the gauges? does ur rad cap get warm? cuz to me would seem thats the coolant while in the heatercore is not hot enuff to present out heat. so it could be a prob even in ur coolant procedure, or perhaps a thing similar to a stuck closed tstat.. http://rvheaterblowingcoldair50494.blogdon.net/a-secret-weapon-for-rv-heater-blowing-cold-air-22184549