Well. My air conditioners (Both the 13.5 KBTU and the 1500KBTU) draw 13.5 amps normally.. HOWEVER if the condenser coils get a bit gunked up that can increase.. to like 21 amps on the 13,500 BTU one about a month ago.. I cleaned it and circuit breakers stopped tripping.
Also as others have said a 50' standard extension cord is not going to cut it.. You have two choices here
ONE: Both Sears and K-mart sell a very nice 12ga cord with a push button on the outlet end,, You must push to insert/remove a plug.. Other stores (Lowes, Home Depot, Mennards, And even Ollies Bargains) sell (Sometimes in the case of Ollies) 12ga cords with standard outlets. This might work
Better, use your 30 amp extension cords to the greatest extent possible and the shortest 12ga you can use.
I have multiple 12ga cords here, One is a 40 footer cut into 1/3 2/3 lengths, This I normally use for ONE air conditioner where I need it.
The other is 100' (Sears/K-mart with push button)
The short one from Ollies (The 1/3 part) has 20 amp plug and 15/20 outelt, the longer section 15 plug and combo outlet. (I used the 15 amp outlet to make an adapter I use here in the inside)
Home is where I park it!