Explorers are always fun. It takes a trade technician about 6-7 hours. First you disconnect the battery, drop the steering column, remove the center console, remove the dash. Then you can see the case, but you still can't get to it. Then you have to recover the refrigerant from your A/C system and remove the case. Now you can separate the case and remove the heater core. Sounds like fun doen't it? Good luck. Let me know if you have any more questions. I'll be happy to guide you through it. I've done it quite a few times myself. My first one took about 9 hours.