As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, HAD A CHEMICAL ODOR IN THE COCKPIT. RETURNED TO DEPARTURE. APU WAS OFF AFTER ENGINE START & NOT USED ON THE GROUND FOR BLEED AIR. THERE WAS NO VISIBLE SMOKE. INSPECTED AND FOUND OIL RESIDUE IN THE APU INLET. REMOVED AND REPLACED THE APU IAW MM 49-10-00. OPS AND LEAK CHECKED GOOD. NO ODOR DETECTED AT THIS TIME.