As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORT FINAL, STARTED APU FOR GROUND COOLING PAX COMFORT. AS SOON AS WE STARTED THE APU WE GOT WINDSHIELD HEAT INOP L AND DC GEN OFF L CAS MESSAGES DISPLAYED. CORRECTIVE ACTION: REPLACED L/H GCU WITH REPAIRED GCU IAW CE-680AS AMM 24-30-45. OPERATIONAL CHECK SATISFACTORY.