1960s 1967 Heater troubleshooting - no vac to servo

[kyle242gt]

Hi all - chipping away at getting my heater working in my 1967 Deville.

I've got about 2psi vac to servo at 85, might be a little lower when set to 65 (might be hallucinating).

I do have manifold vac to transducer (22" or so).  Have not checked voltage to transducer yet.

Reading prior threads here, I gather that the rotary valve in the servo is a common culprit.  I have a buddy who used to work on these "back in the day" and he says the rotary switch on the control head is a common problem.

There's ~15" vac to lower (yellow) vac line on the heater valve.
https://www.eldorado-seville.com/resources/Untitled-Folder/BG-AC-vacuumdiagram.jpg
About 12" at the upper (red) fitting on the valve.  Not sure what the story is there, vac leak in the heater valve?
About 10" at the master switch.  That's indicative of a vac leak somewhere.
But the air doors certainly seem to be working (dash with no vac to servo, windshield on ice, floor with vac applied to servo).

FSM says 14" needed at master switch.  Would that lack of high vac (which runs to both servo and control head) cause the temp dial and amplifier to not function properly?  Not sure I understand how the electrical system (temp sensors, rotary dial, transducer, amplifier) interacts with the vacuum system.

My question at this point: keep working on the vacuum, or should I start looking at the electrical items?

[V63]

I would verify the vacuum heater valve is actually opening the valve, maybe by pass the valve entirely and plumb around it so guarantee heater core is getting hot water.

["Cadillac Kid" Greg Surfas 15364]

Check the voltage to the transducer both at a 65 degree dial setting and at 85 degrees
Greg Surfas

[kyle242gt]

Thanks fellas -
I do have hot water - connecting servo straight to manifold vacuum gets hot air in cabin - and boy howdy does it work well.  Air's not super hot, but man does it heat the car up in a hot minute.

Will check voltage at transducer (10V = 65, 0V = 85 if I recall right) and report back.

[cadillactim]

Check your transducer. Unplug black wire and output to servo should be at least 10 inches. Apply battery voltage to black wire vacuum should drop to less than 3 inches.

Tim

[kyle242gt]

Thank you - getting 0V to transducer at 85 and 4V at 65.  FYI ambient temp is 50 and cabin temp about 60 - I think this would explain why 65F voltage is pretty low.

Sounds like the tranducer's bad or stuck.  I get roughly 3" at all times.

Are these the sort of things that are user serviceable? Or respond well to a good old knock with a hammer (in jest, as the manual states to be careful not to impact it on anything)?  Caddydaddy sells refurbished ones, so it stands to reason it's repairable, just a question of if a semi-intelligent fella can do anything with it.

["Cadillac Kid" Greg Surfas 15364]

Kyle,
Before you condemn the transducer the low voltage indicates that there is still a call for heat. try and warm up the in-car sensor with something like a hair dryer on low so that the temperature (of the sensor) stabilizes at something like 85 degrees. then roll the temperature dial to 65 and see what the voltage is to the transducer.
Greg Surfas

[kyle242gt]

Thanks Greg - will give that a shot.  If I get the in-car sensor to 85, set temp dial to 65, I should get something like 10-12V, right?  Or, even more simply: set temp dial to 65, connect voltmeter to transducer, then begin warming the in-car sensor, I'd see voltage rise steadily...?

But check my reasoning if you will - I get 0V at 85, but no vacuum through transducer.  Shouldn't the transducer default to open?  If if no voltage to transducer (due to something as simple as a disconnected wire), shouldn't it go to full vac, and full heat?  (diagram states low voltage = high vacuum / high voltage = low vaccum)

//edit - as luck has it, the sun came out, so the car got quite a bit warmer inside.  With the transducer wire disconnected, I get 12-14V 65-85F.  Might just be the battery topping up post-start. Sort of surprised to see that voltage increased at higher temp... Guessing that the no-load voltage (transducer disconnected) from the control head is not symptomatic of anything, since the voltage responds as expected to the temp dial.

When connected to transducer, it goes from 0 (85) to 10 (65).  As the car cooled off (doors open), the 65 voltage decreased a bit.

Still really seems like transducer is just stuck in full AC mode.

[cadillactim]

Do the test I mentioned earlier. That isolates the transducer so you can test it specifically.

