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So researching A/C thermostat options, I started thinking of a two-stage thermostat. So hear me out here and tell me if you think this would work:

Use a preset thermostat (Part #119-9920 on this pagenostalgicac.com/controls-motors/ac-thermostats.html) back in the truck to prevent the unit from freezing up.

The use a second thermostat in series with it up under dash to regulate actual cabin temp. So basically if either of those thermostat hits their temp setting threshold it cycles the compressor off.

Work? No Work?

Also found some picture of the unit mounted in a trunk here. I dont see any straps or brackets. I wonder if it mounts to the floor through the bottom panel. This wouldn't exactly work on a Packard as that area of the trunk is not flat as it is in the studebaker.

studebaker-info.org/tech/aircon/Novi/Novi.html

more pics:

markiiforum.com/showthread.php?t=1106

Evap mounting is probably going to need some brackets -- maybe similar to those they are using for the MarkIV. There is a decent photo of those in that 55 MkIV install manual in the lit section.

Thermostat concept is good but I'd wonder with the rear AC if there will be enough free air circulating up in the dash area to reliably work the second thermostat. If the sensing tip is under dash, I think not -- so capillary placement will be important. Since the capillaries are designed for insertion into the evaporator coil, there may also be a bias applied to the thermostat for the differential between contact with metal and free air.

The Hurricane rear unit from Old Air I'm using on the 47 has a rotary adjustable thermostat at the rear. Theory is set it once and forget it. Am not convinced that is the best so currently I'm thinking about a different solution. One I have been toying with if I decide to change would be to mount Nostalgia's cable operated unit 119-9925 at the rear and operate via a long cable. I used a 12' premade shifter/throttle cable for my rear vent control. The particular cable I chose was not the best choice since it is heavier and has straight rods with threaded ends and a lot of unneeded travel. Overkill and hard to mount for a thermostat (or vent) so been checking into other options.

Just for illustration, here is what I wound up with for the 47. As mentioned, cable is big so haven't totally decided to keep the vent cable setup as is. If I go with the thermostat cable as well, the cooling switch will probably be changed to Vintages combo unit and the speed/temp function will share the left bracket and a smaller vent cable stays on right.

The typical universal choke cable is too short as is Vintage's combo fan switch/cable. After working with that first premade cable, I think I've found a source for regular raw bowden cable in 5 meter lengths. Been a low priority so haven't pursued it yet. If I go that way, making a control end or figuring a way to add length to a premade cable assy should not be difficult. Made something on the lathe for the first cable so if you would be interested in that single cable approach and a push/pull control something like the original panel, I could move the priority and pursue it farther for both of us.

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Thats pretty slick work Howard. I may pursue that with you.

But, i'm wondering if a preset one in the trunk is all I need to keep the evaporator from freezing up and perhaps control the temp in the cabin with the dual blowers. HIGH - HIGH, LOW- HIGH (or HIGH-LOW), LOW - LOW, LOW - OFF (OR OFF - LOW).

Technically the blowers could be on without the A/C on for circulation, and wire up the circuit so the A/C wont come on unless at least on the blowers is, and replace the center switch in the "Novi" style console with a simple On/Off switch to control the A/C operation.

So basically one of the blowers has to be on for the A/C to be on, but the blowers can run without the A/C on.

A 12v BOSCH style relay and a few diodes would make that an easy circuit to build.

Also I found another Packard control panel picture from a 57:

Reviewing the Mark IV A/C Manual, it appears to control the cabin temp via the blower speed. One rheostat for each blower, and a central ON-OFF switch for the system. So similar to my idea, just the Novi unit has two-speed blower motors.

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V8 Packards had fixed evap temp and controlled the temp out by varying blower speed. Those had a single blower & was not the most comfortable for the entire car. It was a trade off -- for the front to be comfortable, back seat passengers would be hot unless it was on high. For the back seat to be comfortable, the front needed parkas. A trunk unit is just the opposite but at least with two blowers you will have a better chance of finding a common point with the fixed temp.

The original prewar Packard trunk was fixed temp. The postwar Packards & Cads, ARA, the Novi and some of the higher end MarkIV units -- actually most mfg's trunk units -- had two blowers but varied the temp by gas bypass or an early form of suction throttling. Mechanical units that were controlled by the pull out knob or a lever under the control panel. Packard & Cads Frigidaire unit by a rheostat controlled heater fooling a thermostat to open or close a solenoid valve.

Another idea for a thermostat that struck me if to use a bimetallic thermostat with a rotatory adjuster (like used on old house thermostats). That could be used below dash for cabin temp in conjunction with a preset thermostat in the condenser to prevent freeze up.

Or a small circuit with a thermistor and potentiometer to regulate the temp. Basically whether it be mechanical (bimetallic) or electronic, just something that can be set to a target temp and cycles a circuit on above that temp, or off before that temp. That is really how a standard house thermostat works.

Just pondering here.....

I really think this could work....a very simple bimetallic, adjustable temp thermostat which is already in the normal operating range:

broan.com/products/product/72f0238b-dbba-49c5-831b-f7087b90a691

For something only around $10, definitely worth a try.