Just a shot in case it helps but..Is it new or always done this? Mine needs the aircon to be on for the heater to work

 

I just bought it the ac works but the heat blows cold it's not the duel climate control either I just bought it last week and the owners said the heat worked when the had it but it sat for awhile cause the timing chain started rattling so I got it for cheap because my husband can fix it we already own the tool but no codes are on just no heat only cold blows and mine is a rag top I've done some research it says something about a heater matrix is that minis name for heater core