1999 cherokee heat question?

change your thermostat is not opening completely to let water flow thru engine

check the water control valve in the heater hose inline to the heater core

As soon as the vehicle reaches around 180/195 (depends on the temp of the t-stat) the thermostat should open and thereby filling the top hose with warm/hot water.
Are you sure the thermostat is facing the right direction? Is the cooling system full?
Here is what you can do: remove the t-stat, replace any lost coolant/water and run the vehicle with heater on full blast for about 15 minutes or until the temp gauge is showing about halfway. During this time be sure to monitor the coolant level in the reservoir.
If you still have no hot air you may have a blockage or perhaps the heater hoses are not even connected.

One or more of:

1. Your coolant level is low
2. Your thermostat doesn't close and needs to be replaced
3. The valve from the cooling system to the heater core is stuck
4. Your heater core is clogged

One or more of:

1. Your coolant level is low
2. Your thermostat doesn't close and needs to be replaced
3. The valve from the cooling system to the heater core is stuck
4. Your heater core is clogged

One or more of:

1. Your coolant is low
2. Your thermostat doesn't close and needs to be replaced
3. The valve from the cooling system to the heater core is stuck
4. Your heater core is clogged

The heat in your car comes from the heater core,it's a baby radiator under the dash,The coolant from the engine flows through it, So as the engine coolant gets hotter so does your heater core. If the coolant is not getting warm you might want to replace the thermostat,that will help alot.
Your blower fan gets it's different speeds from a devise called "the blower motor resister"
you will need to change that.

you have air in the system the best way i have found to bleed it is to remove one of the heater hoses at the engine and top off system

follow the upper radiator hose to the motor... it's in that housing.

what is the issue you are having before you spend lots of money replacing all the parts on your jeep ?

Robert

Oh and please take a moment to rate this solution.. thanks

I do not know a link to a diagram, but I can certainly tell you how to find the thermostat! Looking at the front of the engine, there is a large water hose at the top of the motor that goes to the left, and attaches to the radiator. Not the radiator end, but the other end attaches to the thermostat cover. It has 2 bolts to take out and the little thing between that, and the motor about 2" around that kind of looks like a spinning top, is the thermostat. It is easy to change. Make sure you get ALL the old gasket off and that both bolts go through the new one, and you should be in business!