How can you have a class a cdl without air break indorsment?

There is no air brake endorsement - if you don't take both the written air brake test, and do your road test in a vehicle equipped with air brakes, you get a restriction barring you from operating an air brake equipped CMV.

But yes, it is possible to have a Class A CDL with a "no air brake" restriction.

The requirements for a Class A CDL are that the vehicle be used on a commercial, for-hire basis, that the Gross Combination Weight Rating be over 26,000 lbs., and that the vehicle in tow (the trailer) have a weight rating of over 10,000 lbs. It doesn't have to be a tractor-trailer. You can road test in something like a Ford F650. The F650 is rated at 26,000 lbs - that in itself does not require a CDL. If you attach an eight ton trailer to it, you now have a vehicle requiring a Class A CDL. You can take your Class A CDL road test in that, and you'll receive two restrictions - "no air brakes" (only applicable to CMVs - you can still drive an air brake vehicle not requiring a CDL), and "no tractor-trailers".