Transducer defaults to maximum vacuum (at least 10 inches) with no voltage.

Tim

[kyle242gt]

Do the test I mentioned earlier. That isolates the transducer so you can test it specifically.
Transducer defaults to maximum vacuum (at least 10 inches) with no voltage.

Thanks Tim - sorry for missing this stage.   Really appreciate your confirmation that it should default to max vac!  I did reason it out:

But check my reasoning if you will - I get 0V at 85, but no vacuum through transducer.  Shouldn't the transducer default to open?  If if no voltage to transducer (due to something as simple as a disconnected wire), shouldn't it go to full vac, and full heat? 

But realize that there could be some electrical gremlin involved making the transducer react to voltage that didn't appear on my voltmeter.

Just disconnected the wire to be sure:  Transducer wire disconnected, still that same barely 3" of vac to the servo.

[kyle242gt]

Just one more followup:
Transducer unplugged
20" vac to small (top) hose
3" vac from large (lower) fitting
Hose from transducer to servo, when connected engine-side to vacuum source, has 20" of vacuum dash-side (IE transducer-to-servo hose is not leaking).

At this point, barring better ideas, I think I'll take the top of the transducer apart, see if I can make sense of how it works, and clean/unstick/whatever I can think to do.

[E Masters]

The transducer has a small flat head screw at the bottom for adjusting the tension on the internal wire. It may just need a quarter turn in or out. Turning it out gives more vacuum and heat. Turning it in gives less vacuum and cold.

There is also a voltage adjuster between the temperature dial and side on the dash. I use a credit card to hold the internal star wheel. It's for fine tuning.

[kyle242gt]

That is excellent info, much appreciated.  Was aware of the adjustment at the control head, but not the transducer.  Will give that a whirl!

[kyle242gt]

Screwing it out got to 5" max vac, no change from that when adjusting temp dial.

So I took it apart:

Wire gets power from control head, must heat and expand. 

That lets the metal hook doodad rise,

which moves diaphragms up.  There are two diaphragms, servo side (lower) connects to hook on the outside circumferance. 

The engine side (upper) has a pin that protrudes through the lower.  (perspective is pretty weird, but it's the round item in the center; the torn piece is the section that goes around the outside of the hook.)

Appears this pin should be connected to hook, but I didn't see any indicator of this for sure (clip, epoxy, whatever).  If the upper diaphragm isn't pulled down, there's no flow from the upper port.  Pulling it down manually, I get vac through to lower port.

Didn't bother jigging things up to measure if the wire really does expand under power... but I think I have the theory of operation figured out.

Tempted to epoxy hook, diaphragm, and pin together, but I don't know what the baseline relationship between the two diaphragms is supposed to be. 

What do you think?

[kyle242gt]

NOS transducer en route..!

[Cadillac1967inthenorth]

Screwing it out got to 5" max vac, no change from that when adjusting temp dial.


Tempted to epoxy hook, diaphragm, and pin together, but I don't know what the baseline relationship between the two diaphragms is supposed to be. 

What do you think?

Must be quite hard to restore a transducer to perfect working order. I have two ATC from the sixties, one cadillac from 1967 and a 1969 Autotemp from chrysler. Both transducers was working when I bought them. I had vacuum leaks and mixed hoses. The service manuals are great and very helpful! Its not that hard to understand the systems, but you have to read carefully before you start the repair.

Here is the power servo in my 1969 Imperial. I took the black box apart to check the hoses and I also opened the valve. In the video the servo moves from side to side when I turn the temp dial between 65 and 85 (was around 70-75 outside). I haven't got a video of my 67 Cadillac but it works the same way with one difference. In the Cadillac system the servo also regulates the blend door. In the Imperial, its vacuum that modulates the heater valve. 

 

[E Masters]

I rebuilt mine using the inner bladder rubber from a soccer ball.

[kyle242gt]

Received transducer today, connected to vac, and servo went to max hot.  That's a good sign!
Installed and connected to power, and son of a gun, 65 gets servo to about half mast (it's about 50F right now), 85 goes to max hot. 

Fingers crossed that this holds up.  Pretty neat to see this old tech work so well after all the years and neglect. 

Thanks much to everyone for the help troubleshooting.  Planning now to drive and enjoy the car until spring, then dig into the AC.