Identify this canister???

[pats71]

I was working on my 71' Roadrunner tonight and I sat here scratching my head over this canister. I'm guessing this is a vacuum canister for something. The car was built in california. Problem is my car is an original 4 speed with manual HD drum brakes. So what the heck would this thing be for. It is located under the battery tray. I know the that the master cylinder in the pic is not original. That's cause I've got the original in a box while this replacement is used just to give the car braking power.

[quapman]

Your car has A/C and that's a vacuum amplifier for the water valve. Someone here might have a pic of the hose system from the service manual.

[72RoadRunnerGTX]

Technically it's a vacuum reservoir, it provides a more consistent level of vacuum for the all the A/C controls regardless of fluctuations at the intake manifold during engine operation. I only correct the term because in later years there is another device that was called a vacuum amplifier used for emission control systems. The same basic reservoir was used for other systems as well. air grabber, Dodge/Chrysler headlamp doors to name a few. The mounting brackets and nipple sizes varied some.
It seems the more actuators/controls involved in the A/C system determined the need for a reservoir. In 72' the water valve was cable controlled and did not use a vacuum reservoir for the A/C, even with basically the same heater/AC box, the vacuum take-off is connected directly to the intake manifold.

See them offered on e-bay all time as "Air Grabber can", commonly have the wrong brackets however.

here's the same can with a two bracket configuration, headlamp door system I believe.

[71Runner]

So 72RoadRunnerGTX, these AC cans are swappable with the AirGrabber vac can? The only reason I ask is I have AG issues, and was gling to swap out the can b4 swapping out the actuator mounted on the hood. Thanks.

[72RoadRunnerGTX]

The only difference between the reservoir pictured above for the A/C and the one used for the A/G is the bracket is shaped to fit the contour of the inner fender under the battery box. If carful, brackets can be swapped; small tabs tend to break off however. The reservoir is a pretty simple device, empty sealed can with two nipples, one has a check valve. The nipple with the check valve (un-marked and off to one side of the center) needs to go to the vacuum source (manifold fitting). The other nipple is located directly in the middle and identified with a green paint dot connects to the center position of the switch with a green striped hose. If there are no leaks in the A/G system, it provides enough vacuum reserve to open and close the A/G two or three times with the key on and motor just turned off.

As with any vacuum controlled devices/systems, leaks are the main source of problems. A hand-held vacuum pump is the best tool to locate any leaks. The A/G switch tends to be the likely spot for leaks. Make sure you have the solenoid valve plumed correctly, on the A/G up line, and functional as it is intended to be a leak when not energized(key-off).