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Jul 27, 2012
Reaction score
Brisbane - Australia
My Car
1973 Mustang Convertible
Hi again to all,

In late Feb,2023, i posted a thread to do with the ongoing failure of my Classic Auto Air's heater shut off valve. A quick recap of that post, revealed that my first heater shut off valve malfunctioned shortly after installing the new aircon system back in 2013. I purchased a new part from Classic and got back on track again. Fast forward to the present day and that replacement valve has just broken down again, failing to open and close properly at all.
Since 2013, i would have used the aircon only a handful of times. To buy yet another genuine replacement part from Classic, will now set me back close to $300.00 Au to land it on my door step here in Australia where i live.

That's stupid money on a part that has shown itself to be prone to malfunctioning at any time. If i spent that money now, and bought a replacement, what guarantee would i have of future trouble free performance from the new part? It begs the question of the quality of this part in the first place. I wonder if this part was American manufactured or subbed out to a cheap overseas labor country. If you own a Classic Air system and never had any heater control valve issues, then that's great. In my case, i have been let down poorly and had to pay the price.

In any case, i decided not to buy that part, and came up with a cheap, DIY solution to get me out of jail with this issue. I simply purchased a ball lever valve and installed it online to one of my heater hoses. The idea here is simple in the fact that the new ball valve now shuts off or opens any super hot water going from the intake manifold and into the heater core under the dash. In the warmer Summer months, you can close off the hot water to the heater core, and in Winter time, open the valve to let the hot water enter the heater core and flow back to the water pump inlet. I have left my faulty Classic Air heater valve installed for now. It's stuck in the open position.

Also, just for the record, i'm running a 302 Windsor. The heater hose setup is hot water comes out of the intake manifold and goes to the (lower) heater core input pipe on the firewall. The water then comes out of the (upper) heater core outlet pipe on the firewall, an gets sent to the inlet pipe of the water pump. The Classic Air heater valve is a strictly one way flow valve that is located on the (upper) heater hose located just a short distance from the firewall. The location of that valve, open or closed, means hot water is always allowed to get stored or passed through the heater core at any given engine running time, and so creates unwanted heat to radiate into the cabin. To put it another way, it's like installing a mini version of your main front big grille radiator, and placing it in the cabin. You can imagine the amount of heat that would generate out from the under dash heater core, even though it's fairly enclosed in the heater box body or housing.

I also mentioned in my last post, that a small manual lever valve with an under dash push/pull knob attached to a cable is available to buy at a cheap price. That is another option to consider if you want the added advantage of opening or closing the valve from the cabin.

So this has solved my heater shut off valve problem, and also taken care of another problem in regards letting hot water to (always) enter the heater core and thus, let heat radiate into the cabin all year 'round at any time you are driving. Problem solved there too. Also, because this radiant heat problem was happening, i noticed that it retarded the cooling performance of my aircon in Summer. After doing some recent thermometer testing, i am now getting a 39 Far or 4 deg Cel lower temp improvement. Not too bad. The new valve cost me $32.00 Au or $21.00 US. In my case, i bought two 5/8 inch brass barbed ends separately. These barbed ends can be bought with smaller bsp thread sizes to marry up with a smaller valve body if desired, but in going smaller, you are reducing water flow through the valve. Your call there.

So finally, if anyone is interested in doing something similar to myself here, just a few tips to help out. Firstly, some folk may say that the ball valve i have installed is too big and ugly. Fair comment there. I chose that size because the inner dia bore of the ball valve is close to the inner 5/8 inch (16mm) dia heater hose, thus not restricting any water flow. Second, if you buy a new ball valve, be careful and check out the performance specs of that valve. Make sure that it has a decent and adequate pressure and temperature rating capacity. This is important, as all ball valves have an inner nylon sleeve. This sleeve must have a temp spec to handle super hot water flowing through the valve. In my case i bought a good quality valve, with a temp rating of 170 degrees Cel or 338 degrees Far. I am well covered there. If your point of purchase shop does not provide a temp handling spec, then move on to another supplier that does. If your new ball valve can't handle the high engine water temps, then failure of the valve will certainly follow. Water boils at 100 Cel or 212 Far. I would not buy a valve rated at under the 110 Cel or 230 Far mark. I also bought two new heavy duty hose clamps to ensure a trouble free no leak result, and i used plumbers tape around the threaded ends of the two barbed tails as well.

