What was found
CREW REPORTED UPON CALLING AN ARRIVAL FOR FLC70 THAT THEY RETURNED TO KBWI FOR MAINTENANCE DUE TO AIRCRAFT OVER-PRESSURIZATION AND A STRANGE ODOR AND POSSIBLE FUMES. ATC DECLARED AN EMERGENCY ON BEHALF OF THE CREW. AFTER DESCENDING TO 10,000FT AND DEPRESSURIZING, ODOR DISSIPATED. MAINTENANCE HAS BEEN NOTIFIED. DURING TROUBLESHOOTING NO DEFECT HAS BEEN FOUND. AFTER TALKING TO THE PILOT THEY WERE AT 20,000 FT WITH MAX DIFFERENTIAL OF 6.4. NO OVERPRESSURE SITUATION. SAID THEY HAD A RUBBER BURNING SMELL. FOUND AUX AC CIRCUIT BREAKER POPPED, RESET AND RAN AUX AC WITH NO ISSUE. MEL'D PRESSURIZATION AND RETURNED BACK TO HOME BASE OF KACY FOR CONTINUED TROUBLESHOOTING.