Interior heat problem?!

[95OBSMan]

95 RCSB GMC, 5.7 TBI. Unmolested/ all OEM components under hood.

So after reading at least 19 pages relating to what I think is my problem, very good info on these pages, my problem is very weak heat coming from dash vent as well as the floor in any combo by the dash HVAC control knobs. No A/C on and dail turned all the way to the red.
1- Brand new radiator, new hoses, thermostat, flushed engine block throughly, reassembled with no leaks, none from heater core either.
2- using IR hand held temp. tool upper and lower rad hoses temps read as they should, can see by this method that thermostat is opening/closing. engine does not run hot according to gauge on dash, nor does it "smell" like its running hot. daily driver
3- Blower motor works great, produces good air flow through vents, dash/floor.
4- So from my understanding from my symptoms is 1- back flush heater core with gentle pressure, this is going to differently count as the stupid question, which way is which?! 2- after doing this my problem still exist, blending door? if so where is that located at? 3- If I remove blower motor and find that the space between the fins and cores are filled with crap, would this cause no heat transfer inside the heater core housing?! kinda stupid, but had to say it, I've learned anythings possible, if back flushing heater core doesn't solve problem, then new heater core, new HVAC control panel? Any info or insight on my problem would be greatly appreciated!

 

[Schurkey]

Perhaps a moderator will move this thread out of "Engines" and into "OEM and Custom Interiors".

95 RCSB GMC, 5.7 TBI. Unmolested/ all OEM components under hood.

very weak heat coming from dash vent as well as the floor in any combo by the dash HVAC control knobs. No A/C on and dail turned all the way to the red...

2- using IR hand held temp. tool upper and lower rad hoses temps read as they should, can see by this method that thermostat is opening/closing. engine does not run hot according to gauge on dash, nor does it "smell" like its running hot.

You've proven that the thermostat is not at fault--opening too early/too cool/stuck open.

IF this was the thermostat, I'd expect the engine to run too cool, not too hot.

Use the same methodology on the heater hoses. Supply hose should be as hot as the upper rad hose, return hose will still be almost as hot as the supply hose--perhaps ten or twenty degrees cooler depending on ambient temp.

3- Blower motor works great, produces good air flow through vents, dash/floor.

You've proven that the A/C evaporator and heater core are not plugged with debris--leaves, pine needles, mouse nests, etc.

4- So from my understanding from my symptoms is 1- back flush heater core with gentle pressure, this is going to differently count as the stupid question, which way is which?!

Hose from rear of intake manifold is the supply to the heater core, hose going to water pump or radiator is the outlet from the heater core.

To reverse-flush, you'd pump water into the hose going to the water pump or radiator. Disconnect the hose at the rear of the intake manifold so you don't push the debris into the engine.

2- after doing this my problem still exist, blending door? if so where is that located at?

Heat/cool blend door, or it's actuator, or the actuator wiring. I'm told that actuators are a common problem (the internal gears are plastic, and the teeth strip off of them) although I've not had trouble with mine. (Mine are noisy when they move, though. So perhaps "trouble" is on the way.)

I suggest turning the ignition on but not starting the engine. Adjust the temperature from "hot" to "cold" and back. Listen for the actuator. If you don't hear it, or if it's making odd noises, chances are it's failed or has bad wiring. If it sounds reasonable (compare to the sound of the other actuators--floor/vent/defrost, and on some vehicles there's a manually-controlled "air intake" (recirculation) actuator and door.)

If the actuator sounds like it's working, you could still have a problem with the air-door itself. That's a "dash removal" and "heater-box removal" major project.

3- If I remove blower motor and find that the space between the fins and cores are filled with crap, would this cause no heat transfer inside the heater core housing?!

You'd be more likely to complain about poor air flow along with poor heat. If you have good airflow--and you say you do--this isn't a problem.

kinda stupid, but had to say it, I've learned anythings possible, if back flushing heater core doesn't solve problem, then new heater core, new HVAC control panel? Any info or insight on my problem would be greatly appreciated!

If the control panel causes the actuators to move...it's not the control panel.






My '88 K1500 got the better of me a decade or so ago. I "thought" I had poor heat. Replaced the heater core, no improvement. 205 degree thermostat, no improvement.

Turns out that the heater was working just fine. The problem was that there was an enormous cold-air leak into the passenger compartment due to rotted foam seals between the steel of the cowl area, and the plastic of the heater box inlet to the HVAC blower fan.

Rotted foam seal was above the HVAC blower, where it meets the steel cowl.

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[someotherguy]

In OP's case I believe checking temp of both heater hoses would be my very next step.

If you note the return hose is considerably cooler, then yes, backflushing the heater core out is recommended. Just beware that moving the supply hose around risks breaking the quick connect fitting on the intake, if it's original.

Richard

 

[95OBSMan]

Schurkey, thank you for the insight and info, a lot of trouble shooting today thanks to your time and experience, this is todays task is to get this sorted out, someotherguy, thanks for the heads up on the quick connect at the intake manifold, I saw one of those at the parts store in the help section the other day, only one hanging there, better go buy that now b4 getting into this project, I did not check the temp on both of the heater hoses, that step will tell me a lot, can't believe I didn't check that out, just assumed that "hey" both upper/lower rad hoses have temp heater core does as well, not the case here, and yes, everything I will touch today concerning this is original 114k and one owner, when I did the tune up, everything I removed was original, if that doesn't show you they built parts to last, I don't know what does!! I hope its a back flush and or an actuator, trying to stay positive, but with my luck, "dash removal" maybe needed, thanks again, well out to the garage and time to test with the info I now have, I will post back with what I find out, one way or the other this will let me know "what's working and what's NOT working"!

