Cadillac Repair: heater hoses into heater core, heater hoses, air plenum

Question
No heat in a 94 sedan deville 4.9L. Only 53000 miles.  Replaced the Thermostat, exposed the heater core and when started, found it did get hot, not super hot.  Also found the air plenum control rod had no nut of any kind on the threaded end.  Is there supposed to be one?  The motor that moves the arm works just fine.  All the heater hoses look new.  When I followed the heater hoses from the T to the heater core, the hose attached to the T was attached to the bottom pipe of the heater core.  Is this correct?  I'm trying to do this in 15 degree weather.  Should I flush/replace the heater core now that I've gone to the hassle of getting it exposed? Any help would be appreciated.

Answer
There is NOT supposed to be a nut on the threaded rod.

1. Put the system on FULL HEAT, Watch the threaded rod for 3 minutes as it should come towards you. After the 3 minutes, Unsnap the threaded rod from the plastic snap holder and see if you can pull the threaded rod any further towards you. If NOT, Snap it back in the plastic connector while holding the threaded rod as far as it will come towards you.

See if you have heat. If NOT, Replace the heater core.