Max has explained almost the things reagrding to what AT mean.
Just some more information:
When you check from the part book, there are normally 2 part No. for one controller: One is for the new one and the other is for the AT one. When you ask for the price : the AT one is always cheaper ~50% of the new one.
If you are the dealer or agency, when you would prefer to order the AT one: first you have to pay 100% value as same as the value of the new one then you have to send back to defective one to the manufaturer (Linde, Jung, Still,...). After receipt of the defective one the manaufacturer will check and inform you if it is repairable or not. If yes, they will pay back 50% value to you if not you have no way to buy the new one. Therefore, AT is as same as Exchange in English.

In case you are not the dealer you also contact to the dealer or supplier they can help you on this matter.

Rgds
Nuna