Heat is turned off but it’s still heating?
 

Good Afternoon all,

My 66 vert still has heat coming in even though I have the heat knob all the way in?
New heater core and new radiator just installed.

Any ideas on what I need to tackle to resolve this issue ?

Thank you in advance
Joe

Pull the heater box out and put all new seals on the flapper doors

Is the heater valve installed, and working correctly??

that is if he has factory AC

Well, you realize there’s flow running through the heater core at all times right? Then it’s just a matter of damper position adjustment, and damper sealing surfaces, as was suggested..... you need to take a look

Is it blowing hot air when you're sitting still with the fan running or just when you're riding down the road?

When going down the road mostly

No A/C Car

I can only guess how big of a job that is ?.
Sadley when I replaced the heater core I had no idea what did or didnt work as I bought the car with the heater core bad and bypassed, It came with a new GM heater core. Good news is when I went for a top off ride today it was quite chilly we had heat

The hose will be cool on the heater side of the valve.

I have this same situation. I did the same as you, when I got my car the heater core was bad and bypassed. I also put a new core in but now it’s putting out heat when shut off. I am going to put a brass mechanical shut off ball cock on the pump output to shut down flow to core in summer. Then I can open it fall and spring. :thumbs:

try a shut off valve ....splice into heater hose to stop the hot water from circulating

Grainger Shut Off Valve
 

Take a look at post #4 and #7 and #12 in this thread:

https://www.corvetteforum.com/forums...r-shutoff.html

I installed that over 5 years ago and it makes a big difference in the amount of heat that comes into the cockpit. Works good and lasts a long time. Good luck!

Thomas

It's a totally different issue if the heat is coming in only when driving. If you're feeling hot air coming through the heater vents with the fan on, even sitting still, then I would add a shutoff valve as described earlier. I have put one on every non-air C2 and C3 I have owned and shut off the hot water to the heater core in warm weather and turned it back on in cold weather. I buy mine at Lowe's for around 10 bucks. The handle is held on by one screw, so I take it off and put it in the glove box. You don't have to put the screw back in to use the handle. I also paint the body of the valve flat black so that it is hard to detect. I usually put them at the input to the heater core at the fire wall, but have put a couple in line at the water pump. Be very careful about pushing and pulling on the inlet tubes to the heater core, I learned the hard way that it is not all that hard to crack the weld and create a leak that requires pulling the heater core. Use a knife to cut the hose off the tube if it is stuck. IF you want to see if that solves your problem first, just pull the two hoses and connect them together to completely bypass the core. If you're still getting hot air, see the second possibility below:

IF the hot air is coming in during driving (specially with the heater core disconnected) you may have an air leak around the firewall at the fenders. One of my cars had had the front end replaced and they did not seal the junction where the firewall meets the fender with the black stuff and in summertime the hot air blew in from the engine compartment and was very uncomfortably hot. If that is the issue, the hot air comes in around your legs at the kick panel and not out of the heater ducts

So, first determine where the hot air is coming from before you pull the heater box again. If you never need the heat, you can block the two heater hoses to stop coolant from ever reaching the core and if you want it to look correct, connect the blocked hoses to the heater box tubes under the hood. They can be blocked inside the hoses leaving some space at the ends to reconnect. If the hot air is coming out of the heater vents, anything to keep hot coolant from circulating into the core will help tremendously.

PS You said new heater core, so also make sure the heat cable is connected correctly and the door in the box to select air direction is moving when you push/pull the heat switch.

Nice description from JohnZ:
https://cimg0.ibsrv.net/gimg/www.cor...44a7139773.jpg

My bad. You only have a valve if you have an AC car. Heater shutoff has everything to do with the seal on the flappers.

Until you have the energy to remove the passenger side heater box to check the directional flaps and gaskets, I would install a small gate valve (post 12&13) off your intake manifold on the inboard heater hose. That will cut off hot coolant to the heater core. I have done this on all my C2 Coupes even though they work correctly......It will help to eliminate heat......
https://cimg5.ibsrv.net/gimg/www.cor...d5d00ee83d.jpg


https://cimg7.ibsrv.net/gimg/www.cor...70defc15a8.jpg

I am tackling my heater box as we speak. Because it's a project car, I have everything out and apart and have pics of just about everything involved. If it helps, let me know and I'll post pics of whatever you need as best I can.

Now - I have a question on mine. Hopefully this will not be considered a hijack, as the OP may elect to rebuild his and this is the crux of it. I have a heater seal kit which includes everything you need for sealing all the components. The seal for the defroster "door" is a block of rubber which I believe I can remove the old with a putty knife, and install the new with...weatherstrip adhesive? Or use something else? Looks like I can do that without taking the door out.

https://cimg4.ibsrv.net/gimg/www.cor...7c5b0e0224.jpg


At the other end, the "door" to shut off or allow airflow - which seems to be part of OP's problem - has 2 pieces of peel-and-stick rubber which I presume go one on each side of the door. Can the back side of the door be left un-sealed? I'd really rather not get into drilling out the rivets and removing that sheet of metal. It seems if the seal closer to you can be put in place after a good cleaning, it will seal off heat and prevent OP's problem. The worst that would happen the opposite way is a little outside air may get by and slightly diminish the heating EDIT: OK, thanks to the drawing in Post 15 I found the third door. Man, they don't make it easy to find, do they? :lol:

https://cimg6.ibsrv.net/gimg/www.cor...a82fb4a04e.jpg


Lastly, for anybody doing this I'll state the obvious. Be sure to free up and lubricate the heat control and the defrost controls on that inner heater box - it was amazing how stiff they moved before and how easily after I worked on them. And at the same time, lubricate the pull cables that go to the knobs you use to move them - those cables also had a lot of resistance which a little lube and back-and-forth took care of. I'm thinking that once this is all together, the heater and defroster "should" work pretty close to like new.

Is the heater temp cable hooked up properly?

Tom

As always, the Vast knowledge base here on this forum has once again solved my issue.

As BB767 pointed out by referencing posts #4, #7 and #12. These certainly went a long was in resolving my issue.

Thank to everyone who offered their knowledge. Much appreciated.

Joe