[Fun 71]

I have a 71 Chevelle with factory AC. I am in the process of putting the entire system back together, and have been trying to determine how my heater bypass control valve should be installed. To eliminate the valve in the intake manifold, I am using the heater control valve for a 70 Chevelle, mounting it on the inner fender well, up close to the passenger side hood hinge. I have checked out the vacuum line to make sure it works.
Now that the valve is installed, when I start the car up, the temperature will climb to well over 200 degrees, and as soon as I put the control setting inside the car to heat, AC, Max, etc. the coolant temp drops right down to 180 or less(running digital gauges), but I of course have hot water in my heater core, which is what I am trying to eliminate.

I have the valve installed in the line coming from the intake manifold, and it is a simple vacuum actuated on off valve. I feel like I am air locking the cooling system, what am I doing wrong?

 

[mrkamback]

Hey guys I'm new to this site. I'm having a problem with my vents working. I recently bought a 86' El Camino from an idiot who put a engine in it without hooking up the computer or the vent lines. I know the computer doesn't need to be hooked up (just for emissions) but, it has a Dart intake on it and a Edelbrock carb on it. He unhooked the original A/C (which I still have the compressor) but it's just not hooked up yet. Anyhow my problem is he cut the two hard plastic vacuum lines that go into the car on the passenger side and never hooked them back up and I'm not sure where to hook them up too. I think the one gets hooked up to a vacuum switch that screws into the intake which isn't there right now. There are two different color lines and I think one goes from the carb into a vacuum ball mounted on the A/C Evaporator and then to the other hard plastic line. Nobody can help me (except the one guy who wants me to buy a factory service manual for $180.00) Yea That Will Happen !! Like I said these hard plastic vacuum lines run down under the A/C Evaporator are hard and two different colors anyone who could tell me where they go and where they hook too and even send me good pictures or a real clear picture of them I would greatly appreciate it. Thanks, C.J. My e-mail is [email protected] Thanks Again For Any Help!!!!!!!!!!!!!!!!!

 

[red5776]

Black line goes to constant vacuum. Brown line goes to heater valve

 

[smoke' em II]

have been trying to determine how my heater bypass control valve should be installed. To eliminate the valve in the intake manifold, I am using the heater control valve for a 70 Chevelle, mounting it on the inner fender well, up close to the passenger side hood hinge.

1970 Heater control valve mounting location.:thumbsup:

You should not get any vapor lock in your cooling system if the heater control valve is open, allowing the coolant to flow thru the heater core.

 

[Ed.Camino]

I have a 71 Chevelle with factory AC. I am in the process of putting the entire system back together, and have been trying to determine how my heater bypass control valve should be installed. To eliminate the valve in the intake manifold, I am using the heater control valve for a 70 Chevelle, mounting it on the inner fender well, up close to the passenger side hood hinge. I have checked out the vacuum line to make sure it works.
Now that the valve is installed, when I start the car up, the temperature will climb to well over 200 degrees, and as soon as I put the control setting inside the car to heat, AC, Max, etc. the coolant temp drops right down to 180 or less(running digital gauges), but I of course have hot water in my heater core, which is what I am trying to eliminate.
I have the valve installed in the line coming from the intake manifold, and it is a simple vacuum actuated on off valve. I feel like I am air locking the cooling system, what am I doing wrong?

It could be mounted too high, but I really dont see that as your problem.
Did you install the valve and gauges at the same time or was it not overheating before the control valve install?
Where is the temp sending unit, in the head or the intake manifold?
Is the upper radiator hose getting hot? (this would indicate coolant flow when the T-stat opens)
Have you run it with the radiator cap removed to see if coolant flows? Some coolant will flow out till it gets up to temp, but you should see it drop and flow thru the tubes when the temp gauge matches whatever T-stat ya got in there

 

[Fun 71]

Thanks for the replies, first, the engine temp usually ran 175-180 on normal days before I installed the control valve. On a hot summer day, the car was pretty warm inside without any AC, and as I read about getting the AC system back on line, I realized the heater control valve was needed to keep hot coolant out of the heater core, or that is what I assume it does. The thing that has me baffleled here, is , if I leave my setting on heat, or anything but "off" the coolant circulates and the engine temp stays normal. It is when I have it "off" and start the car up, it acts just like a stuck thermostat, going well over 200 degrees, until I switch to heat, and down she comes to 175?
I appreciate the photo, I have the same valve, it the approximate same location, just a bit closer to the AC box. I have not checked the upper hose, I will do that this afternoon, I am just finishing up a rear sway bar install.

