Dehumidified Defrost needed?

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208Dart

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Hey all, I’m in the middle of my drivetrain build. 6.4gen3 hemi/A833/HDK K member…etc on a 1970 Swinger.

Previous previous owner did a heater core delete and smoother over the heater core section of the firewall and core is gone. I’ll be modifying my dash panel anyways but looking at my HVAC system options.

Would really like to run a coldmaster universal heat/cool setup. But they have no defrost option. I know that some other companies have a dehumidified defrost option… car will be a fair weather only driver but it will be a driver/road trip car. It’s not beyond the possibility of having frost in the windshield some random morning somewhere….. or even a bad humid rain (god forbid) storm will need some air on the windshield to reduce condensation.

The vintage air and classic air both have dehumidified defrost options…. The coldmaster does not.

I’m thinking about either finding a cable or electronic duct valve to tie in the duct work to the defrost vents when I need heat/defrost with the coldmaster system. I’m just unsure on if the lack of dehumidified heat will make it a pointless endeavor?

Does anyone have any advice? Sorry for the long winded post! Thanks in advance.

Mike
 
Is Lewiston all that humid? Up in the "N end" we have days of rain, slushy snow, etc, of high humidity, were if not dehumidified, you at least need outside ventilation. We got by most of my life without. I don't know when the first was I had, perhaps my 97 Olds Cutlass? Nothing before that had it. Nothing in the 70's that I know of.

If the AC system is not designed for this function at the outset, you are wasting your time and may damage the AC. Operating a universal AC in cold weather without that feature in mind is a recipe for liquid slugging the compressor.
 
Check with the larger aftermarket AC suppliers and tell them what you are doing, as well as your average weather conditions to see what they recommend. I know that here in south Texas, AC is almost a must have accessory because of the humidity.
 
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Is Lewiston all that humid? Up in the "N end" we have days of rain, slushy snow, etc, of high humidity, were if not dehumidified, you at least need outside ventilation. We got by most of my life without. I don't know when the first was I had, perhaps my 97 Olds Cutlass? Nothing before that had it. Nothing in the 70's that I know of.

Lewiston isn’t bad but my place is on top of the grade and the car will be driven all over the northwest.
Good to know it hasn’t always been a mainstay feature! I will do some more research.

Check with the larger aftermarket AC suppliers and tell them what you are doing, as well as your average weather conditions to see what they recommend. I know that here in south Texas, AC is almost a must have accessory because of the humidity.

Oh yeah we hit 100-110* often in the summer, I’m not worried about those days, it’s those cool spring/fall mornings that are 35* that we may have issues with.

If I can find a bypass valve or diverted valve to redirect my heat function to the defrost vents I’ll likely attempt to run that first with the coldmaster setup. Can’t find anything so far but likely looking with the wrong search terms.

Mike
 
Dehumidified defrost I think is more of a "luxury" allowing you to defrost the windshield without needing to turn up the air temperature (although more of a necessity in warmer humid climates like where @Demonracer is). The process of heating air in itself lowers the relative humidity, that's why the air inside your home gets dry in winter when it's cold outside. Otherwise like mentioned it would be impossible for defrost/defog to work on vehicles without A/C.

If it's below about 45-50 degrees outside you'll probably be wanting to use the heater anyway.
 
Dehumidified defrost I think is more of a "luxury" allowing you to defrost the windshield without needing to turn up the air temperature (although more of a necessity in warmer humid climates like where @Demonracer is). The process of heating air in itself lowers the relative humidity, that's why the air inside your home gets dry in winter when it's cold outside. Otherwise like mentioned it would be impossible for defrost/defog to work on vehicles without A/C.

If it's below about 45-50 degrees outside you'll probably be wanting to use the heater anyway.

You make a great point thank you.

I’m on the hunt for a control valve to manually/switch controlled divert airflow to defrost vents. If anyone has a lead please let me know. “HVAC Diverter valves” or “Defrost valve” is turning up nothing applicable on google or eBay.

