Hey Guys. With warmer weather getting close, I want to reduce the temperature in the Vettes. interior. Thinking about putting cut-off valves on the heater hoses but don't want to cause the heater core to start rusting etc.(thinking that water circulation will prevent it). What do y'all think about adding cut-off valves and not close them off completely for the summer. This might allow some water to go through the core and hopefully keep it from rusting or going bad. Any better ideas out there? I know, the interiors of these cars is a sweat box anyway, but just trying to find a better mouse trap. Oh yeah, the AC don't work, yet! Thanks

 

There's no gain whatsoever by plugging the heater hoses as long as the blend door seal is in decent shape. And as heater cores are made from brass they won't rust anyway. Once you get your A/C working again you'll want to reduce the amount of cooling on summer evenings by adding a bit of heater core heat to the colder air. So I vote for leaving the hoses alone.

 

Auto or manual transmission ? Headers installed ?

There is no real good way to prevent heat inside these cars unless you are willing to insulate.

But things that can help and are factory features.

1. Air vents make sure they are closing properly. Measure the vent temp vs outside air. This is a good test to make sure the vents are closed properly.

2. Does you car still have the foam collar around the transmission bell housing. This prevented engine heat circulating around the transmission tunnel.

3. Is the exhaust routed in the factory locations. If you have headers are they ceramic coated.?

4. Does this engine run at the normal operating tempatures ?

5. Is the transmission running at the normal tempatures. If an auto check fluid level and color for transmission heating.

6. If an auto is the transmission cooling lines routed to the radiator still in place.

7. Are the front air rams / spoilers still in place to route cooler air to the radiator and into the engine bay ?

 

My 78 has a valve on the heater hose that is vacuume activated this was stock I believe on these cars. When the controller is set to AC the valve gets vacuume and cuts off the hot water supply to the heater core. If this valve is not closing the interior does get pretty toasty but if it works the interior really does not get that much hotter than ambient temp ( windows down in the sun of course). Mine was not hooked up to the vacuume line, when I hooked it back up the difference was incredible.

 

Fix the vacuum shut off. If yours is like mine the controls need work. If thats the case two brass ball valves will cool u down till the hvac is working to spec.

 

I forgot about this. This should be on the top of my list of factory features.

 

Cago's list is a great starting point to ensure systems are working as intended. But as you have surmised, as other posters, the large rear window, an underpowered A/C system and inadequate floor insulation makes for a difficult set of factors to overcome.

The best book on the topic, is Air Conditioning Strategies for the 63-82 Corvette written by Michael J. Davis, published in 1997. It's out of print and others have reported difficult to find.

A few years back in a trip to St Louis from Myrtle Beach, I tracked cabin temp changes with A/C on. I tracked cool air as it came through the vent and then general cabin, watching as the gap increased throughout the day. Even with the A/C working perfectly, blowing cold air at 41 - 44 degrees, the green house effect of the large window overwhelms the systems capability to blow and maintain cabin temp. Cabin temps rose from a comfortable 80 degrees to over 90 by mid day.

Best option...drive at night!

 

Applying Tint to that big rear window helps block the sun out.. If you still have a functioning factory shut off valve, you don t need a manual valve. Unless, like me, your cam is too big to produce enough vacuum to close it.. It which case a manual shut-off is the best option.. it will not hurt your core, as its filled with antifreeze which resists corrosion ... If you ever get A/C working, swapping the Blower wheel for a C4 wheel will increase output by about 30-40%

 

The hot water shut-off works a bit differently than others stated.

When the "Cold-Hot" lever is moved all the way to "Cold" a cable operated lever* operates a simple on-off vacuum switch which applies vacuum to the hot water shut-off valve**.

*the hot water shut-off switch is behind the glove box near the lower-left.

**the hot water shut-off valve is installed in-line in a heater hose on the right (passenger) side of the engine.

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If the hot water shut-off is not working you will ROAST! I know that from personal experience! Once I got that working my stock '79 interior is comfortable. Again, the hot water is stopped ONLY by moving the temperature lever all the way to "Cold"--it has nothing to do with "A/C" or "MAX A/C" selector settings.

