Why does the amount of tax I owe increase when I enter Expenses on Scheduel F?

[Critter]

FIRST ... you MUST report all income & expenses you have on the Sch F  no matter what the refund/balance due meter says.

Next, reduced income can reduce some credits.  Since you have the downloaded version switch to the FORMS mode and look at the form 1040  before & after you enter expenses   to see how those entries are effecting the return.