7/9 Updated Heater Control Valve

I've been researching this for a while, finally came up with a viable solution for us 'grandpa' series owners. Hopefully this will help a few of you...

The factory heater control valve on the 7/9 series cars is normally closed unless you have the heat on. Normally this wouldn't be an issue, however the way the system is designed and the coolant flow run, when the valve is closed, there is limited, if any coolant flow around the backside of the head. If you have the heater on, coolant can leave the back of the head and return to the water pump by way of the heater core. Given the recent discussions on cooling system issues, plus my lack of a working heater since the last valve broke after just a year, I went searching for a solution.

I came across this little piece of plastic, which so far seems to be a great solution. The cost was $34 from Napa, not sure the application, but the part number is 660-1357, and the local store had it on the shelf. The only thing you'll need to swap the stock valve for this one is 2 extra hose clamps.

NAPA 660-1357 is the front heater valve for 90-95 Chevy Astro Van and GMC Safari Van

Installation goes in place of the factory unit with the 'front' marking getting connected to the hose from the head. The bottom 2 ports get t'd into the return line from the core, which you'll need to remove about 2" from. This valve operates the same as the stock unit, except that it will bypass the core and send coolant back to the pump when vacuum is supplied, rather than simply being closed. When open coolant runs to the core and back via the normal return path.

Initial results also show it allows more coolant to flow thru the core, which in turn means you can bake biscuits easier with the heat from the vents.

And now the pic's (don't have one of it installed, cam was dead).

nice

sweet.
refresh my memory... are the to and from heater lines the same size? I sorta thought one was smaller...

MistrThou said:

sweet.
refresh my memory... are the to and from heater lines the same size? I sorta thought one was smaller...

Click to expand...

The lines are the same size. Something like a 5/8" ID.

gsellstr said:

...however the way the system is designed and the coolant flow run, when the valve is closed, there is limited, if any coolant flow around the backside of the head. If you have the heater on, coolant can leave the back of the head and return to the water pump by way of the heater core

Click to expand...

After the water jackets, the back-side of the head is the 2nd place Coolant from the WP goes to.

What am I missing?

Sure, coolant can go there or is already there in static flow, but how does it leave? The exit from the back of the head is via the heater core, but if you block that, you can't get the coolant to leave the head. That's where the bypass here comes in, allowing it to circulate out of the back of the head one way or the other.

Heater performance last night in 50* weather was greatly improved as well, even with the fan on high. Normally it would give more air but at a cooler temp than on the next speed down. Same temp at any fan setting now.

Also checked head temps between front and back of the head and the back of the head dropped 15-20* compared to the stock heater control valve, and temps were fairly even front to back now.

Thanks for trying this out and providing the initial results!
I'd love to see a sketch of the installation just to make sure I understand correctly (I'm one of those visual types) - I'm about to do a full cooling system replacement, and this looks like a great option.

For the "Tee", do you have the lines going from each of the bottom units into a tee on the core line?

gsellstr said:

Sure, coolant can go there or is already there in static flow, but how does it leave? The exit from the back of the head is via the heater core, but if you block that, you can't get the coolant to leave the head. That's where the bypass here comes in, allowing it to circulate out of the back of the head one way or the other.

Heater performance last night in 50* weather was greatly improved as well, even with the fan on high. Normally it would give more air but at a cooler temp than on the next speed down. Same temp at any fan setting now.

Also checked head temps between front and back of the head and the back of the head dropped 15-20* compared to the stock heater control valve, and temps were fairly even front to back now.

Click to expand...

On my whiteblock, coolant goes: WP -> water jacket -> back-side of head -> front-side of head -> return to WP.

I don't remember my redblock, but it can't be any other way.

Heater line is tapped off the block, and Valve stands on its way -- HV is closed by vacuum until Climate Control Unit reduces vacuum and opens it.

The heater core supply is off the back of the head, goes to the valve, thru the core, then returns via the hardline to the water pump. If memory serves, the pump provides a feed to the head and block, but I don't recall there's any way for it to return if the valve is closed. Even talking with a well respected Volvo guru, he suggested finding a way to do this as well, which is what got me looking for a solution.

Like I said, in my whiteblock coolant travels across the head, from back to front and it returns to the WP via the Pipe manifold. This mainfold (outside the motor) collects all returns -- head, heater core, radiator, oil cooler. The heater core circuit is an "add-on" kinda thing, and it has no bearing on coolant flow inside block and head.

