Hot air through floor in 99 Suburban when blower is switched off

Vent doors not open correct

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

MODE SELECTION IS VACUUM OPERATED. DEFROST AND FLOOR ARE A DEFAULT MODE WHEN SYSTEM FAILS. YOU HAVE A VACUUM LEAK, FAULTY VACUUM SWITCH ON DASH CONTROL UNIT OR A BAD VACUUM MOTOR IN DASH

If you don't hear a thud or noise of a flap opening or closing when switching between hot and cold then a lever is probably broken.

Hi - There may be 2 separate problems. On my 1991 Lincoln Town Car, there is a Thermal Blower Lockout sensor that disables the heater from blowing until the engine temperature reaches a specific temperature. This way if you have vent or floor settings and 90 degrees set and it is winter, you won't get blasted with cold air. When the vehicle warms up, the TBL circuit enables the climate control to blow the hot air. If you use the flr/def instead of the floor or vent control, the TBL should not prevent the heater from working even with a cold engine. On my car, the TBL went bad and always prevented hot air from blowing on the floor and vent settings, even when the engine was hot. Another thing to check is a thermal limitor resistor. It is designed to cut off the blower at very hot temperatures, except if the blower fan is in the hi setting.

As far as the A/C is concerned, can you verify if the clutch is engaging or not? A rapid cycling of the clutch is an indication of low freon. If you are absolutely sure that you are fully charged on freon, I think there are 2 possible causes: (1) Bad pressure switch on the accumulator is indicating low freon that is telling the compressor not to work; (2) a blocked orifice tube.

this is because you have a bad switch which has gone bad and you need to replace it or either try to bypass it through another circuit.

Either Your fan switch is burned out or you blower motor is no good, your blower motor is on the passenger side under the dash. Before you replace any parts you need to check your fuses and relays under your hood and in the car. Usually if your fan switch goes bad you will still get some air blowing thru the vents, so my guess would be blower motor, If its not a blown fuse or relay.

Hope I was avle to help, glad you up and going.

yes those controls are vacuum controlle. Could be as simple as a bad hose or connection.

I would suggest replacing the blower motor resistor. When this component fails the blower will only work on one spped or none. This is a very common issue with all automotive models