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Want my 1956 Imperial to be a freezer in the summer

Posted: Sun Jul 26, 2020 6:16 pm
by BIGGUNDOCTOR
First post here.

I have a project that I want to do, and I am doing the research to make it happen.

I have a 1956 4dr Imperial that I am putting onto a 1994 Dodge 2500 4x4 chassis with a 12V Cummins to use for some offroading. I live a bit outside of Fabulous Las Vegas NV where it gets very hot during the summer - it was 122F recently. In my other cars I have measured interior temps of 168F and dash temps of 225F+ when the sunscreen was not up. So not only is the air hot, but everything else is too, and takes quite a bit to cool it all down. My 98 Saturn wagon struggled during the summer. The Craptastic 07 Nissan Versa was blowing 34F at the vent after I serviced it when I first bought it. I believe it is the first car I have had here where I could back the fan down from maximum. The usual AC setting here is on maximum for 6 months. Unfortunately, the AC was the only thing that was good on that car.....don't buy a first gen Versa, dead at 128k. Both the Saturn and Nissan are 134a systems, so I know it will get cold enough as long as the system is set up right. As it was explained to me the Saturn struggled because it was 134a in a system sized for R12. GM did not know how well they would sell when first launched, so minimal effort was put into the HVAC system. The later ION AC is excellent.

So, with the 56 Imperial I will have a huge internal volume to cool, much larger than the single cab donor truck. The car has the optional factory Chrysler Airtemp AC evap in the trunk, and I am thinking about incorporating it into the new system. This is going to be a build, so I plan on running some new vents where I want them; feet and seats for starters. I hate being cool in front and still sweating against the seat. Has anyone done a dual compressor set up? Run both for rapid cool down, then cut one once it is cooled. So, instead of twin turbos, twin AC. It would also offer some redundancy if one goes, there is a backup. How well will the trunk evap work with 134a? Obviously I am also looking to put some high volume fans in as well to keep the extra vents pushing cold air. Another peeve of mine is when I switch to both feet and face the air volume drops a lot. From what I have read the standard car AC is anywhere from 3 to 7 ton capacity, and I want a lot more. Is it doable, or should I just install a ThermoKing reefer unit on the roof? :lol:

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Mon Jul 27, 2020 2:34 am
by Al9
BIGGUNDOCTOR wrote:From what I have read the standard car AC is anywhere from 3 to 7 ton capacity


Well it's actually lower than that since most auto expansion valves are rated around 1.5 to 2 ton. 3 to 7 is more like a shuttle bus/city bus.

The dual AC compressor setup is optimal for a dual evaporator setup since it favors oil return, a huge issue when the system is running with one evaporator live yet with a dead blower fan (and dedicated solenoid valves are an additional maintenance issue). Want to turn rear AC off? The compressor clutch disengages and that's it, it's no longer a live evaporator that can pool oil and refrigerant inside like there's no tomorrow unless you keep a minimum fan speed or have some other fancy device that keeps the evaporator warm so that the TXV doesn't basically hunt between a snap shut and nearly shut condition (or needs to be forced to stay open partway creating other issues).

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Mon Jul 27, 2020 8:50 am
by BIGGUNDOCTOR
I checked several sources and they were all in the 5 to 7 range, and one said a bus would be in the 20+ range. The explanation was the car needed to be so large due to the interior temps hitting 120F-160F and not wanting to wait forever to have it cool down. I nicknamed my 98 Saturn SW2 the rolling Easy Bake oven. With the amount of glass it had the solar input was incredible. Here during the summer you keep the AC on while parking, putting the sunshade in the windshield, and getting ready because as soon as you turn it off the heat gets unbearable, and I mean instantly. It goes off, as you are opening the door to exit.

I am looking to do some other custom touches like window shades I can close, as I am not a big fan of tinting. Yes, tinting works, but makes night driving a chore. A front to back divider behind the seat to cut the cab volume down as well. Thought of that with the Saturn.

The split system is kind of what I had in mind. One compressor for each separate system, as opposed to the system in my ambulance with one compressor and two evaps. I know the basics of automotive AC, but still have a lot to learn. The Cummins has plenty of torque to spin two compressors, unlike the Saturn which would drag down when the AC was turned on, It got 40 mpg in the winter and 35 with the AC on.

Any good resources for sizing components (evap, compressor, blower fans) for the application?

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Mon Jul 27, 2020 10:05 pm
by bohica2xo
Compressor capacity on automotive compressors is generally someplace below 4 tons. A Sanden 7H15 is able to make 2.13 tons at maximum capacity. The GM V7 compressor makes it to 3.98 tons capacity maximum.

Running two compressors with separate systems will work. The larger TM31 compressors used on ambulance & fire trucks only makes 4.83 tons, and is not a cheap unit. FYI the OEM compressor for that 1994 Dodge is an SD7H15. If you can fabricate mounts there are lots of compressor choices.

Your best bet is to leave the solid firewall of the imperial, and ignore the modern pickup A/C parts. As Ice will point out, all of the OEM systems drag in outside air - even when set on recirculate. The old 12,000 btu (1 ton) knee knocker in my dad's 1954 Cadillac Fleetwood did a great job - because it recirculated 100%

Insulation is key. I did my share of conversion vans between 1977 - 1985. Spray foam insulation on the walls & roof before the interior install was a night & day difference. Something less combustible is recommended for the floor & firewall. Seal everything up. Outside air leaks bring in heat & exhaust leaks.

Tint & sunshades are a poor substitute for covering the glass on the outside of the vehicle. Sunlight goes through the glass and heats the tint film or shades.

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Tue Jul 28, 2020 2:15 am
by Al9
bohica2xo wrote:all of the OEM systems drag in outside air - even when set on recirculate.

Seems to be true - the recirculation flap on my car features a small bypass hatch that seems to let something through from the interior even when set to 100% fresh air. Wonder if it also works the opposite way.

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Tue Jul 28, 2020 8:21 pm
by BIGGUNDOCTOR
Mounts are not a problem. I am a machinist by trade and ran a machine and fab shop in my 20's.

Re: Want my 1956 Imperial to be a freezer in the summer

Posted: Tue Jul 28, 2020 8:44 pm
by bohica2xo
Hopefully you still have a Bridgeport within reach.

There are plenty of compressors out there to choose from. Pay attention to the drive ratio for the diesel. The average compressor can spin to 6,000 rpm, some are ok at 7500 on the rev limiter. Under driving the compressor from an engine that spends it's time below 2500 rpm can leave some capacity on the table.

What kind of shape is the rear evaporator assembly in?