The System Coupling systems do direct coupled-field analyses using the coupled-field (22x) elements. So, yes if you used direct coupling with the 22x elements, you could create 1 input file. However, there are disadvantages (and some advantages) of using the direct coupled-field elements for thermal-structural analysis. Most users prefer using the sequential coupled-field approach (see the MAPDL Coupled-Field Analysis Guide) for thermal-structural analysis. I assumed that you were using the sequential approach.
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