Air carrier Captain reported a fumes event during climb was caused by the left pack failure and led the flight crew to return to the departure airport.

Narrative

Normal takeoff on Runway XX; leading to the ZZZZZ Departure. Reaching 8;000 we turned to ZZZZZ. After passing through 14;000 feet and abeam the volcano we had smoke and fumes in the flight deck. Started by a strong burning smell followed by a light haze of smoke. I called for masks on. After we both had our masks on I selected vertical speed zero to stop the climb. I instructed the FO to work the radios; fly the plane; and to request priority handling. He then initiated the return to the airport. I began running the smoke/fumes/odor checklist QRC/QRH. As a troubleshooting step in QRH the right pack was turned off and was to remain off since the smoke and smell was gone. During this the left pack (which was on a recall MEL) had failed completely. This then began a gradual depressurization around 7;000 feet. We then reduced the rate of descent since cabin rate and aircraft rate were the same. Prior to landing we completed the overweight landing checklist (154;100 lb. landing weight) and before landing checklist. I then resumed the radios for landing. After landing we taxied normally to the gate with emergency vehicles following. No further incident or recurrence of the smoke/fumes.Cause: Primary cause was the left pack failure introducing smoke and fumes as it began to fail.