The Air Grabber on my ‘70 GTX will sometimes open only partially and sometimes not at all. And when it does move it does so verrrry slowly. I replaced the actuator a few years ago but I realize reproduction quality isn’t always great. I did try testing it with a vacuum pump and could get it to work so if I was using the pump correctly then apparently the actuator is alright. I also pulled the fuse in the accessory block and checked it.

So what is the most likely culprit? Before I go digging around under the dash for the switch or dismantling the vacuum can I was hoping to get some experienced voice to point me in the most likely direction.

Thanks.

Maybe a pinhole leak in the can? See if it can hold a vacuum.

Take the hoses off right at back of switch and use your pump to try to raise and lower it. if all goes well then it's the switch. If not break it down into sections to test at the different points.
Ron

That. The switch is just plastic that gets brittle and it's easy to break the nipples and start a leak.

At one time I rigged up an industrial control type vacuum switch to use. It worked well. I left the factory switch in the dash for looks (always up) and put the replacement under the edge of the dash.

Oh goody, wiggling around on my back to get under the dash! Just what these antique bones were hoping to avoid!🤣.
But thanks for the replies, it hadn’t occurred to me to try the vacuum pump at the switch. Probably more likely the switch than the canister.