Ok I bought a V8 1999 Jeep Grand Cherokee Ltd. With climate control this fall.
Heat was lousy but had some.
Every thing I read said it was the blend door so I bought one. Took down the glove box etc. Guess what? It looked like it had already been done.
I went ahead and took off the motor and pealed off the tape to check if it was working, it was.
Now I get zero heat. I have the blend door compartment open and the blend door held half way open. Core cold!
I pulled hoses and flushed out core. Still cold.
I read there is no heat valve in this system, nor did I notice any, seems a straight shot.
I also believe the heat controls (which I have on "Hi" ) only regulate the blend doors.
Can anyone tell me/suggest what the heck is going on? Please! It's cold here.
Thanks

 

If the core doesn't get hot and you know the lines are clear for flow, I can imagine 3 things:

-There is air in the heater core circuit and it's causing an air lock, i.e., a bubble that it can't push out on through the circuit.

-That system has a valve to prevent hot coolant from circulating through the core when you don't want it, i.e., summer, and that valve is closing when it should be opening.

-The water pump impeller is rusted/eroded away to the point that it can't move coolant through the core.

 

Welcome to CF!

Obviously you have no coolant flow thru the heater core. Do the heater hoses get hot? Here are a few things that can cause this;
Plugged core. You just checked this.
Internally collapsed heater hose
No thermostat
Bad water pump
Air blockage in heater core. Make sure the hose from the thermostat goes into the lower pipe on the core. This will naturally bleed out the air by gravity.

As you stated and I do believe there is no coolant control valve in the heater system. There is a messy way to check for flow. Take the heater hose off the water pump and cap the pump fitting. Direct the heater hose over the fender and crank or start the engine. You should have coolant everywhere!

Good luck! Oh, I see Red River got to you while I was typing.

 

I have a 2000 XJ with an inline 6, auto, 4x4.
When I got it I had to take it back because it did not heat well.
The guy I got it from claims he flushed the system out and did something to 'vacuum lines-vacuum block-vacuum????' sounds like a load of stuff but I need to know tomorrow when I go out and flush out the heating core that there is a second route I can take to correct not getting heat.
The lines are hot, real hot to the touch so I'm thinking it's getting hot water.
I believe the upper line is the return line and that is the one that is hot. I didn't check the lower one thinking it was the supply line and ought to be hot if the return line is hot, but I'm no mechanic, just an old man wanting heat in his Jeep.
Is there something under or behind the dash, accessible via the glove box or other means that can be seen and replaced or adjusted or ????? to remedy this problem.
Thanks you guys have a lot of experience, share some with me?
Doc

 

First of all, your jeep doesn't use vacuum to control the heater. It's all done with electric stepper motors. Behind the glove box, there is a motor that controls the blend door, regulating the temp of air flow. It's all plastic and the shaft that connects to the blend door sometime shears off. It's also possible the motor is not getting power or is burned out. As I said, this is a stepper motor that moves a little with every power pulse it gets. With climate control, there are 2 doors, one for each side. In order to get to the one for the passenger's side, you have to remove the whole dash.

Check out wjjeeps.com for lots of info about your jeep. It will explain how to take your heater apart. There should also be electrical checks you can make.