In our office there was a discussion about ambient temp.
Usually it is 70 Deg F. But an engineer suggested to put 40 deg F since at some time though out the year , ambient air gets to 40 deg F and the there will be a larger difference with the Operating (130 Deg F ) temp.

Should we do that ? or , should we define a separate new temp into load cases and insert 40 deg F into it?

It depend on the precision of the analysis. Being close enough, you mai assign 40f as ambient. This will require less load cases. If you want more precision you can use 70f as ambient and define 40f as min temp. The point is that in Caesar the ambient temp is in fact the installation temperature (0 exp state). The first option will result in a more conservative design.