I need to replace my Hvac controls on my 2005 blazer 4x4 and I just want to know if there is anything I should know before doing this. It seems pretty straight forward but you never know about these things and I don't want to create more cost by screwing up. Is it just plug and play? I'm sure someone here has changed there's so please help. Thanks a lot

 

If you mean the dial/s in the dashboard just mark wires, maybe take pics so you can see the colors or the wires & where they go & make sure the replacement you got is the same as what it's replacing.
Are you sure it's not a vacuum leak in the hose leading to them? I know mine are sketchy at best & need to be replaced because when I have it on floor heat there is still some air blowing through the upper vents. That equals vacuum leak or bad actuator gate in the HVAC. More likely vacuum.

 

If it does crazy things like blow up, blow down hot cool hot cool always one or the other, check the vacuum line going to the tank in the driver's fender first they fall off and controls go nuts.

 

Why are you considering changing the HVAC controls? What is going on? Do you have manual or automatic HVAC controls? Manual has just red & blue around the temp dial; Automatic has numbers around the temp dial.