Scuttle Vent Closing with Heater Switch On

[YoungJagFan]

I've got yet another question (my new 1965 car needs a lot of TLC), is the scuttle vent supposed to open when the heater button is pushed?
The other day I decided to switch on the heater but when I pressed the vacuum switch for heat the vent wouldn't open. Now, the vent opens when I press the fresh air button with no issues and of course closes with the off button. I also ran a cycle from left to right...pressed the air switch, vent opens. Pressed the heater switch next, vent closes. Pressed the heater switch again, still won't open. On a final note, does it matter if the temperature slider is over to heat first? I haven't used the heater except for one time when I bought the car five months ago, I can't recall if I used the slider the other day before pressing the vent switch.
Should I start looking for a vacuum leak somewhere or is it just my unfamiliarity with the system?

[cass3958]

Glyn will post a picture I am sure to help but the three switches are fairly straight forward.

Air opens the scuttle vent and allows fresh air in to the cab.

Heat opens a vacuum switch which is under the heater in the engine bay and allows hot water to flow in to the heater matrix. Neither of these are connected as there are separate tubes going to each.

Off turns off the vacuum to both so both will be closed. If the scuttle flap is opening and stays open you do not have a vacuum problem.

Someone will correct me if I am wrong but I think you can have the heater switch on and have the air switch on to open the scuttle flap as well. I will have to go out to my car to check.

The heater slider does not have any effect on the three buttons as this just opens and closes a flap in the heater matrix via a wire to adjust the amount of hot air that is directed into the cabin. It does not actually adjust the temperature in the heater matrix it just allows cold air to mix with the hot thereby cooling it down.

[YoungJagFan]

Ah! It is starting to make sense now! I guess where the issue lies is why the vent flap closes when Heat is pressed. When Air is pressed in, the flap pops up like new. As soon as I press Heat, the flap drops again as if I pressed Off. Maybe it is the switch cluster?

[cass3958]

If you look at the back of the three button switch the Air and Heat buttons have a bypass connecting them if I recall correctly so when you push Heat it basically closes off the Air button.

I have just checked mine and if I push Air the flap opens.

If I push Heat the flap closes.

If either Air or Heat are pushed and I push off they both close and the heat goes off and the flap closes.

But I also found that if you push Air the flap opens and if you push Heat it closes but if you then push Air again the Heat button stays in and the flap opens. I think this is to drive more fresh air in to the heater which then produces more hot air in the cabin.

[YoungJagFan]

Thank you Rob, you saved the day! I've been sitting here at work all morning trying to figure out why it was working that way. That makes perfect sense, especially after looking at a diagram of the vacuum circuit coming off of the heater controls. Other than my confusion, the vacuum works great on opening the flap instantly and closing it when I switch off. The faulty bit was me!

[cass3958]

No problem that is why we are here.
On to the next question.