I have a 1998 Chevy 2500 4X4 and cant get good air flow through vents blowe is on hiogh but hardly any air moving

Check heater tap is operating remove heater hoses and back flush the heater core to check flow, check thermostat.

usually evaporator is block I mean the outside. debris cause no air to flow or little.

sounds like you have a bad blend door motor that is stuck in the middle allowing for all vents to blow air... locate the motor under the dash and remove it. manually move the lever and see if it changes the flow.. check for power at that motor to make sure your getting the signal from the dash then you'll have found your problem....

Hello and welcome to FIxYa!
You may want to check on the vents for it can be closed half way. If the vents are good then the problem will surely be on the blower itself. It can be worn out that's why the blower motor blows weak. Once replaced I believe you'll be good.
Hope this helps and thank you for using FixYa! Have a good one!

The most common cause is a bad blend door actuator which controls air flow throughout the cabin. When air flow only flows from 1 section (either floor, vent, or defrost) it's an indication that the blend door actuator is either stuck or broken.

Your vehicle uses electronically controlled blend doors to direct th air flow from defrost to vent and to the floor . If the door motor is bad then it will stay at a fixed position so you will not get the air to flow out the defrost ducts. There are at least two of these one for air blend and one for fresh air. They are located on the passenger side usually under the plastic cover and have a wire harness that plug in and are usually shaped like a piece of pie.

change your cabin air filter, it is probably clogged not allowing air flow. see your owner's manual for instructions. I hope this helps

replace the cabin air filters

YOU HAVE ADD THE WRONG FREON ALL CARS MADE AFTER 1996 USES R/134. FLUSH THE SYSTEM, ALSO CHECK THE BLOWER FAN FOR DEBRIS

You probably have a vacuum leak on the passenger side. its a small plastic hose some times they come unpluged from the engine. or brake.