B200 FLT CREW EXPERIENCED A L BLEED AIR FAILURE AND SUBSEQUENT PRESSURIZATION ISSUES. UPON INITIATING AN AGGRESSIVE DESCENT THEY QUESTION WHETHER THEY HAD RECEIVED THE CLEARANCE TO DESCEND OR IF THEIR ACTIONS WERE PREMATURE.

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FLT WAS BEING OPERATED UNDER FAR PART 91 WITH 2 PLTS AND 6 PAX. AS THE ACFT WAS LEVELING AT THE FINAL CRUISE ALT OF FL270; THE MASTER WARNING LIGHT ILLUMINATED ALONG WITH THE L BLEED AIR FAIL LIGHT ON THE ANNUNCIATOR PANEL. THE CABIN ALT INDICATED 5000 FT. PRIOR TO PLACING THE L BLEED AIR VALVE IN THE 'ENVIRONMENTAL OFF' POS; IN ACCORDANCE WITH THE CHKLIST; THE PLTS DISCUSSED THE POSSIBLE NEED TO DSND IF THE REMAINING BLEED AIR WAS INSUFFICIENT TO MAINTAIN CABIN PRESSURIZATION. WHEN THE L BLEED AIR VALVE WAS CLOSED; THE COPLT NOTICED AN IMMEDIATE 4000 FPM CLB ON THE CABIN VERT SPD INDICATOR. THE PLTS REQUESTED AN IMMEDIATE DSCNT FROM ZAU AND WERE CLRED TO FL240. THE PIC STARTED A 3000 FPM DSCNT TO FL240 AND THE COPLT REQUESTED A FURTHER DSCNT. ZAU ISSUED A FREQ CHANGE TO ANOTHER ZAU CTLR AND THE PIC THOUGHT HE ALSO CLRED THE ACFT TO FL190. THE PIC; BELIEVING THE ACFT WAS CLRED TO FL190; CONTINUED THE DSCNT. THE COPLT CHKED IN WITH ZAU PASSING FL237 DSNDING TO FL190. THE NEW CTLR DID NOT INDICATE THAT THE ACFT WAS NOT CLRED TO FL190; BUT DID ASK THE COPLT TO CONFIRM DSNDING TO FL190. THE COPLT CONFIRMED THE ACFT WAS IN THE DSCNT TO FL190 AND DUE TO A PRESSURIZATION ISSUE A FURTHER DSCNT WAS NEEDED. THE CTLR THEN ISSUED A CLRNC FOR A DSCNT TO 14000 FT AND A 20 DEG L HDG FOR THE DSCNT. PASSING THROUGH APPROX 16000 FT; THE CABIN ALT RATE OF CLB SLOWED AND EVENTUALLY STARTED TO DSND. THE ACFT LEVELED OFF AT 14000 FT; THE CABIN ALT DSNDED TO AND REMAINED STEADY AT 9000 FT. AT THIS POINT THE PLTS ASKED FOR A CLB TO 15000 FT IN ORDER TO BE CORRECT FOR DIRECTION OF FLT. THE CABIN ALT REMAINED STEADY AT 10000 FT FOR THE REMAINDER OF THE FLT AND FLT PROCEEDED TO THE DEST UNEVENTFULLY.