No heat...Help!

No heat...Help!

Postby Leeward [OP] » February 18th 2021, 3:35am

I just bought an 2005 Astro 4.3 RWD. No heat, first thing was to replace t-stat which was definitely stuck open. Filled & bled system, still no heat. Replace Heater control valve no help. Changed the water pump, no help. Flushed the heate core, no help. The larger hos to the heater core gets hot,seems like coolant is not flowing throught the core. I confirmed both hoses to the heater control valve are hot. Not sure what else to do. Tried to bleed with RF tire jacked up ....no help
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No heat 2005 Astro 4.3

Postby Leeward [OP] » February 18th 2021, 4:17am

No flow through heater core, changed all major parts still no help. Flushed Heater core as well. Larger hose gets hot but does not flow through core. Tried jacking up the passenger side to get air out...no luck. Anyone know way may be causing flow issue?
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Re: No heat...Help!

Postby SportsBoy » February 18th 2021, 2:18pm

I am not a heater core expert, but....

When you flushed the heater core, did it flow fine when flushed in both directions?
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Re: No heat...Help!

Postby Leeward [OP] » February 18th 2021, 2:44pm

Yes, flushed both ways totally clean
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Re: No heat...Help!

Postby tungtide » February 18th 2021, 3:59pm

Try looping around the heater core. See if the loop hose gets hot. Both ends. Just did a ford truck even though the core seemed ok it was not.
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Re: No heat 2005 Astro 4.3

Postby Sailing_Faith » February 18th 2021, 9:05pm

Sounds like either a bad heater control valve, no vacuum to the heater control valve, or sludge in the heater control valve.

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Re: No heat...Help!

Postby AstroWill » February 18th 2021, 10:48pm

Low vacuum to heater valve, or maybe the valve is broken/clogged.

Just be careful if you touch the valves, they get extremely brittle over time.

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Re: No heat...Help!

Postby Leeward [OP] » February 18th 2021, 11:15pm

So I also changed the heater control valve no help. the smaller hose is not getting hot. Seems as if the coolant isnt pushing through.

When I first filled it and bled it out I had heat for 3-4 minutes then it just went cold
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Re: No heat...Help!

Postby The Drummer » February 18th 2021, 11:27pm

I think that by default the heater valve will be open if no vacuum is applyed to it , try disconecting the vacuum hose that goes the heater valve , also if i recall ,you may activate the heater valve from underneath ,smal push/pull thing , i am not sure tho .
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Re: No heat...Help!

Postby Leeward [OP] » February 20th 2021, 12:23am

You are correct, by default there is no vacuum to the Heater Control Valve until the A/C is turned on.

Tried with & without vacuum, no change...still cold. I confirmed there is no coolant in the oil , truck runs great otherwise and I know the t-stat is functioning properly.
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Re: No heat...Help!

Postby Mmusicman » February 20th 2021, 2:33am

Hate to ask a dumb question, but are you sure the heater hoses are hooked up to the engine correctly?
It's pretty hard to believe there is NO flow though them... (unless both sides are hooked to outlets)

Heating is pretty simple...
1) hot water flows though coil,
2) air blows across coil.
Find out which is your problem, and go from there
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Re: No heat...Help!

Postby The Drummer » February 20th 2021, 3:05am

If you run the engine with the heater core inlet hose disconected coolant should be flowing outa there , i would think no , because you said that you are able to run flow thrue the heater core , but if yes then heater core is clogued , if not then the new valve maybe faulty , if not bipass the heater valve and run from engine direct to heater core inlet and see what happends , i am no expert but like MM said , either the core is clogued or you have no coolant flow , also keep in mind that a dirty heater core wont give you heat even with the inlet hose hot ,on mine its how it was ,very little heat and you could not hold the hose for it being too hot , i flushed the core both ways many times and voila you could not hold your hand to the vent long , it works for a few months ,i had to flush it every fall , haqd i kept the van i would of install a new one ,it gets cold here and besided ,replacing the core on these vans as to be one of the easyest to replace , at least in any vehicle i ever worked on , use a cheap oven thermometer in the vent ,you should not have that many degrees differences between engine temp and vent temp ,
also it maybe a dum question but , are you sure that the trap door works from cold to hot on the controls from the dash ? .
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Re: No heat...Help!

Postby AstroWill » February 20th 2021, 3:51am

Leeward wrote:So I also changed the heater control valve no help. the smaller hose is not getting hot. Seems as if the coolant isnt pushing through.

When I first filled it and bled it out I had heat for 3-4 minutes then it just went cold


Is the cooling system properly bled? Have you been driving it? If the hose isn't getting hot, it's not getting flow. Maybe an air pocket? Personally I haven't had that issue, I usually park on my inclined driveway and it goes easy for getting the air out.

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