Air for tires on Type A

I am inclinded to go with the 135PSI answer.
Suggestion blead it down Remove the coupler. Install a quarter turn air valve (Get those any big box home improvement store and most hardwares) and that way you can cut off air to the coupler. Then you can push in lock down and apply pressure by opening the valve.

IF in fact it's frozen While it's off the rig. A small rod like tool into the center and wack it. NOTE as someone said 5-10 bucks to replace.

If it’s never been used it’s probably frozen. They are easily replaced for $5.

I have no trouble connecting either of my compressors with one set at 150 PSI and one at 175 PSI. The trick is to keep them lubricated inside and outside so they will not corrode and siege. Squirt some penetrating oil inside and around the outside sleeve and try rotating the sleeve. Once it is loosen a good firm push on the air chuck into the coupler should make connection.

If they sit for a long time without use they tend to freeze.

Does your hose have the correct adapter/connector to plug into the bus?

I'd guess it's not frozen, but instead, you're trying to push that bayonet into the fitting against the 115-135psi system air pressure. To see, shut off your engine, bleed down the air tanks with your brakes and drain valves and then try the bayonet. If it goes in, you've identified your problem. On my Bus, I put a 1/4 turn ball valve just behind the coach fitting so I can connect my (2) air lines with ease. I understand the latest Tiffin's have this valve factory installed so this problem has gone away.

You could try squirting it with some penetrating oil...that might loosen it up.