98 4.0 heater not working

[98rngrfx4]

heater has worked forever now until about 3 weeks ago when it started getting cold. lol greatttt timing ford rangerrrr!

i decided to drain my radiator and put antifreeze in it. i pulled the drainplug and it didnt drain. looked like gunky hairy stuff. wtf? lol so i pulled off the lower hose and drained it got a water hose and and flushed it out until the crap came out. maybe this crap in there clogged up my thermostat and its stuck open?
truck never overheats.
wud this maybe cause the heat to not work?

wut other options shud i take if thats not it?

 

[chrwilkins30]

If your radiato was clogged I'd check the heater core or the hoses.

 

[98rngrfx4]

changed thermostat. still no heat..
how do i go about checking the heater core?

 

[shane96ranger]

Does your heater valve work properly? Also check to make sure the vacuum line isn't cracked and losing vacuum.

It will look like this black valve the arrow is pointing to.... yours will be very similar (I think this is a 4 cylinder in the photo).

 

[98rngrfx4]

i believe it is.. when the truck is off theres a little metal arm that is vacuum sunctioned shut. when i unplug the vacuum the arm opens up.
when i start truck and turn heat on, it opens up and theres no more vacuum in that line.

is that functioning properly?