No Heat?

[samwise68]

hey all,

first. i have searched. but was hoping i could find a more specific answer to my question.

on my GMC, there's very little heat. and, since i live in Wisconsin, this is a problem. lol.

after letting it idle for about 10-20 minutes, the vents just don't blow much heat.

the heater core is fine, as both hoses coming to and from are warm to the touch.

so, what can i kinda look at to be the culprit?

a resistor? a bad relay? control panel not opening up all the way?

any ideas would be great.

thanks all!

-Sam.

[Longhorn Man]

is the problem low air temp, or is it low air flow?
Have you run it longer than that? Tried driving it?
Coolant level good?

[Stocker]

What thermostat are you running? You say the heater hoses are warm to the touch, but they should be hot.

[jrdv]

I had the same problem. I switched the hoses and ran the coolant backwards for a short time. It worked-I think the core can get plugged with junk sometimes.

john

[cdowns]

sometimes the heater core is plugged up with 40 years of pine neddles leaves and mouse nests causing no air flow over the heater core if thats the case you'd need to remove the blower and heater core and clean the crap out the box

[Premium72]

yup, i just re built all my heater componants, truck was out side for like 30 min or so an i can hear no i have a leaf in my hater box...YAY!!haha..

[jgrh64]

if your truck is a A/C equipped truck make sure all vacuum lines are attached , in good condition and hooked up correctly and all vacuum diaphrams are still working -mine was a mess

[72armyswbtruck]

Leaves are almost always the culprit

[70GMCer]

Just replaced my core and for the second time, MICE nests in the duct work and housing. Cleaned it out and also replaced my blower motor and wheel from a 90's crewcap truck. This thing blows some air now......

[xtreme80]

I wanna go ahead and chime into this one as well. I posted nearly the exact same topic in the 73-87 forum and didn't get much of a response.

I have a factory AC truck, and the AC blows cold and blows hard out the vents. The heat, on the other hand, barely trickles out. It's really hot, just doesn't have the flow.

Where is the heater core? I'm not much of an HVAC person.

[cdowns]

follow the heater hoses from the engine the other end is hooked to the heater core

[beautimus]

As one of the guys above stated, it can also be the water side. if you have plenty of air flow and the air is not hot, then the heater core may be plugged up. i have ran into this myself. when the heater is turned off, the heater control valve shuts down the flow of water through the heater core to keep from roasting you during warm weather. so the stagnated warm water begins to let the disolved minerals drop out and deposit on the interior surfaces of the core. given enough time this can totally block the heater core.
another factor is the use of "bars leaks" this is a product that is sold in a lot of auto parts stores that can effectively plug pinholes in radiators. this stuff will get you home but if you use it, you need to flush the cooling system and change the coolant afterwords. i have repaired this issue on several cars by simply using radiator flush and new coolant.
the next culprit is the thermostat. if it sticks in the open position, the water may never get hot enough to heat the core properly. in other words the water does not stay in the engine block long enough to capture all the heat that it can, before it goes to the radiator and gets cooled off again.
Good luck! Tony

[retodd7711]

do you have a temp gauge? It should be running 170-180 degrees. If not a stuck thermostat is the cause. Do you have air flow from the vents?

[Stocker]

What about no thermostat? That could do it too...

[72402]

Might just need a new thermostat. I have to run a 195 degree in mine or it won't defrost the windshield.
Frank

[samwise68]

wow, thanks for all the responses guys!

unfortunately, i haven't had a chance to drive it yet. the longest i've had it run is the time it took to time it, idling in the driveway.

so, maybe its not long enough to get warm? idk.

i was just trying to nip the problem in the butt before i started to drive it avidly.

i'll look into these, starting with driving, and letting it run for a while, to see if that helps. which it really can't hurt.

after that, i can start to diagnose it further. but you all are probably right regarding pine needles and junk. so, i should prolly get on that as well...lol.

thanks guys!

-Sam.

[PanelDeland]

Also check to see that the heater control valve is actually opening.I had one that the heater temp control cable had slipped in the clamp so when you slid the lever over it just barely opened the heater control valve.The hose into the HC was warm but not hot.Once I figured out what was going on I reclamped the cable and all was well.

[Ilike 72"s]

Could be as simple as adding water if it's low. To low--won't flow! Good luck

[nightmare]

Originally Posted by PanelDeland

Also check to see that the heater control valve is actually opening.I had one that the heater temp control cable had slipped in the clamp so when you slid the lever over it just barely opened the heater control valve.The hose into the HC was warm but not hot.Once I figured out what was going on I reclamped the cable and all was well.

do you have a picture of this area? i think that mine is doing the same thing. not only that, does anyone have a vacuum diagram that i can reference for the vacuum hoses?