Marvel UL-40 Refrigerator

Renovated Marvel model UL-40

One thing I relearned from renovating the 1948 Boles Aero was that the more planning you do, the faster it'll be completed. Of course I know this well since my professional life was all about planning and executing complex projects, but at home I tend to "wing it" more often than not.

In any case I knew that one thing you really need to decide up front is the layout of the trailer interior including what appliances you'll be using. The more you know about specifics such as size, weight, power, etc. will only be beneficial.

I've decided to try to keep the interior of the Clipper looking close to original. This is not going to be a "restoration", rather I think of it like rebuilding it taking advantage of what we have available today. Ideally the non-aficionado will think it's original but it will have modern conveniences.

I decided to keep the kitchen layout original. My Clipper was gutted by a prior owner, but I do have the disassembled cabinets to go by. The layout of Clippers seems to have varied over time and even the owners (and their respective state departments of motor vehicles) are unsure of the model year they actually own, so I've relied on the cabinet pieces and other indicators (e.g. stove vent fan opening location) to determine the layout. From this I scoured the internet for a picture that is close to hat I think it would be originally.

My inspiration for the kitchen area - found online

The image I found shows a Marvel refrigerator to the left of the entry on curbside and a Coleman 3-burner stove on streetside. This configuration matches the physical evidence from Decatur so that's the layout I'm pursuing.

I have a Coleman 3-burner stove that I salvaged from my '48 Boles Aero. But I didn't have a Marvel refrigerator so I searched and eventually found one near to me on eBay marketplace.

I've seen pictures of Marvel refrigerators with this same outer box configuration for many years with the only obvious external difference being a left or right opening door. The insides do seem to vary a bit with some having a closed freezer section and others having a U-shaped evaporator tray. The ones with the U-shaped evaporator also included a drip pan arrangement so that you could use them as an icebox. I'm guessing they all used the same 120V R12 refrigerant compressor mechanicals.

For my purposes I wanted to convert the compressor mechanicals to 12VDC so that it could run primarily on batteries. I'd also done some research and decided I'd replace the fiberglass insulation to increase the R-value. Along the way I planned to refinish the exterior as well.

A more detailed look at the fridge made it obvious I had some work ahead: there was more than surface rust that needed to be addressed. And as I tore down the fridge it made complete sense: the fridge is basically a box within a box. Condensation is going to build inside the inner box and freeze while condensation is also going to build inside the lining between the inner and outer box. This latter condensation is going to be trapped and pool at the bottom of the outer box and lead to rust.

The bottom panel of the outer box was about 50% rusted out. To add insult to injury a mouse had found the holes and decided the space between the inner and outer box would make a comfy home!

House of Mouse

I'll try to summarize the steps I went through to tear the fridge down:

If you plan to replace the compressor, find someone who will recover (ie suck out) the R12 refrigerant before you start. This could be difficult as there aren't a lot of people that deal with R12 anymore. Try vintage appliance groups or possibly automotive shops that do more than routine maintenance.

If you plan to continue using the compressor leave it intact and reinstall it later. You should replace the wiring as it's likely old and frayed, plus it doesn't have a ground run. It's a really simple circuit: power for the compressor and fan are routed through the thermostat. Power to the interior light is tied into the power input line that runs to the thermostat.

Remove the door. The hinges have a polished cover that can be easily pried off with a screwdriver.

Remove the (crumbling) plastic on the inside covering the gap between the front fascia pieces and the rear mainbody of the fridge. This will expose a bunch of small (rusted) nails fastening the front fascia to a sturdy wood frame that provides structure at the front of the fridge. Surprisingly, the entire inner box is also cantilevered off this wood frame (it is not supported otherwise).

Remove the shelves from the interior of the fridge. Note that the evaporator (the U-shaped metal finished shelf with tubes attached) will not come out till later.

