No heat and I think I've tried everything...

[jonrbrt]

I have a 72 K10 Cheyenne Super with factory air. Always had good heat. Last summer I had to replace a broken defrost lever. Now I have no heat. Here's what I've tried.
1) Noticed water was hot on both sides of heat air control valve.
2) I suspected it could just be heat transfer and not really getting through--so I by passed the valve--still no heat.
3) Next I replaced thermostat with new 195. and while I had coolant drained, I also opened hoses to heater core and simply stuck a garden hose nozzle to one side to make sure water flowed through freely. It did. still no heat.
I get plenty of air through all vents defrost, AC or floor all levers seem to be funtioning correctly--plenty of air--just not hot.
what does inside air and outside air mean on top lever? Where does outside air get in... is it through the cowl?
With the truck in the garage and warmed up it will blow heat... but as soon as I start moving it gets ice cold. Even the box the heater core itself is in is ice cold. What can be going on?

[kwmech]

Huh?

Hey we have text now. In additon to the responses below, take a look at the vac source in the engine compartment, both to and from the vac reservoir

[HuggerCST]

Did you reconnect the 2 vac. hoses to the a/c control? The inside/outside air lever controls vacuum to the cowl flap, heater valve, and right kick panel fresh air vent. It gets fresh air through the cowl.

[HuggerCST]

This may help.

[Hottrucks]

does the lever move under the hood on the top of the heater box sounds like its just blowing though the A/C box and not going though the core...the one the cable is hooked to??

[Indyuke]

My defrost lever broke one time and I had the same problem you're having. It turned out I had the vacuum hoses switched around on the "control head vacuum switch". The hoses each need to be on the right nipple, because one has a bleed off hole to release vacuum and the other doesn't.

[jonrbrt]

yes one of the levers(I dont remember which one) does move a lever on a vacumm looking can on top of the passenger side firewall. I do remember hooking up the vacuum hoses on the control head vacuum switch... I have to recheck that--I dont recall marking where I pulled them from--guess I didnt think it made any difference. Sounds like the first place I need to look. How much vacuum should be on those hoses? It feels like none while the truck is idling....

[cdowns]

have u tried flushing the heater core to see if coolant will actually flow thru it?

[Stocker]

Originally Posted by cdowns

have u tried flushing the heater core to see if coolant will actually flow thru it?

Originally Posted by jonrbrt

while I had coolant drained, I also opened hoses to heater core and simply stuck a garden hose nozzle to one side to make sure water flowed through freely. It did.

[haysonj]

There's a divert er flap in the divert er box which switches the air from AC to heat. these frequently break so the lever still moves but the flap doesn't that is most likely your problem

[jonrbrt]

To answer new questions--as said above I used a garden hose and flushed water through the core---seem to come out with the same pressure it went in. I have had center S plastic out and I can see the flap in the diverter box moves freely. The diagram Huggercst provided is great but my Control vacuum switch has 3 ports and 3 lies running to it??? What's up with that? Mine is a 72 Cheyenne Super... are there differences between models?
I've switched the 3 lines on the ports in about every different combination but still no heat. How much vacuum should be on this thing--I cant tell there is any on mine.

[mikemileski]

To answer your comment about having three ports, here's what 71 super replied to me on a similar thread I started on vacuum hose routing last week:

"You will have a line from #1 port located on heater head unit to reservoir, and #2 will tee if early head unit , one side coming off of tee will hook to fresh air vent on passenger kick panel, the other will enter engine compartment and tee again one side to actuator on firewall for fresh air on kick panel and other the heater cut off valve in passenger inner fender. If you have a later three prong valve on head unit you will delete one tee from previous assembly and continue as above."

Hope that last part helps you.

Mike Mileski
Tucson, AZ

[Stocker]

Dumb question maybe, but is the coolant circulating? You should be able to remove the radiator cap and see it moving. If something like a collapsed lower hose (or a bad water pump) was preventing circulation, you'd have no heat due to no coolant flowing through the heater core. OTOH, the engine would likely overheat..... but maybe not, in colder weather.

I dunno, just clutching at straws here.

[HuggerCST]

Since yours is a 72, I just assumed that you had the 2 port system. Sometime around 71, GM changed to a 2 port system, but 67-70s had a 3 port system, or a 3 port "switch". The pic below is the earlier 3 port system. Notice the early and late style hot water valves work opposite, so your hot water valve should match the style of switch.
One of your 3 vacuum lines should have vacuum whenever the engine is running. It should recieve vacuum from the intake manifold, between the carb and distributor, but anywhere on the intake, or base of the carb should be fine. That vacuum line should run from the engine to the round canister mounted on the side of the outer a/c box, then from there to the a/c control.

[jonrbrt]

Thanks hugger for the 3 port diagram... not sure why my 72 would have the 3port if that's the older system but it definitely does. I will check routing tonight...
and Stocker probably not dumb at all. When I look in the radiator with cap off and truck running... I've thought to myself it doesn't seem like a lot of movement... but the fact that the truck dont overheat while idling even on warmer days we've had this winter amde me think it had to be circulating--but that could answer why I get heat while it's sitting still. If tracing the vacuum routing doesnt lead to anything... maybe I'll just replace the water pump.... I'm pretty sure it's a lifetime warranty from AutoZone--maybe that's the real problem...

[Brad]

I'm only getting lukewarm heat from my non-AC heater. Both hoses are hot, I've checked the door to make sure it closes fully, 195* thermo. The only thing I've noticed is that there are big gaps around the holes where the hose plug into the heater core. After reading the above about that, I'll tape those up temporarily to see if that helps. Any other suggestions?

[kevmic28]

I had no heat when my water pump was going out. Replaced it and its hot now.

[mrein3]

Do you 'burp' the cooling system when you re-fill it?

