In reply to Tom Hsiung.

The documentation for the ESTIMATE statement explains the syntax. The ESTIMATE statement tests whether any linear combination of the parameters is equal to 0. In this case, we have a class variables with two levels Site='A' and Site='B'. Call C1 the parameter for the 'A' site and C2 the parameter for the 'B' site. Then the hypothesis that the parameters are equal is
C1 = C2
which you can rewrite as
(+1)*C1 + (-1)*C2 = 0
The values +1 and -1 in that equation are the values that you should use in the ESTIMATE statement. (You could also use -1 and +1.)