2003 Chevy Impala climate control problems

We have a 2003 Chevy Impala that the a/c blows intermittently. When it stops blowing the control panel freezes. Also sometimes when this is happening, the dash “cruise” light comes on, but the cruise control is frozen also. We have replaced the blower motor, the blower motor module & the blower control register. It still doesn’t work. The GM dealer is stumped & the Service Manager is no longer returning our calls. Can anybody help??? Thanks