Yes it is normal just no hot air - 2000 Chevrolet Suburban

1. When setting the temperature to MAX, blower level to FULL and outside air Vent CLOSED, no hot air comes out after 2-5 minutes?
If YES, when did you last flushed your radiator and is it full?
2. if more than 5 years ago, flush radiator system, instructions are usually in Owners manual. Use a bottle of Radiator cleaner, run egine hot for about 10-15 minutes, carefully open petcock in bottom of radiator to flush out radiator, WARNING, careful as flushed coolant would be boiling hot. As sson petcock is open and water start to flow out, carefully open radiator cap to enhance flushing flow. Use garden hose to fill radiator while flushing until water coming out from petcock is cold and clear.
Once clear, start engine, turn heter full and blower full blast and keep hose in radiator flowing full, leave petcock open until clear water flows out again. Once clear waters comes out, turn off engine,turn off garden hose and let water drain empty radiator. Once it stops flowing out, close petcock snug and put radiator cap on, pull off radiator coolant catch bottle, clean bottle for any debris and dirt. Drain any water, leave bottle empty and put it back onto its place.
3. Fill radiator with 1 gallon (4L) of concentrated coolant, top up radiator until full, fill catch bottle with concentrated coolant, start engine and keep it overflowing until no bubbles comes out and the radiator is fully hot. Once it is flowing good, close and connect everything. Drive with it and keep catch bottle filled as necessarry.
Good luck. Give as vote and good comment if this advise solve youor problem. Thank you.