Do I need heater treater?

So my 99 XJ is having some heater issues. The heater only blows luke warm air. Did some searching on the board and I'm thinking my blend door is bad but wanted to run it by you all before i drop the money on a heater treater. So the air conditioner works perfect. All the heater controls work (put it on defrost and air blows out defrost, put it on floor and air blows out floor....its just not hot air). I flushed my heater core, not much really came out and both heater core lines are warm. Sometimes when i first switch the temp to heat the initial air out of the vent will be hot for three seconds and then it turns luke warm. Winter is coming, i need heat....does this sound like a blend door issue??? Thanks!

So I had this issue last time I was up in OR/WA, just couldn't get enough heat to keep myself warm... While I was up staying with a friend I had some issues, so also took care of some deferred maintenance... I put new heater hoses on, I pulled the metal hose doodads out and cleaned them with a bore brush (they were full of years of heater mud), and then I back flushed, and flushed the heater core several times, then hit it with compressed air (to blow the water out to be replaced by coolant). My heater is now so hot I could probably make popcorn with it.

This is an easy place to start, about $20 in hoses and fittings, and it's really something you should do anyways.

Just an FYI, I've got a 1990 with a closed cooling system, so the heater lines are an integral part of my cooling system whether I like it or not.

I already inspected and flushed heater core. Somebody on here has to know if these are the signs of a failing blend door or not?

Did you inspect/flush lines to the heater?

IIRC the blend door should be directly accessible from the passenger cabin, underneath the passenger side, look up, and there's your blend door. In that model year I think it's electrically controlled, so you may need to turn the car on, and move the controls around a bit and see if it moves.

Also, there is a thermostat switch down around there somewhere which tells the controller when to open/close the blend door.

Yes i flushed the core through those lines, they were clean. Guess I'll crawl under the dash and have a friend play with the heater controls and see if i can notice anything not working properly.

For a cheap fix in the winter months, a quick bypass of the heater control valve is quick and dirty. Get about 9 feet of black heater hose, and connect it direct. This is what i did on the 1995, and it worked great because my heater control valve was sticky and leaky. This will not fix a blend door issue, but it will rule out a flakey heater control valve.. Best of luck in your search for warmth!!!

97+ doesn't have a heater control valve.

It could be the blend door, the blend door motor, the plastic shaft, or the selector knob. They are really easy to get to on the later model years. If you look up under the passenger side dash it is on the left hand side almost right above the trans tunnel. You can see it move when you turn the adjustment knob. Three 13mm screws hold it on. The one in the back is a little bit of a PIA to get to.

So my blend door is not the problem. Blend door opens and closes fully, blend door motor works fine, everything works. A co worker told me to check my thermostat?

Tom, you can check if your thermostat's working by looking at your temp gauge,(if it's working). If it never goes above 150*-ish, then it's probably stuck open. You didn't say it was overheating, so it's probably not stuck closed. After it has run for several minutes, check the upper hose, it should get hot once the thermostat opens. This is a lot easier and less messy than taking it apart to inspect it.

Well i doubt its the thermostat then, it stays at a constant 210 degrees. What else would cause heater to fail?

After doing some reading i have found others say the electric radiator fan is supposed to come on with the a/c and defroster. My electric fan cycles on and off as soon as any type of heat is turned on, not just defroster. Is this normal? Could this have anything to do with my heater issue?