Mike
 
Do a little hot rodding and make a diverter inside.


2 holes, a piece of 18 gage steel, a piece of 1/4 inch rod, a few bends, a few one way washers and your in business.
Screenshot_20230202-140020.png
 
Do a little hot rodding and make a diverter inside.


2 holes, a piece of 18 gage steel, a piece of 1/4 inch rod, a few bends, a few one way washers and your in business.
View attachment 1716043219
That gives me an idea…. What if I found a 2” throttle body and adapted it like you’re talking about? Either find one that’s a 12V drive by wire and switch it, or run a separate cable operation for a classic throttle body?

Mike
 
Go to a pick your part and start digging. You can probably find all kinds of actuators.

I think a throttle body is a bit overkill
 
Go to a pick your part and start digging. You can probably find all kinds of actuators.

I think a throttle body is a bit overkill
It may be overkill but when I look at the few hours I’d spend at a salvage yard inside the dash of some junker I’d gladly pay the extra money to have a part delivered to my door. Time is pretty valuable and scarce for me at the moment unfortunately!

Mike
 
What about an electric exhaust cutout? Pricey but effective: Already designed to divert from one outlet to another, available in multiple tube diameters, and flip-of-a-switch ease.
Don't want to spend that much? Mr. Gasket #5424 is a manual one, but it limits you to 2" diameter tubing. Apparently JC Rip-me isn't selling their $20 versions of the Mr. G unit anymore (at least not that I could find).
 
What about an electric exhaust cutout? Pricey but effective: Already designed to divert from one outlet to another, available in multiple tube diameters, and flip-of-a-switch ease.
Don't want to spend that much? Mr. Gasket #5424 is a manual one, but it limits you to 2" diameter tubing. Apparently JC Rip-me isn't selling their $20 versions of the Mr. G unit anymore (at least not that I could find).

Now that’s a good idea!
What about one of these? Or two of these with a switched vacuum solenoid? Would open one/close the other…

4446AAA4-F290-48BA-9AE4-D4C53525B2AD.png
 
There's always "Studebaker defrosters." I only know of them, because, friend of mine (who still has since the 70's) his WWII MB Jeep, added a Stude defrost unit to it. Simple, square box main heater, and the separate Stude unit Has a coiled/ finned copper tube exchanger mounted on the intake of a small blower motor You just used "T's" in the main heater lines and teed this in

Stude3.jpg


Stude2.jpg


Stude1.jpg
 
On an unrelated note, and I don't remember why "Stude," but you could back in the days of "real Jeepers" --you could adapt a Stude 3 speed overdrive unit to the rear of a Jeep transfer case. With the old WWII an 50's Jeeps which were SO lo geared (some with 5.38's) the Stude OD would give you RWD only overdrive for highway travel. "Rancho" overdrive
T-90-D-18-and-B-W-overdrive.jpg


Garry, the jeep, and son in 70's. This was likely at Mose Lake WA sand dunes. Before the cage was built. Likely had a 327 in at this time. The "later" rendition last I know had a GM V6. He had a 350 in it at some point
_nc_ohc=nK72DUuG82oAX8jmfbc&_nc_ht=scontent-sea1-1.jpg


More recent times and countless rebuilds Notice the small headlights. This is not a civilian Jeep. The headlights are same size as our Mopar "quad" lamps. Note original blackout lamp, shovel and axe mounts. Amber turn signals are just simple old truck clearance lamps
461016_125615734239587_1869548865_o.jpg
 
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Now that’s a good idea!
What about one of these? Or two of these with a switched vacuum solenoid? Would open one/close the other…

View attachment 1716043478
I saw those while looking. My only hesitation or concern was that you'd need two of them, as opposed to the ones built into an existing Y-pipe. On the flip side, the price seems right.

I wondered aloud (to the dog--I'm not crazy) how well that vacuum diaphragm would withstand exhaust heat. She seemed uninterested. Coolant-level temperatures shouldn't be a concern a'tall, though.
 
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