See my photos below of the new ball valve install. Many thanks,


UPDATE. (Thursday the 8th of March)

I have just been in contact with the Classic Air tech advisor regards more info on the water control valve for the Elite system. He tells me that the water control valve electronically, progressively opens and closes in relation to where you progressively position the hot/cold temp slider control on the dash. This setup means that you have full variable control of how much cooling or heating effect you end up with in the cabin. In other words, the amount of heating of the cabin is governed by the amount of hot water flow moving through the heater core. As well, the instruction manual states that when the mode lever is in dash only or defrost only position, it will act as an over rider, and will guarantee the compressor will kick in no matter what. It also states that when the temp control lever is all the way to the left(full cold), then that also guarantees the compressor to kick in as well. (See my new pic below.) It shows you what's going on with the mode lever adjustments, and when the compressor kicks in on full dash and defrost modes.

That all said, and getting back to my ball valve install, you can understand that with the progressive opening and closing of the Classic Air heater valve, it will be a given that this electro mechanical device is delicate and sophisticated by design, and so, will be prone to playing up or malfunctioning over time.
With my Classic valve stuck in full open position, i can now understand why it was really blowing hot air out, even with the aircon on maximum cold position, and the full dash vent selected, and the compressor running.

So with my ball valve setup, the trick will be to find in winter time, a sweet temp spot, and select a position with the on/off lever, that lets a certain amount of hot water flow into the heater core, that provides a reasonable or comfortable amount of heating effect in the cabin. Opening the ball valve lever in full open will probably let too much super hot water to enter the heater core and out again, and thus, the cabin get too hot too soon. I will experiment with that, and see what results tweaking the lever produces.

It is clear to see that by installing my ball valve, i have lost the ability of variably adjusting the level of heat in the cabin now. That is a negative trade off i will have to live with in using the ball valve setup. Also, with the original healthy Classic Air heater control valve located down stream from the heater core, controlling the amount of hot water flow passing through the core, that now changes with the ball valve located upstream and controlling the amount of hot water flowing into the heater core. Being setup this way now, i am hoping that by controlling the amount of hot water into the heater core, i will still have the ability of regulating how hot the cabin gets by adjusting and selecting the lever position of the ball valve. I will do follow up testing on that score.

I'm still glad i went this way with the ball valve, as it has solved the problem of radiant heat entering the cabin with the heater core taking in super hot water all the time. Regards Tony's feedback, i would say it would pay to do some dash temp and mode control testing and checking out the condition of anyone's Classic heater control valve to see if it's progressively opening and closing properly. Also, since the Classic Air system electrically talks to the heater control valve in a special certain way, i would say that an aftermarket replacement valve will most likely not be compatable with the Classic system. With the chip and recalibration question, it might also pay to do a reset of the calibration setup, as a trouble shoot thing as well. ( not sure about that) My best advice is to contact the tech team at Classic Auto Air if you need any tech advice about your system. They have been very helpful and patient in helping me out with my questions. Believe me, it's been a big learning curve on how their system works. In that regard, i feel that the instruction manual is not detailed or comprehensive enough in explaing the technicalities and features of their system.



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Careful with this particular model. It says not to use with water. I suspect that is due to the viton seal. Viton isn't the best choice for water but is good with fuels and oils. EPDM would be a good choice for our cooling systems.

Edit: I wanted to refresh my recollection on material compatibility. It appears the viton is fine with water and ethylene glycol (antifreeze), it's the high temp aspect, or steam that's the problem with viton. In either case, EPDM is the material of choice for our cooling systems.
Last edited:
Careful with this particular model. It says not to use with water. I suspect that is due to the viton seal. Viton isn't the best choice for water but is good with fuels and oils. EPDM would be a good choice for our cooling systems.

Edit: I wanted to refresh my recollection on material compatibility. It appears the viton is fine with water and ethylene glycol (antifreeze), it's the high temp aspect, or steam that's the problem with viton. In either case, EPDM is the material of choice for our cooling systems.
I am not planning on adding this valve unless I confirm I have leakage, but this valve is rated to 120C. They have a cheaper option with NBR (nitrile) rubber that is rated to only 80C. Both EPDM and Viton will work fine in a cooling system. The advantage of EPDM is that it is much cheaper, but that doesn't mean Viton will not work. Viton has actually better mechanical performance than EPDM at higher temps while the opposite is true at lower temps (<-20C). Viton, being a fluoropolymer, has better chemical resistance than EPDM.
just put valve to hose going to heater core rather than from heater core, eliminating constant heating of core.