The exact location of the Chevy Astro Van fuel injection pump fuse is dependent upon the year of the vehicle. The fuel injection pump fuse will be in the fuse box. The location of the fuse will be listed on the inside cover of the fuse box.
The fusible link for the headlights on an Astro van is located in the fuse box under the dash just to the right of the steering wheel. There is also a fuse location on top of the battery in the engine compartment.
I have a 1996 Astro van and I'm having trouble too. My fan motor sticks. It has for a while. Its not the heater but the fan that has draged. I can get out and pound on the casing, and sometimes it starts up.
Drain the water from your 1998 Chevy Astro cooling system. Remove the water supply hoses from the heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
High speed uses a separate fuse. It's in the fuse box under the hood, large green 30 amp. If the fuse is not blown, suspect the blower resistor assembly at the front of the ac/heater box, just behind the washer bottle. Occassionally the fan switch itself may be defective.