CAPT OF ACR LTT ACFT WITH A PRESSURIZATION PROBLEM DSNDED BELOW ASSIGNED ALT DUE TO MISINTERPRETING A HDG CHANGE FOR AN ALT ASSIGNMENT. IN ADDITION; DID NOT ADHERE TO NEW HDG CLRNC.

Narrative

ON FLT XYZ FROM SYR TO CLE AT FL240; FO LOST XMISSION CAPABILITY WITH HEADSET. WE HAD TO REMOVE HEADSETS TO COMMUNICATE WITH EACH OTHER. SEVERAL MINS LATER; FORWARD DOOR LIGHT MAP 'DOOR' LIGHT ILLUMINATED ALSO RECEIVED 'DOOR' ORAL WARNING. NOTICED PRESSURIZATION FLUCTUATIONS. NOTIFIED ATC THAT WE NEEDED TO DSND TO 10000 FT AS A PRECAUTIONARY MEASURE. REFED QUICK REF HANDBOOK (QRH) FOR FORWARD DOOR LIGHT ILLUMINATED. FOLLOWED THE PROCS PER QRH. HAD FLT ATTENDANT SIT DOWN AND TURNED ON FASTEN SEATBELT SIGN. ATC STATED TO EXPECT DSCNT MOMENTARILY AT THIS TIME; EXPECTING THE DSCNT; ATC NOTIFIED US TO TURN TO 200. WITH THE PROBLEM AT HAND; FLUCTUATION IN PRESSURIZATION; AND LACK OF HEADSETS; CREW'S HEARING WAS IMPAIRED. FLT CREW; EXPECTING THE DSCNT AND MISINTERP OF ATC INSTRUCTIONS; DSNDED TO FL200. ATC ASKED IF WE WERE ENCOUNTERING ANY PROBLEMS. WE ADVISED ATC THAT WE WERE TAKING PRECAUTIONARY MEASURES. ATC INSTRUCTED US TO DSND TO FL180 AND SWITCHED US OVER TO THE NEXT ATC FREQ. ON NEXT; ATC FREQ; WE WERE DSNDED TO 10000 FT WHERE FO VISUALLY CHKED TO MAKE SURE THE DOOR WAS ALIGNED AND PROPERLY SEALED. FO VERIFIED DOOR WAS SEALED AND PROCEEDED TO CLE. DURING THE ENTIRE TIME; WE TOOK THE MOST PRUDENT COURSE OF ACTION TO ENSURE SAFETY OF FLT. RECOMMENDATION: ATC SHOULD REQUIRE FULL READBACK FROM CREW FOR BETTER CLARIFICATION. CREW SHOULD VERIFY BTWN EACH OTHER ON ATC INSTRUCTIONS.