When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Ok, its been a while since I replaced the heater core on my 70 supreme convertible, 350, no A/C. With the weather warming up, I decided to finally contort myself and connect the cables for the baffles under the dash.
With the inner box already mounted, I see 3 cables from the heater control, yet only 2 places to mount them on the top of the inner heater core box.
Do I need to drop the inner box (URRR) to attach the 3rd control, or is it possible this OEM control was made for either A/C or non, and only 2 are connected without A/C?
Ok, its been a while since I replaced the heater core on my 70 supreme convertible, 350, no A/C. With the weather warming up, I decided to finally contort myself and connect the cables for the baffles under the dash.
With the inner box already mounted, I see 3 cables from the heater control, yet only 2 places to mount them on the top of the inner heater core box.
Do I need to drop the inner box (URRR) to attach the 3rd control, or is it possible this OEM control was made for either A/C or non, and only 2 are connected without A/C?
And this is why everyone needs a Chassis Service Manual.
Section 1 has the heater diagrams and shows that the third cable goes to the defroster selection lever, on the firewall side of the heater box, at the driver's end of the box. The non-A/C and A/C controls are completely different.
Hi Joe,
Thanks for the direction...
Did some more searching on this site and found a link to wildaboutcars.com where I was able to sign up, then download the chassis assembly manual in PDF format. Saw what you were talking about, tucked my head back under the dash, and away we go!
Yeah hope so, im dealing with same thing. The heater valve works since both supply and return pipe are hot, but get no hot air with control. So it may be the control, which i assume is supposed to open a door or baffle or some sort to direct air across the heater core. The cable is connected and moving not sure beyond that. The heater core may be suspect too if its clogged. Some fun eh.
Yeah hope so, im dealing with same thing. The heater valve works since both supply and return pipe are hot, but get no hot air with control. So it may be the control, which i assume is supposed to open a door or baffle or some sort to direct air across the heater core. The cable is connected and moving not sure beyond that. The heater core may be suspect too if its clogged. Some fun eh.
Do you have A/C or not? The A/C cars are vacuum controlled. The non-A/C cars are cable only. Non-A/C cars did not use a heater control valve. This is a case of it would have been better to start your own thread, since the OP in this thread from 2014 did not have A/C.
Maybe we are using different semantics; my car is the same as the Op, non a/c, which is why i posted a reply to inform another poster who brought up vacuum lines, that this non ac model does not use vacuum controls. My car does have what i refer to as a vacuum controlled heater valve mounted on the manifold, that the heater hose is connected to. Far as i know thats standard, not sure what you are referring to.
Maybe we are using different semantics; my car is the same as the Op, non a/c, which is why i posted a reply to inform another poster who brought up vacuum lines, that this non ac model does not use vacuum controls. My car does have what i refer to as a vacuum controlled heater valve mounted on the manifold, that the heater hose is connected to. Far as i know thats standard, not sure what you are referring to.
Do you mean one of these?
My understanding is that this valve closes at WOT (when the vacuum goes towards zero) to restrict the flow of hot coolant to the heater core to prevent the pressure from causing the heater core to leak or burst. I could be wrong on the specifics, but it is unrelated to the flow of air through your vents.
I didnt say my blower doesnt work, it blows fine, the problem is the air is not hot. And yes that is the device i referenced and yes thats what its for, it opens with vacuum and allows hot coolant to flow to the heater core. Since my hoses are hot i surmise that it works as intended. But i still dont get warm air through the vents just sort of tepid no matter where i set the control lever. I need to see if the door jammed and that fixes it.
I didnt say my blower doesnt work, it blows fine, the problem is the air is not hot. And yes that is the device i referenced and yes thats what its for, it opens with vacuum and allows hot coolant to flow to the heater core. Since my hoses are hot i surmise that it works as intended. But i still dont get warm air through the vents just sort of tepid no matter where i set the control lever. I need to see if the door jammed and that fixes it.
Sounds like the valve does work. And since both heater hoses are hot, it sounds like the heater core itself is probably fine and not clogged. You are doing the right thing using the process of elimation. Good luck finding the issue.
My understanding is that this valve closes at WOT (when the vacuum goes towards zero) to restrict the flow of hot coolant to the heater core to prevent the pressure from causing the heater core to leak or burst. I could be wrong on the specifics,
The vacuum signal for the HVAC system doesn’t change at WOT due to the vacuum reservoir on the firewall - it has a check valve and maintains the vacuum when the engine vacuum decreases.
The thing that prevents blowing out the heater core is the 1/4” restriction in the base of the heater valve on AC cars and the hose nipple on non-AC cars.
Which brings us to this: non AC cars do not use the vacuum controlled valve. They use a restricted hose nipple.
Another thing to be aware of is there are two versions of the vacuum heater valve. One is normally closed and opens with vacuum applied, and one is normally open and closes with vacuum applied.
