According to this URL the limits are below but I don't think it is accurate as my friend sends more than that each month.
At any of our Western Union stores or participating agent locations, you will be able to send up to 3,588,000 ARS per money transaction and up to 3,588,000 ARS total per month.
You can also send a total of 3,744,000 ARS per calendar year. If you want to send more than 3,744,000 ARS within a calendar year, you will need to provide additional documents to be able to do so.
Find the answers to many of your questions here. How to send money from Argentina, how to pick-up money at agent location and others.
www.westernunion.com