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If perchance you decide to use a manual shut-off valve you only need one (on either the supply or return heater hose) to COMPLETELY stop flow through the heater core. Those who say you need two valves may be good mechanics but they have no comprehension of hydraulics.

 

This has been talked about before .you can do a search and find a lot a ideas.i put in one shut off valve .That helped with a lot of the heat but you also need to check for holes in the fire wall.With someone riding with you have them feel for heat .

 

I've done: 7004r Tranny, VBP rear spring, Bilstein shocks, Wilwood brakes,, Dewits radiator & electric fans. But best mod so far (beside 383) has been decreasing my interior temp. It took insulation and most of the above mods mention but I've got a cool ride. Its well worth the time and expense.

 

What about physics?...Convection- Convective heat transfer?

The water in the heater core WILL become 180º - if you do not have two valves- just takes a little longer.

 

I am in the process of putting some insulating material inside the t tops. Also inside the doors themselves.Also, there is a clear timt that will supposedly knock down the UV from coming into the car and heating it up. I don't have any experience with it and I can't remember the name but I think a few searches should turn it up. SO the dark tint will take care of the back window and this stuff was designed for the front windows. And make sure the cowl vents are sealed up. They could let some hot SC air in to get mixed with the A/C.

 

If that were the case, GM would have used TWO vacuum operated shut-off valves, not one.. My A/C is 40* coming out of the vent and with the larger C4 blower wheel will blow your hair around on Max High ... My car is black and Temps reach 112* here in July/August.. I m nice and cool

 

one valve has worked for me for 20 years . put one in and see if it works .if it does not, put in another one .I replaced the seal in the door at your right by your feet .I also pluged up several holes in the fire wall.i all so added some heat wrap around the outside case of the air conditioner.the headers are real close to that box.seal all the air ducts in the car. lots of air loss there.

 

Here are a few sample temp readings: Ambient air was 80*F/entire cabin has been insulated with reflective heat/soundproof HVAC blanket..........

Steering Box by Exhaust manifold 160* F

Steering column at Firewall 130* F

Steering column inside car by gas pedal 110* F

Steering column at dash mount 98* F

Steering column at steering wheel nut 90* F

Exhaust pipes under footboard 300* F

*Footboard inside the car 95* F (Entire interior of car is insulated/soundproofed with economy-grade Foil-backed heavy-duty bubble wrap)

Exhaust Pipes under the floorboard 250* F

*Floorboard interior 95* F


The steering column transfers a good amount of heat.










Before insulation was added the heat coming from the firewall and floorboard was nearly unbearable.

 

I studied most of the threads here on reducing cabin heat on these cars. My car has been down for a few months for repairs. In the mean time I installed the heater shut off valves in the heater hoses. I also installed Dynamat Xtreme and Dynaliner to the floorboards. It gets over 100 degrees here many days during our summers. I can't wait to see the payoff of these modifications.

 

If you have no water FLOW thru the heater core, very little heat will ever get conducted through the [non-flowing] water and to the core.

One shut-off valve in EITHER line will do the job.

And, if you install a shut-off valve in one of the heater hoses and you STILL have excessive heat coming into the passenger area....your problem is NOT coming from the heater core.

 

Street, the dynamat will help with noise but is not designed with blocking heat in mind. It will to some degree due to it's additional mass that is added to the floor pans but the heat will still soak through.
I found refletix to be effective at combating the heat soak. I have fat mat mega mat on my floorboards for noise then the refletix on top of that with 3m spray adhesive, then the stock jute and carpet on top of that. works very well for staving off the heat.
That with the c4 fan added and electric cooling fans (condensor cooling) makes my cabin as cool as I want, even on 100* days.

You might be surprised.
I had only one valve initially and the core still got hot and radiated heat on the passenger side. Fine for the driver, but the passenger was feeling it. Second valve and now no more heat.
All the sources of heat are cumulative. Each one that can be eliminated adds to the comfort of the temperature in the cabin and if equipped with a/c reduces the work load on that system. Which will in turn keep your coolant temps down keeping your engine running cooler making it more efficient, staving off detonation, allowing more timing or less octane etc,etc.

 

I have "Dynaliner" installed over the Dynamat Xtreme. This should help with the heat issue. I need to correct my post.