Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
when I used one with the master cylinder cap on it drew a vacuum and the fluid stopped flowing. So I would say it should be off.I did...not sure if you’re supposed to, but it worked for me.
I have one of their pressure bleeder, uses compressed air to run it(which I had then). Worked well on the Burb brake repairs in 2018, when I replaced both calipers and hoses. Biggest problem was I needed to make a fixture to hold the bottle up into the master cylinder. Made it from baling wire. Cost around $32 IIRC. Made it possible to get the brakes bled by myself, so well worth it.when I used one with the master cylinder cap on it drew a vacuum and the fluid stopped flowing. So I would say it should be off.
Harbour freight is good for the tools you need only once or twice. But then it depends on how you abuse the tools.