I just rebuilt my standard heater it has a small fan and motor under the circular housing within the heater core. I found that since my truck had been sitting a while the bottom tube where it entered the core had a weeper. It is really easy to restore, remove it by removing the nuts on the studs and disconnecting the one wire to the switch. Look for evidence of leaks and fix, I cleaned and repainted all the housing and it looks good. If you want to covert to 12-volt motors are available for that too!