't seal good, it won't work. If there's a vacuum leak in the system, it won't work.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  11. #31

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    I suspect a vacuum leak somewhere. Vac lines to the servo motor and sensor are tight, same as corrugated hose and connector at firewall and free of any debris.

    On my 1984 F250 diesel truck (with itīs simple vacuum circuit compared to the Town Car) the HVAC vacuum doors can be adjusted after the engine is shut off (untill the vacuum source is empty of course). So the system stores vacuum.
    Not so on my Town Car.

    Thatīs why I suspect a vacuum leak. But since the circuit is way more complex it might be normal for not sotring vacuum after shutoff. But thatīs a thing I donīt know and wasnīt able to read from the shop manuals.

  12. #32
    GMN Regular DerekTheGreat's Avatar
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    It's most likely that thermal switch on the heater core hose. My original was bad, but then I replaced it with a "Motorcraft" unit and it was even worse. Upon acceleration the air would drop out from the vent position and to the defrost position, which is what it does with zero or next to no vacuum. I spent some time rebuilding one thermal switch from three, if I remember right. It's been great ever since. Never tested to see how long the system holds vacuum though.
    1985 LTD Crown Victoria - SOLD
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  13. #33
    Beater gonna beat sly's Avatar
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    The check valve could also be bad. There's one on the vacuum tree with the fat connection to the tree and 2 tails to the HVAC and soup can vacuum reservoir. That's the usual failure as those only last about 10-15 years. Motorcraft YG-337.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  14. #34

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    I also suspect the YG-337 check valve. Have a good one from the donor car so I will swap them out and see.
    Thermal Blower Lockout Switch is already deleted and bypassed by a piece of pipe, vacuum lines plugged, connector jumpered.

    Air stays on vent or any other position during acceleration. No switching to defrost. I only notice it switches from cool to heat and blows hot when speeding up a grade on the Autobahn?!?!

  15. #35
    I'm an air-conditioned gypsy gadget73's Avatar
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    thats vacuum loss symptoms. Seems like the temperature shifts before where the air comes out does but with no vacuum it defaults to hot defrost.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  16. #36
    Beater gonna beat sly's Avatar
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    If it's anything like the 88 MGM I had, it blew out of all of the vents on every setting, but blew the hardest out of whatever it was set to. Air plenum leaked like crazy and you would get a little out the defrost and floor even with panel set. Middle of summer and your feet are freezing because of the air leaks from the ducts.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  17. #37
    I'm an air-conditioned gypsy gadget73's Avatar
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    thats usually the air doors are broken off the hinge. One end of it moves, the other flops around so it never actually seals. Had that issue on my Towncar, used some teeny hinges to fix the doors. Once you get the plenum out its not that awful of a job to fix but getting the plenum in your hands, and then drilling out the pile of rivets to split the thing open is a real pain in the ass.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  18. #38
    Beater gonna beat sly's Avatar
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    It wasn't quite that bad yet... but nothing sealed so you could still feel a little puff everywhere else while one was blowing hard. It wasn't a major leak, but enough that on a hour drive somewhere, your feet would be frozen while the sunny bits up top were just right.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  19. #39
    all the CFI are belong to me
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    Late to the party, but some considerations about the vacuum ATC stuff:

    While I only have a sample size of 3 vehicles equipped with this part, I am an aggressive hoarder of spares harvested in junk yards. I do not sell them, that isn't the point here, it's more to establish sample size.

    Basic operating theory: vacuum is applied to the servo to change the temperature to be "less hot". In the absence of vacuum, it is hot. In the presence of vacuum, it is cold.
    If the temperature drifts from cold to hot, it is because not enough vacuum is being given to the servo. This is likely to be an external leak (e.g. vacuum sucking in outside air through a leak instead of acting on the system).
    If the temperature drifts from hot to cold, it is because too much vacuum is being given to the servo. The only way that this is possible to happen is because the ATC sensor/valve is not doing what it's supposed to do, properly.

    All of the ones I have observed that do not work properly, appear to work "mostly properly" but very gradually over a long time will leak enough vacuum through that you have to progressively shift the temperature slider hotter and hotter in the winter until eventually it's all the way to the hot side, and yet you're still getting cold air. I have not yet found a single one of this part with an outright broken spring. Others have reported broken springs, so I'll never say they don't break, but it seems that the more commonly observed failure mode is a loss of accurate vacuum regulation.

    We do not have concrete evidence to support what actually causes this failure. The obvious thing would be a failure to fully seal the vacuum valve within, and one of the common opinions as to why that might happen was dust or dirt contamination. The ultrasonic cleaning approach clearly is targeted at that, but without a full disassembly, we don't know that it successfully got into the true problem area adequately...it likely did but we don't actually know that.

    Accordingly with all that, I would not pay any sort of meaningful money for one of these, would probably not even consider buying New Old Stock (since we don't know that the failure isn't going to come with age), and I'd consider it (in the presence of this knowledge) unfair and unethical to, for example, make a claim with the eBay money back guarantee because one received did not actually work as promised. The seller might know the car behaved properly for 5 minutes. My car behaves properly for 5 minutes, it's after 40 or so that it really shows the symptom.

    These are able to be disassembled without breaking them. However, you will lose parts, which nets the same result in the end. There is a super tiny little ball-bearing-like thingy that goes in it and likes to immediately disappear.

    My vote for a proper long term solution to this is 90s EATC swap, including the unpopular actuator with the gears that melt, and figure out a way to mount it so it isn't a nightmare to change. I will note that it is probably so failure-prone (the EATC actuator) because of the thermal conditions where it is located.

    Now, all of THAT being said, I believe from the most recent developments in the thread that your (OP) issues are actually a vacuum leak. The check valve, lines, and reservoir canister are priority suspect items in my experience. The line in the engine bay that snakes around to the reservoir by the fender is my #1 suspect to check first. I've seen multiple splits where heat, time and friction have not been kind to it.
    Last edited by kishy; 06-09-2021 at 12:27 AM.

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  20. #40
    Carthago delenda est Lutrova's Avatar
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    In my own recent explorations of this problem, I traced my vacuum leak to the (non-functioning) ATC sensor. I had already capped and bypassed the TBL sensor, replaced the vacuum reservoir, and checked the check valve. The ATC sensor had failed in the traditional way, defaulting to full cold, or providing vacuum to the temp servo. But when tested with a vacuum pump and when driving on long uphill climbs it would lose enough vacuum to send the servo to hot. I confirmed this by bypassing the ATC sensor with a line going straight from vacuum supply to the clear servo line - no issues cruising uphill. From your suggestion to me about the bypass with a 'T' and screw for basic temperature control, it sounds like you've already got that part figured out.

    If something else in the system is leaking, a great place to check is right behind the radio. I believe all the HVAC vacuum lines apart from the vacuum reservoir line pass through a connector here. Disconnecting it and testing each line is real easy, and everything should be verifiable against the EVTM.

    Something I still don't understand is whether an ATC sensor in perfect working order leaks vacuum when set to hot, or if it caps off the vacuum supply line to keep the rest of the system from running out. If it does just leak in hot instead of pass vacuum to the servo, the check valve and reservoir should mean that there's enough reserve to keep everything else happy. But maybe these hill conditions are long enough that they drain the vacuum reservoir. I can't imagine Ford would've designed the system such that driving on mountain highways would kill your cool air.

    Can anyone confirm whether a working ATC sensor holds vacuum in a bench test?

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