Heater not heating my Jeep

Air in the system ! Cooling fans not coming on ! You put the thermostat in right ? What engine ? 3.0 or 3.9 L ,Hook up a scanner that can view sensor data parameters , what is the PCM seeing from the cylinder head temp sensor .
I would think air pocket in the heater core because no heat coming . Heater hoses going into the fire wall , are both hot ? Hot water valve working ?
How to Fix Car with No Heat Easy

Not really, the heater core would still get hot enough to produce enough heat and usually the hoses will fall to the right spot making it hard to put them on the wrong ends. Why was the heater core changed? was it clogged? Did you flush the engine out to prevent the new core from clogging up? Have you looked into it being a stuck open thermostat?

probably have a blockage in the heater core or heater hoses to the core

Have you checked your water temperature sensor? A little thing like that can affect the heat put out with low readings coming out if it is not giving the right voltage. They are under $20 so that should help you out. The Jeep brand is originally AMC(American Motors Corporation) of wich the parts utilized came from different american brands (Alternator from Chevy or Ford, Motor from Dodge, etc.) But the put out for the heater core is the same. Just get the temp sensor changed and run the appropriate coolant for your Jeep year.

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

Air in the system or a clogged heater core. If it's air in the system, it needs to be burped. Click on my screenname, go down to Tips and Tricks, and follow the tip there on how to do so.

If the heater core is clogged, you'll need to blow it free. Follow the two heater core hoses from the firewall out to the engine. Disconnect them both, put one in a bucket, and use the blowgun attachment for an air compressor to blow into the other one. Then swap - put the one you blew into, in the bucket, and blow into the one that was in the bucket the first time. Reconnect the heater core hoses, and burp the system (again, follow the Tip instructions for that). Usually that will take care of it.

The only reason it won't blow hot air is because the water is not getting to the heater core. Check to see if you have a heater control valve in one of the two lines to the heater core. If so check to be sure that is is opening and closing. If it won't open then you get no water flow in to the heater core.

does the temp gauge go up to about half. If so heater core may be plugged.if temp gauge doe not go to about half i suspect a bad thermostat .

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow.

If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm.

If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air.

If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted.

One or a combination of these factors is likely the culprit in your case.

Flush the heater core 2-3 times, and if the obstruction does not clear, a new heater core is required.

However in your case, a cracked head is suspected - this will give out a plume of white smoke on startup - There is no smell, carpet dampness, or abundant moisture in the cabin? (this warns of a leaking heater core)

The coolant is leaking through a gasket or crack, and entering the combustion chamber. You dont see a leak on the ground because it is being burned up with the fuel.

Good Luck, and thanks for using FixYa - A FixYa rating is appreciated!!

unless you got visable signs of leakage its not heater core, but it could be pluged with sediment. take off both heater hoses and flush it both ways until it runs clear. you can also mix a little baking soda and water and pour in core and let set for a while and then flush.