Welcome and I'll move this over to the Cherokee area..


But sounds to me like a vacuum leak, some of teh other XJ guys will know for sure..

 

things to check would be coolant level, if you have a lot of air in your system you will have little heat. Top off and bleed the system. Check out your water pump too.

 

There is a diverter box just to the right of center under the dash. It has a vacuum line that goes to it to open and closes the door to the heat duct. It fails in the defroster mode. Check that the vacuum hose has not become dislodged. If that is OK the next thing to check is the plastic heater valve under the hood on the distributor side of the engine. They often freeze up and when called upon during the winter months are frozen in the closed position and allow little or no circulation of coolant into the heater core.
HTH

 

my jeep has no heat either. i bought the thermostat so i'm going to be changing it tomorrow.

 

Check your temp control cable.
Its the COLD>>>>>>>>>>>HOT slider.
Most times some minor resistence can be felt.
The cable is connected to the HVAC unit under the dash with a small clip.
These clips can either fail or allow the cable to become detattched.
Right under the dash on the passenger's side.

Look up and move selector. You should see either a cable moving a lever OR a cable sitting there in mid-air.

Sometimes the cable mount pops out also



You don't have to contort yourself to see this. Just place the back of your head on the front edge of the seat bottom. TIP: Having a flashlight helps

 

do you have a heater valve in the heater hose? Some models have this valve some dont. It's located inline with one of the heater hoses. If it fails the hot water cannot flow to the heater core.
Do you have a sliding temp control or a roatary dial ?? The sliding type usesa a cable to change temps the dial has a servo that opans/closes the air door...??