I HOPE someone might help ,
We'll my 96 N/A diesel has the upgraded system hvac,
I have a bunch a weird issues, first the issues,
I start truck and back heater is warm in few blocks, front is cool,
Then eventually front starts to get warm, then after 20-40 mins of driving starts to cool, (front), then after 10-15 mins goes back to like warm. Changes temp ever time I drive like that .
My A/c compressor I unplugged for winter,
Ok when setting at defrost and floor ,floor blows cool all the time
If setting to just floor is can vary sometime warm other cool
I normally keep my settings to face vent/floor then floor always warm/hot
And face vent varies, will stay warm lots but then (seems like once cabs warm )face vent blows cools and only floor blows hot,
Defrost only will mostly be warm/hot but some times stays cool ?

Things I've done so far,
Flushed rad (was dirty)
Made sure coolant was filled
Purge system a lot , bleed few air bubble
Put in a napa T-stat (ran bit cooler form 200 to now 180-190)
Put a new water control valve last month
Bleed air more
I had a new heater core put in at summer time,
I sat in passenger seat and turned temp **** hot to cold
And then air flow actuator moved, every time I move temp actuator moves,
But never goes hot, just arm

Oh also if air temp is cool, sometime I put setting to max ac, and blower goes hot, this thing stumped me

The back heater is HOT!!
But my front is in need of advise?

 

My 2001 is new to me but appears to do the exact same things. I was noticing tonight just how hot the back blows! It's pretty hot compared to the front.