No, I haven't solved the problem yet. I just can't understand why I can get nearly instant heat using the recirculate setting & not on any others. I just can't convince myself that it's a plugged heater core. Anyone else have ideas?

 

ever since you told me this i've been running my heat on MAX AIR, and getting good hot heat in the face. the only problem is that my feet are freezing.

this leads me to believe the fresh air setting just brings in far too much fresh air, which, at the moment, is colder than a witch's tit, and the heater core just can't warm it up. when my heat control is set on MAX AC, my heater feels nice and hot, exactly like it should. all my temperatures are as they should be, t-stat and temp gauge is dead on 180, hoses all feel exactly as they should.

i sure would like for someone to explain how the fresh air/recirc control works, cause i'd like to force mine to recirc for the rest of my life. if i want fresh air i'll roll down the damn window.

edit - also, with setting on max ac, i can get hot air within about 2 miles of driving, as soon as the temp gauge gets up to about 140, which doesn't take long. so t-stat and heater core are working fine, but there's too much cold, unheated air, getting into the air flow.

 

TTT, any other input on this issue?

 

Morning all. (I'll do the intro page after a bit ) I just purchased a 98 1500 5.9 and have/had a similar issue. Although I was never able to get heat with the setting at max A/C. Prior to my purchasing of the truck the water pump and T-stat was replaced, the radiator and the heater core flushed. Only get luke warm air no matter what the temp is out side or if I block of the air flow to the radiator.

I figured maybe the new t-stat was bad so I replaced it. I also re-flushed the heater core. Still only luke warm. Soon as I started driving the temp would drop. So, I'm searching every where trying to figure out the low/no heat issue. The other day I revved the engine above 2500 rpm's and noticed a blast of HOT air. I found one post about a vacuum check valve is bad if you can't get the air to come off defrost. Neglecting to read the whole thing I see "vacuum check valve" and "Heat".

Yesterday I removed both check valves. The nearest the manifold had a low pressure leak, not a big one, but enough to notice. After replacing it I am now getting heat in the truck. It's not as hot as it should, if I rev up the engine above 2500 the temp increases. Guess I've got a leak some where. As soon as I can find them, I'll be replacing all my vacuum line T connectors.

I'd say if you get your RPM's above 2500-3000 and the heat "comes on" start checking your vacuum lines. I've downloaded the manual provided here to see if there is any other check valve I am missing, though I don't think so.

Brian

 

Have you purged the air out of the cooling system? Revving the engine runs the water pump faster and shoves coolant through the heater core where (if the system is not bled) a lot air was. The fact that the system was opened twice leads me to think,"Air in system".

 

New thread, sorry for the hijacking.