My Jeep's (GC) heater won't get hot!

I know, I know! Why would you need it now (summer time, 100+ heat outside). But winter will be on it's way sometime.
I put it on defrost (fan on), temp switch on "heat", A/C switch off (engine heated up good, 200 ). Just cool air coming out the vents (vent doors are working correctly). If I turn off the fan for a bit, then turn it back on, I get a small burst of heat. Then it goes right back to blowing cold. My heater core is not leaking (no wet floor, no smell of coolant). I'm thinking the core is plugged up a little (not letting the coolant flow through enough).
I did find this on you tube.
http://www.youtube.com/watch?v=dcL_0TWeZJY
Seemed to make sense to me, I'll give it a try. Just wondering if anyone out there has been down this road, tried this, and if I'm on the right "diagnostic" track or have suggestions before I do this?
Thanks

run the engine, until warm. turn on the heater. check the valve to be sure it opens. feel the hoses, both in and out of the firewall. a clogged heater core will be cold, but so will a core with a valve that doesn't open. you can get a garden hose repair kit, and use the male barbed fitting to plug into the heater hose. disconnect the other end, and turn on the water, and see if it flows. swap the fitting onto the other side, and do it again. you'll see if crap comes out, if it's getting clogged, or nothing will come out, if it's plugged.


this is the fitting, i used.

The trucks plug up heater cores for sure....I'm betting it's plugged good. A little flush agent in the cooling system would maybe loosen up some of the crud if you drive it for a hundred miles or so....
Maybe try the "reverse-flow-garden-hose-trick".

I back flushed my heater core through the lines in the engine compartment. Did this a bunch of times, back and forth, till the water ran clean, and steady both ways. Then I flushed the entire cooling system till it ran clean. Emptied the entire cooling system. Filled it up with new coolant, and water (as per the Chrysler specs). Started the engine, ran it up to temp. (thermostat opened, coolant dropped), added more coolant/water (in the over flow bottle too), put the cap back on (I'll check it again when she cools down). Car running, heater/defroster, and fan motor on. Lots of heat coming through now. Heater core lines are both hot, and hot. I think I've licked this one.
Thanks again everyone!