i just started looking at the problem. but need help??? maybe a/c or heater or seal???

a/c not bowing cold? i am thinking just trying to refill refrigerant? but i have a question
about the heater. so when heater is on it don't really blow warm or it seems like it
takes a while to heat up. and the front windshield fogs little bit. now when i put the
heater on defrost. it fogs up window allot bad. plus a little smell and little residue. so i
goggled it and i got heater core to come up. so i checked that out and i don't have fluid
on inside passenger or driver side like it would be leaking. no fluid. an then i had the
two hoses going into core checked both very hot. and car is not over heating. i do
have a engine seal leak, could that be the problem maybe?? so i wanted to know
where i might check next?? or a list of things i could check?? before bypassing core if
that is what i need to do. any help or direction would be appreciated. and please let me
know your experience working on cars. may you have a blessed day. and thank you if
decide to help in my quest.