What was found
AT CRUISE, EXCESSIVE SMOKE FILLED THE COCKPIT. APPEARED TO COME THROUGH THE A/C VENTILATION SYS. COCKPIT TEMP SETTING HAD RECENTLY BEEN ADJUSTED TO A WARMER SETTING. TEMP CONTROL RETURNED TO COLDEST SETTING. SMOKE DISSIPATED DURING EMERGENCY DESCENT. RAN ENGINES IAW JRH INDIVIDUALLY WHILE OPERATING PACKS INDIVIDUALLY & TOGETHER. RAN ENGINES TOGETHER WITH PACKS OPERATING. ALL PACKS OPERATED WITH NO EVIDENCE OF SMOKE OR ODOR. INSPECTED ALL 3 PACKS & PACK BAYS. NO DEFECTS NOTED. INSPECTED AVIONICS & CTR ACCESSORY BAYS, NO EVIDENCE OF SMOKE OR DEFECTS. REPLACED BOTH AVIONICS FAN FILTERS & ACCESSORY BAY FAN FILTER. RAN PACKS FOR 2 HRS AT VARIOUS TEMPS & DIFFERENT ISOLATION CONFIGURATIONS, NO DEFECTS,