Water pump?

I have a 98 with 4.0 that simply will not blow hot air from the vents.

I have flushed the core and found that water flows freely through the core so plugging should not be an issue. My jeep is an SE model and has a mechanical wire controlled blend door, so vacuum on the door should not be an issue. I have made sure that the blend door is free and operating normally.

I have checked everywhere for vac leaks and cannot find any. The system blows out of the vents at all RPM ranges and does not blow from the defroster vents unless defrost is on.

Sometimes it will blow decently warm for a time, then cold again. sometimes the air will get warmer as the RPMs go up while driving.

My jeep will heat up to only 203 and takes a while to get there. The thermostat was replaced with the higher end staunt unit and same with the cap. I have not had issues with overheating at all.

In addition the pump is not leaking and I have not observed any leaking coolant at all.

Is there a possibility that the pump has deteriorated to the point that coolant is not flowing through the system enough? Thats the last thing I can think of at this point. I am thinking it would be a good idea to change the pump anyway as the history of the pump is unknown. My coolant is nice and green and doesnt have any rust in it that I can see.

I need to get this licked as its starting to get a bit nippy out! :helpme:

If the pump wasn't working properly, you would be overheating. There is a valve under hood where the hoses go to the heater core. It is vacumn operated. Probably stuck closed.

98s dont have that valve.

AF runs through the core all the time 97+

When you say you flushed the core; I am guessing you either removed the hoses from the core and back flushed thru the brass connections or thru the inlet and outlet hoses.
Have you checked to see if the steel tube screwed into the water pump will flow water?
The steel tubes have been known to plug up with crud and rust....; remove the hose from the steel tube and check for obstructions.
The lack of water flow thru the tube would explain no hot air from the heater.
Four years ago while going thru the cooling system I noticed that the tube had little rust blisters on the outside and replaced it before it rusted thru.... You can purchase the part at a Jeep or Dodge dealer....