Troubleshooting hideways is very similar to electrical issues. Start at the front of the system to see if you have vacuum at the actuators, both red and green hoses in the respective on/off positions of the switch. If not, work your way back to find where it's being lost. If you're not getting vac to the actuators, check that you're getting vac into the valve on the can from the switch. If not, check that vac is getting to the switch from the engine, and so on.
It shouldn't take but a few seconds to get the system vacuumized (is that even a word?). If pulling very low vacuum at idle, give it some RPMs.
You can check the actuators by pulling a vacuum on them. It should move the rod (test both directions) without any leakdown. There's a pretty decent chance they've gone bad. If you think the large vac can is possibly bad, you can disable it from the system to eliminate that as a possibility. It's only used to hold reserve vacuum for when the engine is turned off, but can be a source of a vacuum leak.
Also, Ive had a brand new, out of the box OER RS headlight switch that was bad. Ive also seen OER valves (one that mounts on the reserve can) that were made backwards internally. R hose to R terminal and G to G, they would close when the lights were turned on and vice-versa.