Remove the nails fastening the fascia pieces and then remove the fascia pieces. The nails aren't easy to remove and I found two varieties - simple wire nails and "twist" type panel nails that are much harder to remove. Note that the side fascia must be removed before the center top fascia can be removed. You'll also need to remove the thermostat knob and faceplate. Be careful with this last as hopefully they can be cleaned up and reused.

Vampliers - I love them

At this point you can remove the entire refrigeration mechanical unit together intact. Remove the screws securing the compressor to the bottom of the fridge frame. Remove the bolts suspending the evaporator from inside the top of the fridge. There might also be some pliable caulking filling a gap in the wood frame, remove this. You'll also need to either disconnect the momentary switch that controls the light inside the fridge or cut the wires. Once you do all this you can carefully slide the entire compressor/evaporator mechanism out of the fridge as a single intact unit.

High pressure capillary tube, suction tube and thermostat capillary run up the side

Remove pliable caulking used to fill gaps

You may need to clip the wires from the fridge light momentary door switch

Refrigeration mechanicals removed intact

Next remove the large number of nails holding the wood frame to the mainbody of the fridge. It's very similar to removing the fascia a few steps back. You can leave the frame screwed together or you can unscrew it and take it out piece by piece. I'm not sure there's an advantage either way.

At this point the inner fridge box should slide out freely.

Disassemble the door by separating the inner and outer halves. There are a bunch of screws located under the door gasket, simply unscrew them.

Screws holding the door together hidden under the gasket

Two door halves opened up

So by now teardown of the fridge is complete. 

Next up was refinishing. First I removed the paint and rust using a variety of techniques. this was truly the hardest and most time consuming step. I sandblasted, ground and used paint remover to get the old paint and rust off.  I planned to use POR-15 on all the nonvisible surfaces so I didn't need to remove all the rust from those (POR-15 encapsulates rust - I really like it but some people hate it).

I also did some minor body work - removing some dents in the door. I thought I'd done an excellent job until the glossy finish got on the door and then I realized bodywork is an art and I'm not skilled in it. I missed a small dent or two and some of the sections looked smoother than others.

Bodywork on door

Another benefit of using POR-15 is that it helped me solve the severe rust problem on the bottom of the outer box. That section is not structural (remember the inner box is cantilevered off the front wood frame - no weight rests on the rusted out bottom outer panel) so I really just needed to seal it up. POR-15 can be combined with fiberglass for a very hard and sturdy repair. I applied POR-15 and then imbedded a layer of fiberglass cloth to both the top and bottom sides of the rusted out panel. The result is rock solid, maybe stronger than the original sheet metal.

POR-15 and fiberglass repair of bottom side

POR-15 and fiberglass repair of inside of outer fridge box

After the POR-15 application had thoroughly cured, I sprayed on primer and white appliance epoxy for all the visible surfaces using my Fuji Semipro 2-stage HVLP. I can't say I was impressed with how this went but it's done. I normally spray wood finishes and this was my first time spraying metal with epoxy.

Door and cover panel with fresh appliance epoxy finish

Next I needed to reinsulate before I could start reassembly. You can go a lot of different ways here but I wanted to maximize the insulation so I chose to use 2lb closed cell foam. It's relatively light, basically waterproof, has an R-value of about 6.5 per inch of thickness (vs 3 for fiberglass), and provides structural rigidity. If I poured it rather than use the standard rigid boards then I would also get the benefit of filling the entire void with insulation. It comes in a 2-part form that you mix and then pour into the space you want to fill. It expands about 24:1 from it's liquid volume. But it takes planning, multiple pours, and trimming when (not if) you get too much poured. Oh and if it gets on a surface you don't want it on it's never going away. 

A much easier approach would have been to wrap the outside of the inner box with 2" foam board and filled the door with some other easy to use product.

So I came up with some Rube Goldberg ways to pour the foam. And it worked but took a lot of effort that I'm not sure will yield results commensurate with the time spent.

