Having trouble with A/C stuck on defrost?

Recently when I was accelerating my A/C would switch to defrost and then back to vents when taking my foot off the accelerator, until it finally stuck on defrost.

So, I purchased a new check valve and a small section of 1/8 tubing (Dorman part 47417) which is only 3ft sadly, I pulled the cowling off the got the grommet out, but unfortunately, it came out of the connector inside the car and I'm unable to feed that line back down through the dash without removing the passenger airbag to reach it and feed it back down to the connector.

So, I have two questions, the first being what size vacuum hose would you use to run an entirely new line through the firewall if you were to replace it (right now I just have that section of Dorman hose and the original hose I pulled out of the grommet and then jammed a piece of tubing over the grommet end to hold it snug, I can't find anything close to that size standard anywhere, and most Taurus' those lines are rotted, so a junkyard part would be probably just as bad)?

And the second question is, what is the safest method to go about removing the passenger airbag in the car listed above?

I'm familiar with the power one of those has, so my assumption is the standard disconnect the battery, wrap the terminals in electric tape for extra safety and turn the key on for 10-20 minutes to discharge the capacitors and then let it sit overnight (and of course, safety glasses, nitrile gloves, etc.). I want to approach it as safely as possible so there's no setting off of the airbag, as I don't have the almost $1,000.00 I'm being quoted for that job.

Thanks for any advice you can offer!