I want to recharge the refrigerant in my auto air conditioner. I've assembled all the necessary tools except for one item. My vacuum pump is outfitted with a 3/4" female NPT fitting and the discharge tube from the gauge set is a R134a female fitting. I plan on machining an adapter to get the 2 fittings connected to each other.
But I can't figure out what the thread size is on the R134a. Please enlighten me!
Don't reinvent the wheel by machining the fittings, it's silly to waste $100 to $200 of your time on a $5 part - you only do that when it's made out of pure Unobtanium... Go to any refrigeration supply house or search online.
They have in-stock adapters to go from NPT pipe thread to 1/4" SAE Flare (HVAC and Refrigeration charging hose fittings) 3/8" SAE Flare (manifold to vacuum pump hose connection) and 1/2" Acme Flare (R-134a Automotive Manifold hose fittings)
Your vacuum pump should have 1/4" SAE Flare and 3/8" SAE Flare fittings if it was made for refrigeration work - you connect the manifold hose with the 3/8 fitting, and can attach the micron vacuum gauge to the 1/4" to monitor your progress.
(If the system under vacuum has an extra service port, connect the vacuum gauge sensor directly to it. That way you can isolate the system with a ball valve and shut off the vacuum pump, and monitor the vacuum levels for leaks and/or trapped moisture still evaporating from the refrigeration oil.
If you are adapting an industrial vacuum pump, you'll have to bushing down from 3/4" NPT down to the threads needed for the adapter.
What the (heck) are you talking about? They don't have to be "government approved".
Unless they've made some serious changes since I took and passed the test, there are no approvals processes or "lists of approved machinery..." You just have to use procedures to reduce accidental or incidental release of CFC's and HCFC's as much as possible. And deliberate release is instant trouble.
A car using R-134a is running an HFC. No chlorine.
The EPA via the Clean Air Act regulates what fittings can be used with what refrigerants. Not the marketplace, not engineering standards, not the convenience or expedience of you or me or the OP. I don't agree with the despotism of the government, I'm just warning you. The law makes us all criminals, even for things like cutting metal. The tender mercies of the bureaucrats decide who is punished and who is given lenience.
The service fittings permanently installed on the vehicle or stationary system, yes. If you do a conversion from R12 to R134a or another refrigerant you have to change the fittings to the proper style to avoid accidentally mixing refrigerants.
But not an adapter made so you can hook up your service manifold hoses to the car or refrigerator being serviced, or hook up the hose from your vacuum pump to your service manifold. They may be stupid MF's working for the government, but they ain't THAT stupid.
It's the mouth breathing politicians who wrote the impossible to follow laws the bureaucrats are trying to (selectively) enforce who
*are* that stupid. Which is why politicians are like diapers - they need to be changed often, and for the same reasons.
The EPA holds that if certain fittings are required, then adapters to circumvent them are not permitted, since that defeats the very purpose of the fittings, namely to make impossible the mixing or confusing of refrigerants. While the utility of adapters is obvious, you're supposed to have a separate set of gages and hoses for each refrigerant. That's the governmental logic: intelligent economizing must give way to backstopping presumed stupidity.
As Uncle Al sez, environmentalism is expensive, shoddy, and deadly.
So ..leave those fittings for R134a on your hoses because they are not adaptors, but a permanent conversion to make an obsolete tool usable. If it became necessary to permanently convert the tool to R12, do so at that time.