Pour through the holes and let excess bubble out - note the new evaporator plate and new fridge light socket installed before foam was poured

Pouring 1/2 of the door and then sandwich together

After insulating the various sections I was able to rebuild the fridge box. As mentioned there was some trimming of the foam required to get everything to fit. That's a good thing as you want as few voids in the insulation as possible. (I used an oscillating tool to do the trimming and it worked spectacularly.)

When rebuilding the door I replaced the old gasket. This was definitely not cheap ($7/foot at AntiqueAppliances.com) but necessary. Something to watch out for on the door reassembly is getting the hinges oriented correctly. The hinges are not vertically symmetric; you can't flip them 180 degrees without creating problems. They should angle in slightly toward the inner box; it's very subtle. If they aren't both oriented correctly you'll have problems getting the door to seal properly. I learned the hard way.

New gasket for the door

As I mentioned much earlier, I wanted to convert to a 12VDC system so that it can run off of batteries since I intend to primarily camp at the national parks and forests. There are easy ways to do this and harder ways. The easier way is to purchase a icebox conversion kit that are commonly used on sailboats. I've swapped messages with several people that have gone this route with their Marvel fridges and they all had good things to say.

A notable icebox conversion kit others have used with the Marvel is the Nova Kool LT201-RT6. I really can't speak to it since I didn't use it but if I had gone the kit route it's what I would have used.

By now you may appreciate that I'm not smart enough to take the easy approach. In truth I love to learn and try new things so I did some research and decided to cobble my own system together from components I'd source separately. This took a lot of time researching and more sourcing the parts.

In the end I used a Secop BD-35F compressor (model 101Z0212), a Secop AC/DC electronics control unit (model 101N0510), a condenser I sourced via AliExpress, and a evaporator plate I sourced via AliExpress. The latter two parts took weeks for delivery and I wasn't sure what I'd end up receiving but they were extremely cheap and they seemed to be exactly what US distributors were selling repackaged. I also sourced some bits and pieces via Amazon, such as the very important filter-drier and some of the copper fittings.

I watched a bunch of YouTube videos on compressor replacements, etc and also studied images of commercial icebox conversion kits. Additionally I used the Secop heat load calculator and capillary selector app to verify my component choices would work. Both apps are available on the Secop website but the latter wasn't particularly helpful for a couple reasons. First, the "CalSel" app seems to provide the length of capillary tubing for optimal cooling which is extremely long, much longer than any commercial design I saw online. Second, you're really sort of stuck with the capillary tube included with whatever evaporator plate you use - these are usually integral to the part.

In any case, I laid out a design and built it up using the components I'd purchased on the plate that the original refrigeration equipment had been mounted to. I was able to find someone that could use the fan but the compressor and condenser are sitting in my garage awaiting the next ruthless purge. 

Original Refrigeration Unit on Left, new Secop compressor and condensor on right

Plumbing and layout of the new Secop-based refrigeration unit - Note I installed access ports on the high and low side

The Secop electronics unit provides a couple nice features that you can take advantage of but are in many/most cases optional. It provides for: a simple LED diagnostic readout of errors if they occur; adjustable compressor speed so you can ramp up the cooling; and selectable battery low voltage protection. I chose to implement the first two.

The electronics unit will flash a simple 12V LED if it encounters errors. I bought a standard 12V LED on Amazon for less than $5.

And the compressor speed can be adjusted based on the resistance in the thermostat electrical loop. They provide a few discrete resistance settings in the electronic control datasheet, but I confirmed with Secop (via email) that the resistance curve and resulting compressor speed are continuous. So I found a cheap ($10) 10-turn 2K ohm potentiometer on Amazon (Taiss 3590S-2-202L 2k Potentiometer 10-Turn Rotary Wire Wound Precision Potentiometer) and wired it in. The potentiometer increases resistance as you turn the dial for 0 ohms to 2K ohms - basically the same range as Secop lists on their datasheet. The potentiometer has a dial so you can repeat the settings pretty accurately and so I used a multimeter to determine the setting that corresponded to the compressor speeds listed in the Secop datasheet (not really required but nice to know).

