Before Season 8, Carl and Frank used to be close. He once mentioned having wanted to ask Frank to let their mother live with him as a favor in helping him through college. However, Harriette put her foot down and reminded him of Frank's frugality.
Frank comes for a visit in his clown garb from his job in the Sullivan Family Circus. Although he and Harriette is happy to see each other, Carl wasn't happy to see him. Out of reluctance, he arrests Frank for fraud charges which leads to a fight between the two.
When Frank accuses him of arresting him out of spite for skipping their father's funeral, Carl furiously pointed out that he should've been there for their mother because she was going through a tough time. He also tells Frank that their father's death bothered him and their older brothers as well, but they were all there to lend Estelle support though the hard times. Harriette finally convinces Carl to hear him out. Frank finally explains that their father's death affected him deeply and couldn't be there due to a previous fight the two had. He tried to call Carl to about it and apologize. When he didn't answer, Frank was convinced that Carl hated him and gave up after a while. Carl mentions that he would've understood if Frank came to him in person to tell him, instead of calling him. Frank explained what happened to his previous job at the restaurant as a manager, years earlier. Things went well for him until the restaurant lost money and closed, causing his last paycheck to bounce.
Before Carl could say anything, Harriette tells him that it happened before with their friends and family. She also mentions that he shouldn't criticize them about it since they know what it's like to be in Frank's shoes. Carl asked Frank if he was looking for a job to make money to pay off his debts. Frank tells him that he already has one as a clown in in the Sullivan Family Circus which pays him very well and he has started paying back his debts. Carl realizes that his family does come first over his job and decides not to arrest him. Then, he loans his brother the money he needs to pay off the last of his debts and rebuild a long forgotten close relationship between them. This decision makes Harriette and Frank real happy with him.