Heater problem on Isuzu Trooper?

First of all check both heater hoses.
If both of the heater hoses get hot at the fire wall then the blend door in the heater housing is either broken or is stuck and you would need to remove the dash and pull the heater housing out to fix the blend door.

If the hoses are geting hot the actuator is most likely what you hear and when the door brakes loose from it you wont get any warm air.

This will help.

Thanks.

I recommend you to check this related solutions for better understanding of problem:-----

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