Fun 71

 

[TD509EFI]

Not running the stock bypass hose from the intake manifold to the pump without using a drilled thermostat, will result in the problem you describe. Without either one, coolant doesn't properly circulate through the engine. Depending where you have your temp sensor for your gauge located you will see higher than normal temperature before the thermostat will open.
Having the water valve closed blocks one of the other routes that allows proper coolant circulation in the engine.

John

 

[Ed.Camino]

Not running the stock bypass hose from the intake manifold to the pump without using a drilled thermostat, will result in the problem you describe. Without either one, coolant doesn't properly circulate through the engine. Depending where you have your temp sensor for your gauge located you will see higher than normal temperature before the thermostat will open.
Having the water valve closed blocks one of the other routes that allows proper coolant circulation in the engine.

John

True.
I dont know why, but I figured a small block in stock configuration.
So, what engine ?

With the controls set to heat, the valve will open allowing hot coolant to flow thru the heater core. With the heater fan on, the engine might run cooler but it aint enough to properly cool an engine by itself.

In AC mode, (or, I think, other than heat mode) dampers in the heater box should actuate to redirect airflow so it does not pass over the heater core. (A control valve, if present, should remain closed). If the dampers are not operating that might explain it being hot inside the car.
But that all seems a seperate problem from the engine running hot.

The primary coolant system, (radiator, hoses , etc.) should regulate engine temp regardless of flow or no flow thru the heater core.

I suspect you already know this, sorry if it seems so basic.

If you ran a heater hose from where the heater circuit comes out of the engine to where the circuit returns to the engine, that is bypass the heater altogether, what happens ? ( I know the hoses are different sizes but if you hold your tongue right, it'll work)

 

[Fun 71]

I thought about the stock bypass hose from the manifold to the water pump, but I don't know where it mounts? I am running a small block stroker, with an Edelbrock Performer intake, and that theory of creating a bypass makes complete sense.

As for the idea of hooking the hose together, I actually planned to try that just to see what would happen, which I am sure will correct the problem, but it doesn't help me when I get the AC going. I believe my damper doors are working, but I better re-investigate that possibility. I did rebuild my box when I replaced the heater fan motor.
Thanks again, and give me an idea of where to put a bypass hose for the water pump, or as you said, I could do the drilled thermostat.

 

[TD509EFI]

Fun 71,

My apologies about the bypass hose. I assumed you had a big block. Small blocks don't have that bypass between the pump and the intake because the bypass is built into the block and water pump.

I do know that GM dropped the coolant cut-off valve in later applications such as Camaro's. Without the valve, the heater core still gets hot coolant, though you can bypass the core with the temp door to regulate heat output. If the temp door is working fine ( you can hear it hit the stops when you move it rapidly between open /closed) I would think the problem would point to your thermostat, even if it's new, there's been enough stories hear on TC about defective ones.

The way you have the vacuum controlled heater valve installed should work just fine, and shouldn't cause the problem you've described when running a small block.

John

 

[Fun 71]

Thanks John, so I better check that door to make sure it works, but I am still puzzled. I just went for a drive, and I left the heater and cool/hot off. I hit the end of the street and was at 200 plus. I realize now that when I move the control valve from cool to anywhere towards hot, it must trigger the bypass valve, and lets the system ciruculate, because within 5 seconds, the temp dropped down towards 180. I could try a new thermostat, but non of this was going on until I put the bypass control valve in.
I may just do something to create my own manual bypass, but I hate to clutter up the motor compartment.

 

[PKH66]

I ran into the same problem when I installed a high flow pump. You have to have some sort of bypass in your heater line. Some mopar heater control valves bleed back to equalize pressure to allow the thermostat to open.

 

[Ed.Camino]

You just shouldnt be having this problem due to installation of a heater control valve, (which sounds like it is operating correctly)
I'm thinking possibly a coolant flow blockage or restriction in the heads or intake, but it seems your problem would be worse if that was the case. But it might explain your heater core being so hot.
Are you getting flow thru the radiator with the valve closed ?
Are you sure the intake manifold gasket was open where the coolant leaves the heads and enters the manifold ?
Is your temp gauge sender in the head or at the T Stat housing ?
Put the T Stat in a pot of water with a thermometer, heat it up on the stove and see when it opens. Try it a few times. (women dont react well to dashboard parts in the dishwasher, but a T Stat on the stove will be OK)
While you got the T Stat out, try to stick a wire or something thru the manifold passage and see if you can tell it's open into the head.

 

[Ed.Camino]

Any update?

 

[david bull]

My 71 camino sb,completely original,has the hc control valve on the intake.When I purchased this car it had no vacuum hose on the valve.After much searching I found that the only time it has vacuum is when the controls are set to max otherwise it is open.Although it probably doesn't matter since the blend door is supposed to cut off the hc air flow,I run manifold vacuum to it in the summer which stops the water flow but in no way does it affect engine temperature.DBULL