99 chevy 1500 heating issue

JasonWatts · **Posted:** Wed Nov 02, 2011 4:25 am

So my truck has apperently stopped making heat in the cabin. Everything sounds like it is blowing just fine. My initial thought is the heater core, but wanted to see if anyone else had other idea's before i start to source one.

DickRasmussen · **Posted:** Wed Nov 02, 2011 6:25 am

I don't know chevy's but I would look for a water control valve and a blend air flapper. There may be a disconnected mechanical or pneumatic (air/vacuum) actuator of some sort. I don't know why the heater core itself would be the problem. Is the engine warming up per the gauge? If not T-stat?

Our Dodge truck uses vacuum to control air flow through the core but the "fail safe" seems to be to heat/defrost. It also has a water valve for the heater core. Ours is very obvious since it sits over the top of the engine (van).

Dick

Vincent Keene · **Posted:** Wed Nov 02, 2011 8:43 am

T-stat would definitely be the first thing to check.

Bernie Baake · **Posted:** Wed Nov 02, 2011 9:01 am

Heater cores don't fail by not giving heat, they fail by leaking.....It's more likely to be what Dick and VK are talking about...Loss of coolant flow to the heater or blockage of air to or from the heater core. First thing to check is that the coolant level is proper. routing of the heater hoses oft times creates air bubbles that settle in the heater or high spots created by the hose. So make sure the engine is full of coolant, then find where the hoses penetrate the fire wall and check that both hoses are hot when the engine is hot. If they are then your problem is in the air ducting. If they are not both hot then you have a coolant flow problem.

JasonWatts · **Posted:** Wed Nov 02, 2011 9:34 am

Thanks all. My initial thought was the heater core due to me loosing the it inis my old ranger. But i also had the smell of coolant in the cabin.

The engine is getting up to its regular temp according to the guage on my dash
I will check for the hoses and see if i can find them and start there.

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

I wouldn't put too much faith in the stock temp gage; the difference between "warm enough" and warm enough to produce hot air can be significant. I was freezing last week while the gage was just shy of 1/2 way. A simple thermostat swap and I'm warm again, and the gage has barely moved.
Charlie G

Michael Westerfield · **Posted:** Sun Nov 06, 2011 11:48 pm

Similar to what Dick and VK suggested, I've had a car that valve got "stuck". After I hit the mechanical assemble with some WD40 and moved it back and forth with my finger a few times I had heat again.

JasonWatts · **Posted:** Sun Nov 20, 2011 10:46 am

ok, so I have done some more poking at this and have a few more symptoms that have me not thinking its thermostat.

~Truck arms up quickly. ~10 min to get up to 210 with a small pause halfway along. I believe the pause is the thermostat opening up?.
~the hoses leading to the FW. one is hot, the other is somewhere between warm and cold. My interpenetration of this is hot fluid flows into the cabin, but never flows out. the heat I am feeling is just soak from the other hose/warm engine bay. Is there another explanation?
~ The heater now produces small amounts of heat. Its possible that it was doing it all along and minor heat in 20 degree temps feels similar to no heat. If I put the blower on 2, it will pump out nice warm air for about 30 seconds to a min before it goes to lukewarm at best. HOWEVER this morning, I was able to crank it up to full blast and it still produced heat, though it was not much warmer then outside air.
~ No leaks or smell's of a leaking Heater core. Fluid levels look fine. (over flow was full)

So, right now I am wondering if the 1) the heater core was completely clogged and has since become only mostly clogged. or 2) there is something else inside the cabin related to the heating system's fluid route.

all I know is I really hope its not the core. my week googlefu search does not reveal any diagram's of the system, but it does however say I need to rip out practically my entire dash to replace the heater core.

JamesShort · **Posted:** Sun Nov 20, 2011 11:56 am

JasonWatts wrote:

My interpenetration of this is hot fluid flows into the cabin, but never flows out.

I thought Stephen W had a wrap on THSCC Forum Quote of the Year with his comment about Rodney and Les getting Prii.....but that might take the cake :mrgreen:

JasonWatts · **Posted:** Sun Nov 20, 2011 12:09 pm

JamesShort wrote:

I thought Stephen W had a wrap on THSCC Forum Quote of the Year with his comment about Rodney and Les getting Prii.....but that might take the cake :mrgreen:

I always try and impress. sometimes I succeed.

jeremy gast · **Posted:** Mon Nov 21, 2011 9:41 am

you need to look at the adjustment on the cable from the heater controls to the blend door, even on high it might not be opening the door all the way on the box!!!

JohnByers · **Posted:** Mon Nov 21, 2011 10:38 am

jeremy gast wrote:

you need to look at the adjustment on the cable from the heater controls to the blend door, even on high it might not be opening the door all the way on the box!!!

This times 11ty billion

:soap:

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