LEAR 35 FLT CREW ENCOUNTERS ICING CONDITIONS; ACFT STALLS; FLT CREW REGAINS ACFT CTL AND DIVERTS TO ANOTHER ARPT; LANDS SAFELY.

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WE DEPARTED ON A REPOSITIONING FLT BACK TO BUFFALO; NY. OUR ALT WAS 5000 FT MSL AND WE WERE JUST ON TOP OF A CLOUD LAYER. AS WE PROCEEDED TOWARD OUR DEST THE TOPS ROSE AND WE FOUND OURSELVES IFR WITH ALL ANTI-ICING EQUIP ON AND INDICATING AS SUCH. ATC CLRED OUR FLT TO DSND TO 4000 FT; AT WHICH TIME WE WERE PICKING UP MODERATE RIME ICE. I ADVISED ATC OF THIS AND THEY CLRED OUR FLT TO DSND TO 2300 FT. THE FO WAS FLYING THE ACFT AND I BEGAN TO PREPARE FOR THE APCH PHASE OF THE FLT. WITHOUT WARNING; THE ACFT WENT INTO A STALL AND STARTED TO DSND UNCTLABLY. THE FO RESPONDED IMMEDIATELY WITH FULL THRUST WHICH COULD NOT NEGATE THE STALL SITUATION. WITH THE ACFT SHAKING AND STALLING IT TOOK BOTH OF US AND CRM TO IDENT AIRSPD; CLB OR DSCNT AND KEEP THE ACFT FLYING IN A STALL CONDITION. AFTER MUCH ERRATIC OP WE WERE ABLE TO CLB THE ACFT TO VFR CONDITIONS ON TOP (APPROX 8000 FT MSL) WHERE IT WAS STILL SHAKING AND VERY LOW AIRSPD ALTHOUGH WE WERE STILL AT FULL THRUST. DURING THE WHOLE PROC I BELIEVE I NOTIFIED BUFFALO APCH WE HAD PROBS AND WE WERE ATTEMPTING TO CLB. WHEN WE GOT ON TOP; I THEN ADVISED BUFFALO APCH OF OUR SITUATION AND THE NEED TO DIVERT TO AN ARPT WITH VFR CONDITIONS. AS WE BEGAN TO STABILIZE THE ACFT THE ANGLE OF ATTACK AND AIRSPD BEGAN TO SLOWLY RETURN TO NORMAL INDICATIONS. WE DIVERTED AND BRIEFED FOR A LNDG WITH ICE ON THE ACFT. WE COULD SEE A LARGE ICE ACCUMULATION ON THE NOSE OF THE TIP TANKS AND THE WINDSCREEN WAS STILL TRYING TO CLR. THE ACFT WAS LANDED AT ROCHESTER INTL WITHOUT FURTHER OCCURRENCES. AFTER PARKING; A LARGE AMOUNT OF RIME ICE WAS PRESENT ON THE ACFT. IT WAS DETERMINED BY MAINT THAT THE STABILIZER HEAT HAD FAILED AND THE ACFT ENCOUNTERED A TAIL PLANE ICING STALL. FURTHER INVESTIGATION REVEALED THAT SEALS LOCATED IN THE ELBOW SECTION OF THE BLEED AIR HAD BEEN IMPROPERLY INSTALLED AND HAD FAILED. PRIOR TO THE STALL WE HAD NO INDICATION OF REDUCED AIRSPD; ACFT SHUDDER OR ANGLE OF ATTACK MOVEMENT; THE FIRST INDICATION WE RECEIVED WAS THE SIGNIFICANT BUFFETING AND DSCNT.