heater problem

[chrisl757]

It's cold here (5 degrees with windchill), and my heater is not working.

96 xj, 160K, 4wd, 4.0L

I get cold air blowing on the floor in the HEAT mode. While in DEFROST, I get hot air blowing onto window, and in VENT, I get lukewarm air blowing through dash panels.

I have checked the vacuum canister and lines which look ok--at least I couldn't see any breaks or deterioration. The fan blows properly at all speeds and in the right configuration (Heat blows to floor, vent blows to dash, defrost blows to windows.) I have flushed the heater core, and it is clear.

If the defrost blows hot, I am guessing my coolant flow the the heater control valve is ok. the heater control valve is still in place: one hose line is hot, the other hoseline is warm. Could there be an issue with the heater control valve where it works sometimes but not others?

I watched the blend door cable move through the range of cold to hot and can hear it changing position. But I cannot see the blend door since it's enclosed.

If this sounds like a blend door issue, then how do I pull the ducting apart easily to check to see if the door is broken?

I don't know if this is a related problem, but sometimes I get a strange noise (Sounds like metal rubbing against a moving part) from behind/under the glove box when the fan is on the high setting in the HEAT mode. If I turn the fan speed down the noise goes away. but the fan still blows without difficulty.

Please help. It's cold out.

[chrisl757]

I am not sure if I have a vacuum leak or not. the system "looks" ok, but I'm wondering if there is a way to test it to see.

If my vacuum is not working properly, I guess that would explain how the doors are not operating for heat and vent when the temp control is set to high.

Is there some sort of vacuum gauge that you can hook up parts of the system to?

How do you do that reliably to see where/if there's a problem?