1999 Cherokee Classic 4.0L Heater blowing cold

new to me 1999 Cherokee Classic is blowing cold on a non-A/C outlet setting and the air temperature selector to FULL heat.

A couple of interesting, but possibly not relevant facts:

o the heater hoses (2) do not get hot like the large diameter engine to radiator hose with the engind a operating temperature

o recently purchased the jeep so I have no repair history

o both the heater hose (engine to core) and return hose (core to engine) appear to be new with screw-type hose clamps. Also the gasket on the thermostat appears to be a amateurish job. (I am speculating that some one tried to fix the no-heat problem by replacing the thermostat and hoses)

o dealership told me that the 99 has no heater control valve and that the flow of water to the core is constant with heat being controlled by the heater door mechanisim.

I am leaning to a core replacement but would like to test to see if it is blocked.

Questions:

1. Would water from a garden hose pass directly though the core if both ends of the hoses are diconnected.?
2. Is there another way to test the core flow?
3. How would you test a heater doors to see if they are working?
4. Any other ideas?

The heater core is just a smallish radiator, and water should flow through it pretty easily. Both hoses should be hot. The upper heater hose should be as hot as the upper radiator hose when the Jeep is fully up to temp. Not a terribly uncommon problem. See this post:

http://www.naxja.org/forum/showpost.php?p=245152782&postcount=4

Might just need to backflush it, but I'd recommend going through the cooling system if you don't know when it was last serviced. A well maintained cooling system will save you a lot of headaches (and also guarantee you have heat).

Thanks for the post. Perhaps you would know, I looked for a "flushing/cleaning solution" at the parts store and found only solutions for plugging leaks. I have no leaks so I elected not to use something that might further plug the core.

What is a good cleaning solution? I have some TSP (tri-sodium phosphate) and I have CLR, would either of these work? My plan is to disconnect the heater core hose and the core return hose and flush only this portion of the cooling system. Then go to Grease monkey and have them flush and service the entire system.

I think I used a Prestone flush; it was definitely a cleaner, not a stop-leak product. If the coolant looks good (or you're going to have it serviced soon), I'd just backflush the core and see what happens.

I've read about people using CLR and such, but I was concerned that too aggressive a cleaner might create more problems, so I just looked for something intended for cooling systems. Any parts store should have something like that on the shelf.

Thanks for all of your help. I backflushed the core by disconnecting the heater hose and return hose, did a cooling system flush and service. Bingo, heat!

Thanks again.

If you go on YouTube, Eric the car guy has a video on unclogging a heater core.
He uses CLR and air compressor, he does this on a 4.0 Jeep also.

I've just done mine using only a garden hose and Vanish Toilet Bowl cleaner.

Followed Eric's direction except I used garden hose and Vanish.

I had to do it twice to get it cleaned out.

I let it soak 30 minutes each time and now I got major heat.