1994 Wrangler No Heat in passenger compatment

My heater will not work in my 1994 Wrangler. I have replaced the thermostat and checked the coolant level but still have no heat when the heater is on. The blower motor works fine but only blows good air when the heater is on. Can anyone tell what the problem might be and how to repair it?
Thanks, Don

I assume that the engine warms up to normal temperature and that you mean "cool" or "cold" instead of "good air"

In my opinion, the only thing it can be is a clogged cabin heater rad. I had this problem on my Dodge Caravan and here is what I did.
1) Drain the coolant.
2) Disconnect the two hoses that go to the cabin rad
3) Connect temporary hoses (I use clear vinyl hose from Home Depot)
4) I used a small pump (the type of connect to an electric drill) to circulate at cleaning solution. (I was pumping from a bucket, into the rad and back into the bucket)
5) The cleaning solution was flowed in both direction.
6) They sell a cleaning product in the radiator section of automotive store. I used CLR.
7) I also let the CLR sit in the cabin rad for about 1/2 hour and then started the pump to go in both direction

A huge amount of crap came out of there. You could see the flakes of calcium. Make sure to flush very well. I also flushed with soda water. The soda water will neutralize the acid from the CLR.

After that, I got perfect heating.

On the van there was a switch that would shutdown the flow of coolant. It was vacuum controlled. I don't know if there is such a thing on the Jeep

Seb