What was found
ON CLIMB OUT WE ENCOUNTERED ICING AND AFTER TURNING ON THE BOOT THE DEICE TIMER CAUTION ILLUMINATED IN SLOW & FAST. PERFORMED E&A CHECKLIST,BOOTS WORKED IN MANUAL. RETURNED TO FIELD. LANDING UNEVENTFUL. REMOVED FROM SERVICE. CHECKED CDS FOR FAULTS. ICE/RAIN FAULTS ARE UNAVAILABLE DUE TO ICE/RAIN SYS UNAVAILABLE. REMOVED AND REPLACED TMU IAW Q400 AMM TASKS 30-11-01-000-801 AND 400-801. USING ENGINES, C/W FUNCTION TEST OF AIRFRAME PNEUMATIC DEICING SYSTEM IAW Q400 AMM TASK 30-11-00-720-801. FUNCTION TEST GOOD. NO FAULTS POSTED IN CDS. DEICE TIMER CAUTION DID NOT ILLUMINATE. RETURNED TO SERVICE.