scorpion18z

Is it more efficient to place the manual cut-off valve on a particular heater hose (ie: hose from water pump to heater core, return from heater core through A/C vacuum heater control valve to intake manifold). Does it matter? I know this may raise the question as to why do this, but living in Florida it has been suggested that stopping the water flow to the heater core by this means is more efficient than relying on the vacuum heater control. When winter arrives I would just turn the flow back on again. I also realize that I will not be able to "adjust" the outflow temperature with the manual cut-off valve, but when using the A/C it is always on maximum setting for temperature and just using fan settings for adjustments. One thing that I have been thinking is when driving without the A/C on I will eliminate the residual warm air flow because of the constant water flow through the heater coil. Input is welcome. Pictures appreciated.

langg

What I did is install a (stock) vacuum operated shut off valve in the line from the pump to the heater core. I then used one of the small vacuum valves for the headlights, mounted the one for the heater beside the one for the headlights (below the steering column). I now can positively shut off the water to the heater without messing with the original hvac controls.

Langg

7T1vette

It really doesn't matter which hose you choose for the shut off valve. I would look for a place where a section of heater hose runs against the inner fender area and is easily accessible. Just cut through that hose, install valve and clamps and attach it securly to some solid surface (so it doesn't 'flap in the breeze').

I installed mine in the pressure side of the heater. But, once you dead-head the system, that isn't a big deal, either. I just made sure that it didn't look that obvious [painted the valve semi-flat black like the inner fender] and easy to reach without getting near the fan or belts.

scorpion18z

Excellent! Thanks for the suggestion. It already feels like a meat locker with the conversion over to 134...I didn't expect it to be so effecient, but it is. Cost was only $100 and I did not need to do add or convert any of the original parts. Did clean out the orifice which hadn't been done in 30 years, vacuumed it down and re-charged with the 135 (feeder valves may have been changed). Anyway, I was just trying to stop the heat radiating from the vents when driving around town with nothing turned on. I will keep an eye for changes in water temp readings, but so far, none indicated...August and September in Florida are coming though.

Al77Vette

Why choose. I used an AC Delco 15-5533 from local auto parts store. Connected both hoses and a vacuum line back to dash controls.

scorpion18z

I can't make out the hook-up with this part. I am seeing 4 connections points with two hoses????

Al77Vette

Here is a link to the part. Look at the first 4 pictures.
https://www.google.com/search?q=AC+D...w=1313&bih=596

John 65

Thats what I did on my 77. It dont jump out at you. Put a vac operated Raycor valve on my 68 but went with this on my 77. Painted the clamps black too.

MIKE80

Not much vacuum coming from my engine, so I installed brass ball valves on both lines. Also, if the heater core area gets a leak I can cut off that part of the system.

U17

"Search" is your friend... Lot's of threads concerning shut off valves.. Some say it's already there on A/C cars ...

Arkyvette

An 82 has a good valve already. Just run its vac line to manifold vac directly. Solved my hot cabin problems for free.

scorpion18z

When you say "dash controls" are you referring to the A/C temp control? When in A/C max positing can the does the temp control level still vary the temperature output by controlling hot water flow through coil or does this flow control valve shut off flow completely?

Paul L

Mine.

Mashman

It's a bypass valve, not a cutoff valve. There are four ports, the valve either sends the flow straight through, or the flow is rerouted thru the middle of the valve. The advantage of this type of valve is that since it doesn't stop the flow, it does not create backpressure the way a cutoff would.

scorpion18z

In conclusion to this topic, after considerable online research and suggestions made by learned and experienced members of this forum, I have decided to stay "stock" and put my trust in the factory vacuum water controlled valve. Nothing against the bypass or cutoff valves, but I want temperature control of my A/C and I occassionally need defrost capability (especially during our hot, humid rainy season down here). I have tested the factory valve and it works just fine. I also tested source vacuum and it is also to specs. If I was to use another system, it seems for logical to use the bypass valve configuration over the cutoff for obvious reasons. Thanks to all of you who have participated in this discussion. It was most appreciated. Sometimes it is just as well to leave things as they were designed. Now I will go looking to fix something else that is not broken (lol).

larrywalk

Although the stock ('78) vacuum heater control valve will stop water flow with a vacuum signal while the engine is running, when the engine is off (such as when you're running an errand to the store), the vacuum goes to zero, opening the valve, and lets convection slowly circulate hot engine coolant into the heater core. When you return a half hour later, the hot coolant has made the cabin even hotter and will take the A/C even longer to cool down. Usage of a manual shutoff valve is best to prevent this hot soak problem.

For the other question, blocking of coolant flow through the heater core will not hurt anything, in fact, for those not wanting heater at all, the hose fittings on the intake manifold and water pump may be removed and replaced with 1/2" NPT pipe plugs.

7vette6

So one valve that just shut off the flow to the heater core would work right?
#1 it would create too much pressure and #2 water would work its way back through the out hose of the heater valve?

Arkyvette

My stock constant vac shutoff valve works just fine. Not enough heat gets through with car off to notice. I imagine heat soak would happen with either style valve. Why would there be any more pressure at the shutoff valve? Its the same pressure as the rest of the cooling system, just no flow.

scorpion18z

I am thinking if you are still going to try this out (stopping water flow through heater coil), then a "manual" by-pass valve would be the ticket. No backflow when engine is off as probably with vacuum controlled by-pass. By the way for all that is interested, I live in FL (not the hottest state in the Union, but hot all the same) and rely soley on my original stock flow vacuum flow valve and have no outstanding issues as long as the car is running causing flow over the condenser coils. I will admit that it is not at maximum cool air while in traffic around town, but I try to avoid that situation as much as possible and head out on the highway looking for adventure (damn that would make a good verse in a song).

chevymans 77

These threads interest me in that every so often someone adds a shutoff valve and causes cooling issues. The bypass valves allow flow from the intake to the pump which is possible that this allows needed flow when the T-Stat closes, it may even prevent the pump from cavitating. The pump has a bypass hole (3/8”) to allow for a small amount of flow but this may not be adequate for the pump without the flow from the heater hose. The small amount of flow from the heater hose does prevent the situation where when the T-Stat closes there will be no water flow in the block and thus could cause hot spots.

This is just me thinking out loud and nothing really to back it up.

If it was me I would stick with or add a bypass valve instead of a block valve.

Neal