As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB AT FL 200 WITH WING ANTI-ICE ON SELECTED CABIN BEGAN TO CLIMB AND DESCEND RAPIDLY. FLIGHT DESCENDED TO FL 100. NO MENTION OF OXYGEN MASKS BEING DEPLOYED. FLIGHT DIVERTED TO PHL AND LANDED WITHOUT INCIDENT. MAINT REPLACED CABIN PRESS CONTROLLER AND OUTFLOW VALVE. ALSO, REPLACED ICE PROTECT THERMOSTAT AND ANTICIPATOR. OPERATION CHECKS GOOD.