If anything, having the bypass would delay warm-up, even slightly.

I don't know the circuit of redblocks, but I would be shocked if it is otherwise.

It won't delay warmup any more than having the heater turned on, and actually, it'll still warm up faster than with the heater on in a stock setting, since there's no cooling effect of the core. The whiteblock routing is quite a bit different, especially with that manifold across the back, which the redblock's don't have.

I've been trying to locate a coolant flow diagram but haven't found anything that actually applies to the redblock itself, even in the greenbooks...

Yeah, I got a rudimentary Parts Diagram of the B230 and it looks nothing like what I have in my car.

There's some VERY helpful info in this thread regarding coolant flow as well, if ya got time to read it. Thomas has some basic info in there that might help it make sense, along with some of the reasoning for doing this swap.

http://forums.turbobricks.com/showthread.php?t=121189&highlight=coolant+flow

I see it. Like you said, Thomas's concern was for uneven head cooling, when speeds of 4200 rpm or greater are sustained for hours (racing situation), or turbos.

Good thinking Doug. Results prove it.

I think you may be proceeding from an incorrect premise:

gsellstr said:

The factory heater control valve on the 7/9 series cars is normally closed unless you have the heat on.

Click to expand...

I understood that valve was normally open. So coolant always circulates through the heater core, regardless of where you set the temperature slider, *unless* you also selected "Max AC". At that point, vacuum would be routed to that valve, and it would be closed. For all other settings of the HVAC, the water keeps circulating through the core.

A quote taken from the thread you linked:

Yea said:

The only time that vacuum is supplied to the heater control valve (to close valve) on all 700/900 series cars is when the climate unit is set to max AC.

Click to expand...

And from Matt:

Matt Dupuis said:

I know that the heat control in a pre-90 (at least) 700 is managed by an air door that adjusts the mix of cold and warm air, from 0-100%, and I know that this valvey-thingie is not part of the heat controls.

Click to expand...

As I understand it, that valve is normally open, not normally closed.

So, if I understand this properly, the issue that you have solved only arises when you're both driving hard and also running "Max AC".

Interesting mod, but that's a pretty rare circumstance (for my own driving style & local climate, at least) where it would be a real benefit.

edit - your temperature results are really interesting. I wonder if that's because of generally better flow that's possible with this unit, relative to the OEM. Or maybe you were already documenting the test with the Max AC position selected. Or maybe I'm the one who has it backwards.

Not sure on the lore of the heater valve only being closed at MAX AC, as that is not the case. It is closed normally, and the moment you slide the temp control lever slightly off the cold side, the vacuum to the valve is killed, allowing the valve to open and coolant to flow to the core. The temp control is indeed based on an air door setup, but coolant flow is vacuum controlled. This updated valve is normally open with no vacuum, same as the OEM valve. The control head provides vacuum to the valve unless you have the temp slider off the coldest setting.

If the valve were open with the AC running you'd have a hot heater core fighting against a cold evap core, leading to mediocre cooling at best. Also, the only thing the MAX AC setting does is flip the system from outside air to recirc, with the rest of the system behaving the same way.

Not quite sure where some of the comments from that other thread came from honestly. Even the greenbook data goes against the stuff you quoted from that other thread, let alone my findings on my own vehicle.

I actually think my 85's green book does say something like that (the max AC thing) but I don't think it's right or maybe it's only true for the early cars?

So some basics that I think I gleaned; use this valve, GrpA the holes in the head, use a Hepu pump, and for a low/mid hp DD all will be fine, forever. That about right?

Technically the Heater Valve is open -- when car is NOT RUNNING. The moment engine starts, the vacuum pulls the valve closed, which makes it "Normally closed". Climate Control then controls its variable opening by modulating the vacuum. Some cars do it with a cable.

Like I said, when heat is off, this bypass in effect provides a loop -- hence a head cooler. Results show it. I also like the fact that Volvo heater ports are used, i.e. inferring here that volume of coolant diverted to bypass is calculated somehow. This is the "restrictor" Thomas and Matt were talking about in the other thread.

Actually Henry, there is no modulation in this valve. It's either go or no go, with temp being controlled by an air door in the dash. This valve only supplies or prevents flow to the core.

Also, thanks to Alden for digging this up...application data...
Chevrolet Astro 1990, 1991, 1992, 1993, 1994, 1995 FRONT VALVE
GMC Safari 1990 FRONT
GMC Safari 1991, 1992, 1993, 1994, 1995 FRONT VALVE