Maybe we are using different semantics; my car is the same as the Op, non a/c, which is why i posted a reply to inform another poster who brought up vacuum lines, that this non ac model does not use vacuum controls. My car does have what i refer to as a vacuum controlled heater valve mounted on the manifold, that the heater hose is connected to. Far as i know thats standard, not sure what you are referring to.
One more time. The heater control valve was NOT used on a 1968 Cutlass with heater only. It was ONLY used on A/C cars. Read the factory Chassis Service Manual. Since the heater control valve is vacuum operated, and the non-A/C heater controls are NOT vacuum operated, how would they operate a heater control valve.
Does your car have an engine swap? Perhaps an intake swap? Is the alternator on the passenger side or the driver side? In any case, the heater control valve is NOT correct for your car and should not be installed. That's your first problem. The second problem is to find out what else is not correct for a heater-only car.
Yes it is not the original 1968 350ci. I traced the numbers for the block to a 1977 and intake 1974-77. The engine does have the vacuum controlled valve on the heater supply. The vacuum hose supplying this device comes from a nipple directly from the top of the manifold behind the carburetor, not from the vacuum canister. The same manifold nipple branches off and supplies the vac canister and the transmission. Not saying thats right or wrong just thats how its hooked up. The only thing on my vacuum canister is the trunk lock release. Assuming this was operating as intended, at WOT there would be no vacuum and no heat. I dont see the down side of that since im not cruising at wot ever, even if that was the not intended operation. Do you think its required to have it hooked up to a vac cannister? I could do that easy enough.
Again i should be getting hot air with control set to warm and im not at present. The associated control cable moves but not sure what the cable is supposed to be moving since its hidden. My 68 cutlass assembly manual doesnt show it but its not totally complete either. I’ll try to locate that information.
Thanks for the input sorry for the confusion.
Using the vacuum operated heater control valve with a hose to manifold vacuum is kind of silly. Just replace it with a heater-only nipple. The main downside is that the valve is a potential leak point - the seal around the vacuum actuator that operates the valve is prone to failure. Plus, it can corrode and stick in position. Why keep it?
Temperature is controlled by the blend door, which is operated by the cable connected to the TEMP lever.
So you have a 1977-era heater valve that is connected to a constant vacuum source. Your problem is the heater valve is normally open and vacuum closes it.
I understand what you are saying but my heater hoses are both hot so coolant is flowing to the heater core which indicates the valve is open. Apparently this valve is an earlier version that opens with vacuum. Not sure why you would have a valve that shuts off the heat flow with vacuum, must be something else to it for some reason.
Not sure why you would have a valve that shuts off the heat flow with vacuum, must be something else to it for some reason.
As said previously, there are two heater valve designs. The early style is normally closed and opens with vacuum application, and the later one is normally open and closes with vacuum application. The HVAC control design was changed somewhere around 1971 or 1972, which is why there are two different style heater valves. Since you have a 1974-1977 intake manifold, you have the later style heater valve - the threaded section of the valve is a different diameter between two styles so they do not interchange (Opening B in the info below).
Thanks; i just looked closely at the valve and it has a 3/4 to 1/2 threaded adapter on it so the earlier version ( open with vacuum) can be installed on the manifold. Good to know, I'm going to pick up a spare one so when this one goes i can plug the new one in and not go crazy looking.
I think my no heat issue is related to a none operating blend door. Either the cable attachment broke or came off im guessing. Got to figure how to get to it first and see.
Thanks; i just looked closely at the valve and it has a 3/4 to 1/2 threaded adapter on it so the earlier version ( open with vacuum) can be installed on the manifold. Good to know, I'm going to pick up a spare one so when this one goes i can plug the new one in and not go crazy looking.
As Joe already said, get rid of the vacuum valve and install a restricted nipple.
Originally Posted by joe_padavano
Using the vacuum operated heater control valve with a hose to manifold vacuum is kind of silly. Just replace it with a heater-only nipple. The main downside is that the valve is a potential leak point - the seal around the vacuum actuator that operates the valve is prone to failure. Plus, it can corrode and stick in position. Why keep it?
If you feel you must use a vacuum operated valve, remove the adapter and use the valve that directly fits the manifold and doesn't need vacuum to open, and leave the vacuum hose disconnected. But that just ends up being a restricted nipple...
Looked into this as much as i could. It appears the vacuum controlled heater valve on my non ac car was only used on a/c cars. Or to when they changed to vacuum controls for the heater only cars too ( not clear about that). The 68-70 non ac cars used a 1/2 inch threaded fitting straight from the block and 71-74 used a 3/4 inch. Havent determined or looked beyond that.
so with respect to my 1977 350 engine with a 1968 heater. I have no idea what the 77 engine had originally but its a 3/4 threaded opening. I found the 3/4” fitting on Fusicks that will fit, so im getting rid of the control valve thats on there that is not right for the application and going straight to the heater.
thanks for everyones input; for me it was difficult trying to rationalize why things were installed, thinking who ever put this together did it right.
. Hey it may work but didnt make sense.
