Where do the Heat / AC controls get vacuum

[dspur]

Dumb question I know, but all of this was out of my 69 Bee when I purchased it Original air rebuilt the heat/ac box some time back, and I have been sourcing other parts, having the vacuum switch rebuilt etc. All is vacuum operated but for the life of me I don't know where that vacuum comes from, can't see anything where it would connect. I am thinking I am still missing some part, vacuum line, etc.? Photo of the restored box for illustration.

 

[davek]

this might help 68-70 B-body factory a/c vacuum line routing

 

[davek]

1968 Coronet 500 Project

Yea, the upper and lower portion which is suppose to match the interior trim. I still haven't decided if I am going to paint mine black or not. Ah. No I shot mine orange to bring the outside color inside. The all black inside was too much for me.

www.forbbodiesonly.com

 

[F4R/T]

You should have a port off of the manifold that usually has power brakes and a little port coming off. It threads in the driver side rear of the manifold, then a little vac line runs thru the fire wall. I can’t recall exactly where it goes once it gets into the cabin.

 

[dspur]

You should have a port off of the manifold that usually has power brakes and a little port coming off. It threads in the driver side rear of the manifold, then a little vac line runs thru the fire wall. I can’t recall exactly where it goes once it gets into the cabin.

Thanks, I will look for both I do not have power brakes. I do have power steering tho. 69 Bee with factory air and factory 4 speed.

 

[Daytrepper]

There is a vacuum harness that goes to all of the actuators, then up to the back of the mode switch on the dash.

As far as the supply, depending on your setup; I ran a line for mine off of the carburetor full time vacuum port. Routed it along the intake and then to the vacuum reservoir under the battery, then back across the firewall with the engine bay harness to the pass thru next to the water valve on the firewall. I added a vacuum reservoir under the battery (same as would be on a later B body) due to the cam in the engine. That line will connect to the little manifold where all the other lines connect at the switch.

 

[dspur]

I will look at my setup. I have everything other than the supply line, but hopefully can figure out where it goes at each end. thx

 

[Daytrepper]

I will look at my setup. I have everything other than the supply line, but hopefully can figure out where it goes at each end. thx

Just need a good vacuum supply from the engine. If going off the carb, make sure its the full time vacuum port. If going off a manifold vacuum tree, no sweat. If you don't have the vacuum reservoir under the battery they added at the factory later, (70 ish?) it's a good idea. Especially if you don't have a stock engine. That will allow the heater box to operate quickly. I've got a relatively aggressive cam in mine so vacuum at lower RPMS is a problem. Heater box is slow to switch modes without the reservoir. Adding the reservoir helped quite a bit, but still a bit slow at low RPMS.

 

[WileERobby]

Do you have a FSM ?

 

[dspur]

Just need a good vacuum supply from the engine. If going off the carb, make sure its the full time vacuum port. If going off a manifold vacuum tree, no sweat. If you don't have the vacuum reservoir under the battery they added at the factory later, (70 ish?) it's a good idea. Especially if you don't have a stock engine. That will allow the heater box to operate quickly. I've got a relatively aggressive cam in mine so vacuum at lower RPMS is a problem. Heater box is slow to switch modes without the reservoir. Adding the reservoir helped quite a bit, but still a bit slow at low RPMS.

Pretty much stock, rebuilt but stock as far as I can tell. Where does the vacuum connect or the heat/ac box ?

 

[dspur]

Do you have a FSM ?

What is that? (I am heat ac systems uneducated and will probably feel dumb when you answer).

 

[70 sublime]

FSM factory service manual

 

[pa383mopar]

The main vacuum for the system runs via vacuum line from a fitting on the left rear of the intake manifold directly to a port on the A/C switch in the dash. The FSM has lots of diagrams to illustrate the vacuum line routing. Here’s an example from my ‘67 manual, but there are differences in the A/C switches from 67 to 69, so be sure to get the correct info for your car. The red box shows the vacuum source on the switch.

 

[dspur]

FSM factory service manual

I knew I would feel dumb. Yes I have that. Not sure I got the answers I was looking for but I’ll review it again. Thank you!

 

[dspur]

The main vacuum for the system runs via vacuum line from a fitting on the left rear of the intake manifold directly to a port on the A/C switch in the dash. The FSM has lots of diagrams to illustrate the vacuum line routing. Here’s an example from my ‘67 manual, but there are differences in the A/C switches from 67 to 69, so be sure to get the correct info for your car. The red box shows the vacuum source on the switch.

View attachment 1520839

Great. Thank you. I’ll re-review the manual.

 

[pa383mopar]

I think your main issue is that you do not have the vacuum harness attached to your heater box (as stated in post #6). That harness has vacuum lines that attach to each diaphragm on the box and runs to the A/C switch on the dash and provides the vacuum line that would run to the intake manifold. See the harness in the picture below with the connector for the A/C switch.

 

[Daytrepper]

Pretty much stock, rebuilt but stock as far as I can tell. Where does the vacuum connect or the heat/ac box ?

Are you talking the vacuum supply from the engine? That connects to the back of the dash switch, into the little vacuum manifold that holds all the lines together coming from the heater box. Run a line from a full time vacuum port on the carburetor base or the vacuum hose tree on the intake manifold if it has one.

If you are completely unable to figure out where your hoses go on the box itself, you can figure it out with the dash switch and a vacuum pump on the work bench. The hose harness that goes with the heater box somewhat gives you some "clues" based on the length of the lines, and the color stripe on the hoses (if you have an original set). Yellow striped hoses retract the particular vacuum pot and the red hoses extend them (yellow connects on back of vacuum pot, red on front). With a vacuum pump connected you can bench test the box and connect all the hoses and use the switch to set the different modes, and make sure they are correctly hooked up; IE make sure defrost pots actuate when you hit defrost, vent pots actuate when you hit A/C, etc. Also make sure they retract for the ones with both hoses when you change the modes.

 

[dspur]

Excellent. I will find that and bench test each with vacuum. I have the original lines, less the one that goes through the firewall to the engine. I guess that was throwing me off and I didn’t realize there was a port on the switch. Thanks much.

 

[Daytrepper]

Excellent. I will find that and bench test each with vacuum. I have the original lines, less the one that goes through the firewall to the engine. I guess that was throwing me off and I didn’t realize there was a port on the switch. Thanks much.

NP; the supply is part of the vacuum harness, it should be a solid black line. The rest to the heater box will all have stripes. It all plugs in to the manifold on back of the switch.

 

[Daytrepper]

for reference;