1996 GMC Suburban heater blows on floor

Dear Aaron,
Your heater and air conditioner assemblies are partly vacuum actuated.
The parts underneath the dash are also largely plastic.
Many, if not most of the time, either there is a vacuum leak ( that you
probably cannot hear) or a plastic part that is sticking or has broken. Those parts like that are usually inside the housing & ductwork under the dashboard on the right side also under the glove box.
God bless your efforts.

most likely leak in one or more of the vacuum lines and or out door air damper not closing

If you need further help, I’m available over the phone at https://www.6ya.com/expert/mike_9693b5ad75773352

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

Could be the blower motor, or a restriction in the heater box, or a blend door problem.

The problem is probably the electric actuator on the air mix damper in the HVAC box - a common problem and probably needs replacing.

Could be a blockage in the lines to the rear unit.
Might be low on freon too. Or a blend door problem.
Can you check under the floor and see if one of the lines is cold ?

Sounds like hose got dislodged. Check under dash & fix. (If you can even get a hand in that area)

ur control panel with the 3 knobs is bad the board goes bad

common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.

Had the same problem. believe it or not i changed the gas cap and got heat all around. something about pressure.