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Heater Problem--No Heat

mtnman210

mtnman210

1/2 ton status
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the heater in the blazer was wokring fine and all of a sudden I only am getting cold air. The blower works, it's pumping air, it's just COLD. Also with the heat/air controls on off if I move the switch to hot it takes a long time to get any warm air in, If it gets any. I don't know if it's realted, because I think I'm just out of freon, but the AC isn't blowing as cold as it should. But like I said I think I'm out of freon.

I've check fuses, and all the connections on the heater and can't find anything. What could cause the blower to still be fine but I'm not getting any heat out of it?
 
is there antifreeze in your radiator? the truck uses this to heat the cab. check for leaks around the heater box or on the radiator
 
It sounds like there's a problem with your main heat mixer door, which is vac-operated. Trace your vac lines and see if something's been disconnected.
 
First make sure that the heater box trap doors are working correctly, if that is ok then check fluid level in the cooling system. If cooling system level is fine then i would suspect a plugged heater core.
 
or a bad heater control valve, the valve inline with the water that controls the amount of water getting to the heater core...
 
I've never seen a heater control valve on a gas powered Chevy ever. Fords used them alot and i've had Fords with them but never seen one on a Chevy.
 
4X4HIGH said:
I've never seen a heater control valve on a gas powered Chevy ever. Fords used them alot and i've had Fords with them but never seen one on a Chevy.
Click to expand...

Then how do you expect the temperature to be adjusted from cold, to luke warm, to warmer to hot,,,,this valve is on EVERY SINGLE 80's model Chevy i have ever owned. It is operated either by a cable lever, or a vacuum switch through the control panel on the dash (temp selector)

It adjust how much hot water flows through the heater core,,,,

this pic is the one on my 89 Suburban, this is not the stock one,,,the stock one had 4 ports to accomodate the rear heater as well.

I do believe however there is a new version, mid to late 90's on up, controlled electronically through the dash controls.

heater control valve.jpg
 
yeah Ive never seen one either. Ive owned 3 and worked on at least 5 others and none of them had one.
 
That is definately a heater control valve, but not on my factory 1989 blazer, nor my old 1976 blazer, nor on my buddies 1988 blazer, shall i keep going?
 
so you guys just run with heat all the time then huh,,,or do you expect the "blend doors" to adjust the heat with some cold air from outside,,,,hmmm, weird, oh well, again, i don't know sh!t here, just babbling on about things that were NEVER on a Chevy..

Have fun

EDIT : this was worded weird, sorry :doah: :crazy: :o
 
Last edited:
4xcrazy said:
so you guys just run with heat all the time then huh,,,or do you expect the "blend doors" to adjust the heat with some cold air from outside,,,,hmmm, weird, oh well, again, i don't know sh!t here, just babbling on about things that were NEVER on a Chevy..

Have fun
Click to expand...

For the record, i did not say they were NEVER on a Chevy but rather I'VE never seen them on a Chevy. My blazer is bone stock as far as the A/C-heat is concerned and my 1989 blazer NEVER came with a heater control valve inline with the heater hose as you've pictured. My heater hose goes from the intake manifold to the heater core directly and the other hose goes from the heater core to the radiator directly with nothing inline with either hose.
 
Sorry, don't get me wrong, i am just seriously confuzzzed, i keep hearing about people NOT having these valves on their trucks or whatever, I haven't seen them without them, so i am not sure on how a system without the valve, is supposed to work i guess..., i know if i remove mine, and all others in the past i have owned, i get nothing but hot air,,,all the time :confused:

anyways, we kinda got off the topic originally posted, so anyways,,, :p:
 
I'm sure there must be something different about the A/C-heater suit case or trap door configuration between trucks that use the valve and the trucks that don't.
 
you know some people are baffled about this, when you receive international phone calls aboot it :doah: :p: :D

i know i am, :crazy:
 
Okay, TJ. As promised, here are the pics of my heater hose setup.

1. Here's a pic of the hoses going into the heater core:

IMG_0278.jpg


2. This is one of the heater hoses coming out the manifold:

IMG_0279.jpg


3. And here's the other hose coming out of the rad itself:

IMG_0280.jpg


You'll notice the lack of a heater control valve anywhere in the system. The heat or lack thereof is controlled by a blend door. FWIW, all three of my trucks has the exact same setup.
 
All of the 80's era trucks I have seen haven't had the valve on them the mixing is accomplished with the doors in the interior duct box. My IFS era rigs all have that valve though. I recently went hunting for some heater boxes and I know that valve wasn't present in the systems at the yard about 20 or so trucks.
 
again, i am not sure why this is so weird, i even looked up one at Autozone awhile back, and they carry it, have it in stock listed for my year of truck and all....

Mine is a factory setup, even has the vacuum hose coming out from the firewall to supply the controlled vacuum to the valve.

I have taken this out once, and run the hoses directly, and i get nothing but scorching heat, will not cool down...

again, weird,,,i dunno
 
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