The city club who had finished seventh in I-League 2011-12 today announced a one season association with the Costa Rican who was the top scorer with 10 goals, totalling 36 goals in 122 games in five seasons of Australian A-League.
United SC hoped that Hernandez's association will help the club clinch the Asian Football Confederation (AFC) Cup in the upcoming season.
Terming this a big decision to move to India, the Costa Rican said: "I feel that there is this huge zest and enthusiasm for football here. I am excited to be part of this excellent team and hope to contribute to the success of the team in the coming season."
Hernandez thus completes the club's three foreigner quota with Martins and defender Bello Rasaq already in their roster.
The club has also roped in ace goalkeeper Subrata Paul and Gouramangi Singh.
The Costa Rican international has also been in the Melbourne Victory, Australian A-League club.
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He has been the recipient of Johnny Warren award for best player in the Australian A-league for 2009-10.
Hernandez has also played in the U-20 World Youth Championship held in Argentina.
He represented the country in the U-23 team at the 2004 Olympics.
Carlos had been capped for the senior national team on 30 occasions, playing for the team during the 2006 FIFA World Cup qualifiers.