Hello, I have searched for this problem but, I just can't seem to find it.
When I put it on defrost and heat, it blows out maybe luke warm. Barely getting any heat. But, if I put it on vent heat I am getting heat, it feels like it could and/or should be hotter but, it's definitely hotter then on defrost.
Any ideas as to what may be causing this problem?

Thanks in advance for any and all help.

By the way, I have a 98 Sport

 

In defrost, a/c is on (to dehumidify).

 

I understand that but, while idling I don't get out the heat that should be coming out. I did notice today that while driving or with the RPM's up, I do get heat. Starting to wonder if it's the water pump not getting things flowing properly at lower RPM's of if there is just air in the system. The temp gauge is staying at normal so, I don't think it's the thermostat. But, I could be wrong.
Any other ideas and/or suggestions?

Thanks for the help so far

 

ok so, i may not be brilliant but:

I don't think you have a problem, or at least, your jeep doesn't. As long as the defrost is on, the ac is on, and it will never get as hot as straight up vent with heat, because your ac is pulling moisture (which holds heat, sorta) out of the air. So whether you're driving and the engine is getting warmer, or idling, your defrost will never be as warm as your vent. . . . unless your ac is toast, and then you have a legitimate problem, like the one i faced yesterday.

i base this on three cherokees and the fundamental laws of thermal dynamics

 

thanks for the help, but, I just can't see how the defrost will melt the snow and ice during the winter time around here with it not blowing more then luke warm air if that.

 

Cold air MIXED with hot air makes warm air. When it's cold enough for snow/ice, the a/c compressor won't engage (most systems) in the defrost mode. Even if the compressor does stay engaged, the heater eventually becomes way more efficient at making heat than the a/c is at cooling.

 

This seems strange, esp since its warmer outside. My fiance's TJ has the same issue, and its only started to happen recently. The defrost was never this cold, so I am sure there is an actual issue.

On a side note, with cars that don't have a/c, what happens to the defrost then?