Put everything together and fill with 50-50 coolant and water until the radiator is full.
With the cap off the radiator and a drain pan on the floor under the open cap, start the truck.
Let the truck run until you see coolant flowing through the fins. The level usually rises, spills on the floor and makes a big mess. It then usually cycles between low in the radiator and then overflowing for a while as the thermostat opens, draws in the cold coolant, and closes again. Once it is good and warmed up - when you see a steady stream of coolant coming through the fins in the radiator, top it off, and replace the cap.
--system burped--

If you have flow through the heater core - you verified that with the garden hose, both heater hoses hot - you verified that, and the system is burped - no air pockets in the system, you have to look for something with the venting of the heat downstream from the heater core. Vent door not open, cowl flap stuck open letting in too much cold air, etc.

Maybe even something crazy like a mouse built a nest in the heater core box which then doesn't let any heat out of the core and into the passenger compartment.

[GASWAGON]

Check the positon of your heater hoses. One should go to the intake the other to the water pump. If you have one on the pump and the other goes to the radiator then your just running the recently cooled coolant through the core and then drawing it back to the water pump. I have seen this more than once. Just a thought.

[jonrbrt]

Now I have tried everything. I replaced the water pump... AND I STILL DONT HAVE HEAT. Heater hoses run from top of intake to core out core to water pump. guess I should mention again--I've owned this truck for 28 years and it always had plenty of heat. No heat only started this year after I replaced the Radiator with a new one from autozone (with plastic tanks) and removed the AC/heater controls to replace a broken defrost lever. I did remove the 3 vacumm hoses but I marked them with tape to remember how to re-assemble and I have verified correct routing with diagram provided. The only thing I question now is... There is a door (flap) under the cowl on the passenger side. it is hooked to a small vacuum canister. That flap never seems to move. It is resting in the up position. I've disconnected it from the vacumm linkage and it goes down a little( which I think down is closed) but that still doesnt help. And as far as mouse nest, door/flap not opening... I have had the box apart inside. The "S" duct heater piece out. I can reach in and tocuh the heater core and with the truck wamred up, while hot... it doesnt seem all that hot to me.

[Jacfourteen]

Originally Posted by jonrbrt

Now I have tried everything. I replaced the water pump... AND I STILL DONT HAVE HEAT. Heater hoses run from top of intake to core out core to water pump. guess I should mention again--I've owned this truck for 28 years and it always had plenty of heat. No heat only started this year after I replaced the Radiator with a new one from autozone (with plastic tanks) and removed the AC/heater controls to replace a broken defrost lever. I did remove the 3 vacumm hoses but I marked them with tape to remember how to re-assemble and I have verified correct routing with diagram provided. The only thing I question now is... There is a door (flap) under the cowl on the passenger side. it is hooked to a small vacuum canister. That flap never seems to move. It is resting in the up position. I've disconnected it from the vacumm linkage and it goes down a little( which I think down is closed) but that still doesnt help. And as far as mouse nest, door/flap not opening... I have had the box apart inside. The "S" duct heater piece out. I can reach in and tocuh the heater core and with the truck wamred up, while hot... it doesnt seem all that hot to me.

How does the temp run? have you checked the thermostat? Maybe it's stuck open, and running cool. Other than that I can't think of anything. Good luck.

[Jacfourteen]

Originally Posted by jonrbrt

3) Next I replaced thermostat with new 195.

Sorry I missed this the first time I read it, but still check the temp because the quality of thermostats isn't all that great nowadays. I usually buy two or three of them and boil them in a pan with a thermometer to see which one opens the best so I know for sure that it works.

[HuggerCST]

If the cowl flap isn't closing when vacuum is applied, then 1- something is physically stopping it, 2- the vacuum pod has a leak, or 3- you have weak vacuum (leak somewhere). Weak vacuum will cause the hot water valve to not open all the way, or not stay open, and engine vacuum is strongest at idle, so it may be that the vacuum is getting weak when you drive, closing the hot water valve. Try watching the hot water valve when you turn the heat on. Is it opening? Does it stay open when you rev the engine?

[jonrbrt]

Right now to remove the heater control valve from the equation--I by passed it. I just put a hose connector right beside it and by passed it. So I know it's opening. I guess the only way to get to this flap is to remove the cowl vent body panel? I had it off years ago when I painted the truck--I think it's just a matter of removing a couple of screws and the wiper arms isn't it?

[Hottrucks]

ok I didn't go back and read all of the post but the heat system is so simple it can only be a few things heres the order I would check them based on your heat valve being by passed

are both hoses hot?? if they are then its a vent issue if not no use looking any further...If the heater core is full of poop then its not flowing ...no hot water out means no hot water in...to fix it I would pull the hose off that goes to the top of the heater core and pour in some CLR and let it work its way though ( if it flows slowly hold the lower hose higher and let it sit in there for a 20 min or so) the other hose goes in a bucket to recycle it though a couple times...after you have done that place a gargen hose on the lower hose and back flow it till it runs clean and flows well hook up the hoses fil it up and conferm that you have hot in and out....

second..if the heater hoses are both hot that mean you have good flow..check your flaps and fan ...the vent in the cowl can be un hoked and done by hand...if the flap is broken you should be able to feel nothing when you move the lever manually..because it will just go around in circles....if its broke then chances are it fell to the bottom of the cowl anyway ( you may be able to see it though the inside floor vent??) if the flap is stuck closed by openig the floor vent on the PS it will suck air from inside the cab back though the heater core and you should have heat that way

check these things out and I'll check back..I'm going to read back ont his post to see if I missed something but like I sad heat is so simlpe it can only be 1 or 2 stupid things...and I'm assuming you checked the thermostat and that your water pump are ok