[I'll note that you can buy a speed controller from Frigoboat that provides fixed resistance increments for about $50. They also have a "smart" controller, the "Merlin II", for about $150 that modulates the compressor speed based on a pre-programmed sequence. And finally Isotherm offers an "Intelligent Temperature Control" that provides a thermostat function, compressor control and LED error readout all in one.] 

I mounted the LED and potentiometer on a small metal tab toward the front of the compressor plate. You'll be able to see it easily when you remove the front fridge access plate. Ideally you'll never need to see it or adjust anything, but it's there if you need it.

Front of refrigeration section with LED error indicator and compressor speed adjustment on the left side

Note that I did install a 12V 140mm 1500 RPM computer-type fan on the condenser that is controlled by the electronics unit. To my ear it's the loudest part of the install and the manufacturer claims its only 26 dBA (seems more in the 35-40 range to my untrained ear).

Refrigeration unit ready to install in fridge (dangling wire goes to thermostat)

With 20/20 hindsight I would have done some preliminary electrical testing using 12V power before I installed the unit in the fridge. I did have some wiring issues that were easily resolved, but after install you're crouching down looking into the bottom of a fridge with a flashlight vs having the thing sitting on a bench.

I mounted the refrigeration section in the Marvel and soldered up the capillary and suction lines. This was difficult because there is limited space to wield a large torch under the fridge and solder doesn't flow in all directions equally and you are sort of constrained in which way the fridge is oriented. But I got it done...sort of.

I borrowed a vacuum pump and manifold from a local auto parts store to draw a vacuum and it seemed to be working fine. I let it sit overnight to check for leaks and in the morning all was looking good so hooked up the refrigerant, connected the 12V power supply and started adding refrigerant. I added about 4oz which is what others online said would be about right. I started the compressor and all seemed good ... but I didn't hear the characteristic gurgling of the refrigerant traveling to the evaporator plate. 👎

Drawing a vacuum

So the troubleshooting ensued. Fixing commenced, and trouble shooting of the fixes was needed, and more fixing. Lots of cursing and frustration edited out.

I'll generalize by saying the capillary tube is really small and can get plugged with solder easily. It doesn't help when there really aren't good fitting connections between the filter-drier and the capillary tube (basically you have to crimp the filter-drier to fit). Solder can block the capillary tube and fixing it can lead to leaks because the connection isn't optimal to soak up liquid solder. It can be a frustrating circle.

Eventually I got it all sorted out and the Marvel started making pleasing gurgling noises and getting cold. Not exactly the same gurgling noise as pouring that first glass of wine from a bottle, but just as satisfying.

Once I felt the fridge was working I replaced the interior trim that closes the gap between the front fascia and the inner box. The original had some plastic trim but it had crumbled to dust and isn't available anymore. Some T-molding might work but I decided to try "Magic Peel & Stick Caulk" that I found at Home Depot.

Gap between front fascia and inner cold box

Gap with caulking strip applied

The caulk strip looks good and hopefully it'll work well. If not then I'll try some white T-molding.

A side note on this gap: the gap also runs around the outside of the fridge. Right now I'm going to leave it as is (ie uncovered). When I install the fridge that gap will be hidden.

Oh and the last thing: I decided the wire shelves needed to be replaced. They were in sorry shape and with the change to the evaporator plate one of them just didn't fit anymore. So I've ordered custom-made replacements. Not cheap, but it'll complete the look.

So would I do it over?

It was way more work than I anticipated. If I knew then what I know now I'd probably search real hard for a unit in better initial condition and then I'd use an icebox conversion kit instead of rolling my own. I did learn a lot and have the satisfaction of doing something few others have done.

At this point I've buttoned the Marvel up and stored it off to the side in the garage so I can get to work on other things that need doing.