I'm currently troubleshooting the vacuum system on my 67 DeVille convertible which only has heat and defrost. (No AC)
The way I understand it is that there is a vacuum line from vacuum source (such as manifold) and that routes to a vacuum switch (lefts for heat, defrost and "off") in the cab. The switch then has two lines that run to the heater diaphragm and the defrost diaphragm.
What I have tested so far...
- Pulling from source hose with "Defrost" set on switch = success
- Pulling from source hose with "Heat" set on switch = fail
- Pulling from source hose with "Off" set on switch = fail
- Pulling directly from "Defrost" diaphragm = success
- Pulling directly from "Heat" diaphragm = success
So here is where I'm stuck...
- Is it more likely for the switch to fail or just a hose?
- Should the "off" selector on the switch show vacuum when pulling from the source?
- Should I be able to remove the hoses from the switch distribution block? I tried and they don't seem to want to come out. See pic below
An oe shop manual is the best way to track this down, also those hoses are molded to the connector.
Thank you Dave. I was wondering about that.
Is there a place to buy a new connector/hoses or do I need to re-build it by removing the hoses and re-molding hoses back into the connector?
Very strange. The hoses should never come out of the connector! :o
There is a rotary valve that routes the vacuum to the different hoses. Unless your connector is in good shape you will have all kinds of vacuum leaks!
However, even if you fix the connector you could still have some vacuum leaks through a warped rotary valve.
Check my restoration blog for some details about the A/C Vacuum system.
Thanks DeVill68. I have tested the diaphragms and they work as they should. But it appears I have leaks between the connector and the diaphragms. The switch may have issues as well, but my thought is that I should have good vacuum from the connectors to the diaphragms first.
Assuming that, what do I do?
- Cut the vacuum line a few inches after the connector and then extend with new hose?
- Remove the lines from the connector and try to re-attach new lines?
- Find some source for NOS connectors w/ hoses?
Thoughts?
Thanks
C
Hi
So, I used my second spare vacuum tank (but you can unbolt your original vacuum tank or connect long enough hoses) to hold the vacuum. On the outlet (the outer port) I connected a vacuum source - I happened to have a vacuum pump. You could also use a hand pump, but it would probably take a little while to suck it out.
On the inlet (where you connect the vacuum units) I connected a tee and a vacuum gauge.
I connected a hose from the tee to the unit I wanted to check, for example a flap of the A/C System. Make sure you check the flap and its hose. Then I switched on the vacuum pump and pumped the vacuum up to about 20'' then I switched the pump off. The vacuum stays inside the tank because of the valve. Then I could watch via the vacuum gauge how long it took for the vacuum to drop. If it drops in like 5 to 10 seconds you have a problem. If it only drops after a few minutes it is ok.
You want to use a vacuum tank or something large to apply a strong enough vacuum, I found that it is difficult to judge just using a hand vacuum pump without vacuum tank.
(my remote trunk release actually works still fine the next day when parked over night!! 8) )
First picture shows the vacuum tank and pump.
Second picture shows how I checked the vacuum booster on the firewall, where the A/C head unit in the dash is connected to.
With this apparatus I checked every actuator and every hose and every tee, etc. None of my actuators where bad and none of the hoses. I did find however that I had to snip off a little bit on the end of the hose (maybe half an inch) to fully seal the connection.
Vacuum leaks where at the neutral safety switch (miscalibrated), on the rotary valve of the head unit (dash) and on the rotary valve of the power unit on top of the firewall.
Good luck!
Best regards,
Nicolas