1996 Grande Marquis V8 The heater is always on even when you turn on AC on 1996 Mercury Grand Marquis

A few months ago the system started to make a poping noise inside the dash like one of the control functions was in a stuck position. Noise stopped now AC will not work.

1 answer
Probably a blend door actuator has failed. When they go bad....the vent will not switch from the heat to a/c....Different HVAC lines. Need to have inspection done to see if this is the cause but I suspect it is.