Defroster doesn't start AC

My AC works great and the defroster does blow. But, when I turn on the defroster the AC does not kick on. Anyone seen this before? Would this likely be the dash switch or some relay/module?

1998/Jimmy SLT

just one more thing, Joe

Does the A/C come on when you have the control module set to A/C? If the A/C compressor kicks in and works in "normal A/C" then it could be the control switch. The switch sends a "request" for A/C signal to the Computer along the same wire. If the A/C compressor comes on in "normal" mode and not in "defrost" then it could be the control switch.
JMHO :2cents:

yes the compressor does kick in on A/C. I figure it's the control switch. I just want to see if anyone has had this problem and if the control switch fixed it.

Thanks