rear heater fan won't turn off

My rear heater fan sometimes stays on when the key is turned off and I cannot get it to quit running. Does the same at times when the Air conditioning is on. Any Ideas?? 1999 Chev Suburban 1500.
Chev Suburban 1500

i would suppose the switch is bad, but i dont think power should still be coming to it at all when the ignition is off unless its on the acc position. i guess that would mean the ignition switch is letting it thru?

My rear heater fan sometimes stays on when the key is turned off and I cannot get it to quit running. Does the same at times when the Air conditioning is on. Any Ideas?? 1999 Chev Suburban 1500.
Chev Suburban 1500

You should have 3 rear blower relays in the rear of the vehicle. Replace the one that controls the speed it is stuck on. Low, medium or high. To the best of my recollection, they are on a junction block on in the right rear quarter panel area.