I am confused by your description.
Usually a workorder is unique per row but this appears that you can have multiple rows per workorder.
Also not sure how your GRopup A, B, C is functioning. I can see B and C being a sub group of A but B cannot be a subgroup of C or vice-versa? Are you just using the word 'group' here and these are not actual groups in Crystal?
The best solution would be to do this outside of crystal using a view or stored procedure but if you are limited to working with crystal and B and C are not really a group but a way of identifying a row withing a real group of A then try this.
Use the select statment of
{WOITEMS.TOTALSALE}>0
Group on {table.WORKorderNBR} field
you need two formulas not just one like you had.
Create a formula called "GroupB" as:
If {DISP.NAME}={TECH.NAME} THEN 1 Else 0
Create a formula called "GroupC" as :
If {DISP.NAME}<>{TECH.NAME} THEN 1 Else 0
Now use the Insert Summary Function on @GroupB field as a SUM reset on grouplevel1.
Repeat @GroupC field set as a SUM on grouplevel1.
Go into Select Expert.
Click on Show Formula
CLick ont he toggle for "Group Selection"
Click on Formula Editor.
Expand the Reports Fields
Double click on the field with the Sigma sign as SUM of @GroupB and add >0 in the formula
Do the same for the Sum of GroupC
Save and Close.
Will be something like:
and
When you run the report you will still see items appear in the group tree that are excluded based on this selection but they will not appear in the body of the report.