Dash vent cooler and floor hot

[Monk]

We'll ever since I've owned my rig. Temperature Seem to fluctuate with front heater hvac

I'll start truck drive and around 20mins or so later ,the floor/vent temp goes down for 10mins or so then back to hot.

I've put in (just because eventually I'm sure would go) new tstat, heater control valve,

Heater core was changed in summer so flush all system out then.

My defrost vent is Always Hot/warm, floor vent goes room temp then hot , varies most at floor

Seems like when my cab is warm heat goes less hot outta vent,

If I put in a/c mode (compressors unplugged for winter) feels warmer but still temp shifts hot/warm/cooling/


Would this be my blend door actuator? Lol I'm stumped but this is now my obsession , I also tryed a new heater control ,and didn't help/change,

The back heat running gets hot!!!

It just I believe front should stay hot if I leave at hottest level.


Any ideas,what I would check next? So all my vents always warm .

Also front dash vent, goes hot then warm then hot as well


It's a 96 h1 with the upgrad system

[Kapman]

When the floor vent changes temperature does the volume of air coming out of the vent change? I could see if you had a vacuum leak on one of the actuators it could spontaneously redirect air flow leaving your feet in the cold. I have my upgraded hvac completely exposed right now for some other work so if you want some pictures of what your system looks like just let me know.

[dwaxman1]

I just upgraded my HVAC kit in my truck and needed to Change the Vacuum Pump to get the proper air flow...and mine is a 96 also...

[Monk]

Mine is the upgraded syst.

Ya it stumps me, when in the heat setting say windshield/floor the top is warmer (not hot) floor is Luke warm/cool , but after a 30mins can change to colder Orr can go warm for a while.(10-15 mins)No change in blower speed air pressure.

In normal setting say on face vent,it will be Luke warm/cool,

Then I switch to "max AC" the face vent get super nice hot, it seems when the out side air closes works super.

Soooooo I put a tee fitting and tried to keep vacuum on steady on fresh air door(so was closed to fresh air) and all seemed warmer all settings.

But. .........I forgot after a 30min ride windows want to fog up so I put back to normal vacuum ,

I was wondering would a blend door itself make warm then cool or just have cool steady? The actuator moves defiantly .

Back heater is nice and hot, but I drive with my dog all the time so don't use that back heater much.

My motor temp is normal at 180-190 .

[Monk]

We'll good news, problem solved!!!!

Took of blend door actuator yesterday and moved air door flap and had normal spring tension

And I could turn and hear slam ,that was fine.

So , lol almost gave up ,as thought I was defeated .

Soooooo I left the air door closed (heated air) /actuator removed ,went for a spin ,and heating was perfect.

Seems after a while of driving the blend door actuator

Would open/close (on its own) and make everything go cold then after while warm, intermittent .

Started truck this am tried a long drive again ( to make sure I wasn't dreaming ,hehe)

And drove a good hour , and heat worked on all settings .

Not saying its a furnace, but for our hvac I'm happy totally,

I put on actuator and issue happened again, so I took actuator off again, till I replace, now heat is great.

On a good note at least I shouldn't have to worry about cooling this year as replaced so much hehe