 

[95OBSMan]

Ok truck has been sitting inside garage, cold, turn ignition switch to just on position, not starting motor, 1st turn fan motor "blower" switch to highest setting, moves air really good through floor vent, move switch to all settings on dash control, confirmed visually and by sound all 3 actuators working,(thats all I can see/hear or have found) 2 of them hardly make any noise durning there movement of operation, moving from drivers side to passenger side is as follows, 1st actuator is on the bottom of "box" where the floor outlet is, this one functions well hardly any noise, this one moves air flow from floor to dash vents to defrost or combo of defrost/dash vents, 2nd actuator is located almost behind the ashtray, this only moves when the temp switch is moved for hot/cold, it moves but with some gear noise, I'm sure I'll have to replace this one, 3rd actuator is located behind blower motor and almost against the firewall at the bottom of the black plastic box, this one only moves when I press the recirculation button, it moves with hardly any noise and moves the "big flapper" bad description, easily with no trouble either way, it seems to seal very well, so when I turn the fan switch to OFF, ignition switch still in same position "on" there is a noise coming from either the blower motor or that actuator?! Is that normal, did the factory set a default for blower motor to barely run even though the fan switch is in the off position? Just updating and doing what schurkey has pointed out for trouble shooting, without getting thing hot yet. Next is to drive it and get thing up to operating temps. I'll post some pics

 

[Rock Hard Concrete]

Every time I have had poor or no heat output it has been that the heater core needed to be back flushed. You might have to do it a couple of times to get everything. So, back flush, reassemble, drive until the heat gets weak (this might take a few months of driving), then once you flush it again it should be good for a long time.

 

[east302]

2nd actuator is located almost behind the ashtray, this only moves when the temp switch is moved for hot/cold, it moves but with some gear noise, I'm sure I'll have to replace this one,

That is the actuator for the heater core. If it isn’t opening or closing completely, air isn’t going to flow over the core and you won’t have full heat.

The ratcheting or crackling sound typically means that the internal gears are cracked and not long for the world.

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There is a notched silver position indicator dial on the actuator. Watch it turn as the temperature dial is turned.

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It should rotate smoothly from (roughly) the 11 to 1 o’clock position. If it hesitates or doesn’t go all the way to the lines marked on the housing, it’s probably going to need to be replaced.

That assumes that the coolant flow checks out and isn’t also an issue.

 

[Schurkey]

all 3 actuators working,

Excellent. Control head seems fine. Actuators may or may not be OK.

2nd actuator is located almost behind the ashtray, this only moves when the temp switch is moved for hot/cold, it moves but with some gear noise, I'm sure I'll have to replace this one,

Mine is crazy loud. But it still works, the air gets cold or hot depending on the control head button.

3rd actuator is located behind blower motor and almost against the firewall at the bottom of the black plastic box, this one only moves when I press the recirculation button, it moves with hardly any noise and moves the "big flapper" bad description, easily with no trouble either way, it seems to seal very well, so when I turn the fan switch to OFF, ignition switch still in same position "on" there is a noise coming from either the blower motor or that actuator?! Is that normal, did the factory set a default for blower motor to barely run even though the fan switch is in the off position?

The actuator closes when the HVAC isn't used. Mine closes whenever I shut off the ignition. Keeps outside air from blowing into the passenger compartment when the vehicle isn't being run.

 

[95OBSMan]

Drove truck yesterday from "normal" driving in town stop and go, to getting on the highway and running the hell out of it, drove it like I stole it, outside air temp here was 75 degrees, get in the driveway, pop the hood, get the IR hand held temp gun out and upper and lower rad hoses read "normal" engine still running, heater hoses, inlet side hot, outlet not so great, so as you guys have stated back flush heater core, and while I'm at it I'll replace the actuator that east302 pointed out. So as RHC pointed out multiple "flushes" maybe needed to clear out the heater core, this also got me thinking, bought the truck this summer(June) was hotter than the hubs of hell here, no need to use the heater, with the heat from this summer found the weak spot in the 114k all original engine cooling system, weak part radiator, replace rad, upper /lower hose. thermostat, flush block, so what did I learn, just because I flushed the engine block out doesn't mean it's clean, new fluid and working like it should is going to "stir up" left over sediment(s), where is that going, heater core!!! What a dumb ass, totally forgot about that in the cooling "loop"!!! So I'll be flushing the heater core, and from driving it hard I now have a intake manifold leak to fix. Thanks guys for the help with this, here are the photos, maybe this will help somebody else out with the same problem. 1st driver side 2nd behind dash at ashtray 3rd Pass. side @ very bottom as is the 4th photo of the "flapper door".

 

[TechNova]

Flush your entire cooling system including removing the block drains. I had alot of rust in the bottom of the block that was stirred up from a coolant change and plugged the heater core. Amazing how much crap came out of block drains and knock sensor