Mine is a 1997 Blazer 4x4. I can turn off key, take key out and radio and other accessories are off, heater is still running. I've had dead batteries because the heater fan does not turn off. Only the heater can run with the key out of the ignition switch. Any experiences? Is it the key switch or the heater relay or who knows?

 

my thought would be relay stuck

 

ive seen this a couple times on the fullsized trucks. both times its been the blower motor resistor. most the times those go out you usually lose a speed or two but have seem them cause the vehicle to keep the fan on

 

I should refine exactly what happens. I can control the fan speed with the key off. I have to turn off the heater/AC or the fan will run, unless I just turn the fan down to off.

 

take a look in the fuse panel for a relay marked HTR

 

Turns out it was the ignition switch. Pretty easy to do, but you need a special #4 female torx long socket to do it (Amazon). Thanks to everyone for chiming in, hope this helps someone else.

 

thanks for the follow up
often we never hear the out come

 

Ive had the same issue. Thos was a great help