iRule to redirect based on availability

Hi, I agree with @nitass comments. You need to verify 1st Pool_C status. I guess, it require two iRule to check the connection. Status of Pool C. If it is up then it traffic will go to 2nd iRule.

Rule 1(make 1st iRule)

when HTTP_REQUEST {
     if { [active_members pool_c] < 1 } {
        HTTP::redirect http://failoverurl
         return
             }
         }

Rule 2. Redirect traffic based on the condition.

     when HTTP_REQUEST {
            set uri [string tolower [HTTP::path]]
            switch -glob $uri {
            "/A/" { pool A }
            "/B/" { pool B }
            "/C/" { pool C }
                     }
                }

Hope it will work..