Adapter for Shop Air-to-Manifold Gauges

[manimalism]

I need to pressure test a sealed system to find a leak. Problem is, I can't find the correct adapter to connect shop air (or a bottle of nitrogen) to my manifold gauges. The former is a typical 3/8-in by 18tpi male NPT fitting; the latter uses male ACME thread. (Picture the threaded connector on a bottle of r124 refrigerant here.)

I asked two different AC techs I happened upon at a Home Depot parking lot this question, but neither had a clue.

Please post a link to where I can buy this sort of adapter, or the two fittings so I can make my own.

[machinist]

Hi, welcome to the forum! It sounds like you're trying to connect shop air or a nitrogen tank with a 3/8 inch NPT fitting to your manifold gauges, but you're having trouble finding the right adapter. Most HVAC manifold gauges actually use 1/4 inch SAE flare connections, not ACME threads, so in most cases, what you really need is a 3/8 inch NPT to 1/4 inch SAE flare adapter. These are pretty common and can be found online through HVAC suppliers like TruTech Tools, Century Tool, or even on Amazon or eBay. If you can't find a single adapter that does the job, you can piece it together using a 3/8 inch NPT to 1/4 inch NPT plumbing fitting, followed by a 1/4 inch NPT to 1/4 inch SAE flare adapter.

That said, since you mentioned your manifold uses male ACME threads, it's possible you're working with an automotive A/C manifold, especially if it's designed for R-134a systems. These setups often use 1/2 inch ACME fittings, which are different from the standard SAE flare connections used in most HVAC tools. If that's the case, then you'd need a 3/8 inch NPT to 1/2 inch ACME female adapter instead.

To be sure you're getting the right part, it's worth taking a close look at the threads on your manifold. If it turns out to be 1/4 inch SAE flare, you're in good shape since adapters for that setup are easy to find. But if it really is 1/2 inch ACME, you'll just need to track down the less common fitting. Once you’ve confirmed the thread type, getting the right adapter should be straightforward and will let you pressure test your system without any issues.