1995 Suburban Heater switch problem

I have a 1995 Suburban that the Heater blower only works on Hi I have had the switches replaced and the blower motor in it and it still only work on high and when you switch to floor or vents it will blow out the top and bottom can only one help me with this problem thanks

The fan speed may be controlled by a resistor that is not part of the switches or fan. These are normally found on the casing of the blower motor with sensors that read the temp. The air door adjustment is usually vacuum activated, and either the hoses can cause problems, or the electrical connections to the door motors can get dirty. That's for most cars, but I don't know the circuitry for our suburbans in particular.

The fan speed may be controlled by a resistor that is not part of the switches or fan. These are normally found on the casing of the blower motor

Had the same issue with my Toyota Hilux. The resistor block consists of a series of resistors cooled by the airflow inside the casing/housing of the blower. When these are blown/burnt, you only have Hi because that selection gets full 12V without any resistor.

This resistor block should be somewhere near the blower.