1984 coleman 7680c856 standing pilot light. Burner runs reaching operating temp blower fan kicks on for 90 secs then cycles off for 2 1/2 minutes. Then back on for 90 secs while burner runs the entire time.replaced with new gas valve,fan switch,limit switch.flame on burner appears blue. Acts like not building enough heat to keep fan on. This is in a mobile home.