Honestly speaking, I don't have enough idea on how to convert normal outlet refrigerator to portable or outdoor. If you are talking for the watts or volts. I think you need to have a compressor before you do it. Good luck!

 

You're all forgetting a very basic problem - auto air conditioners ran off R-12 (older) or R-134A Freon.

Refrigerators (until just recently) run off R-22 Freon.

Neither are compatible in vapor pressures or the required lubricant.

You could conceivably run the evaporator coil in a refrigerator with automotive freon but you'd need to change the expansion orifice and possibly other items. All the seals would have to be replaced, system flushed and the proper Freon & Lubricant introduced.

A very large inverter may be your only choice and they don't take too well to the starting current required by compressors.

 

To the OP,

Firstly, the ambient temperatures would have a large impact on your choice of cooling. A fridge is only able to cool to a certain degree, so if you have a fridge that is designed to have a Δt of 30°C that would mean that in ambient of 40°C that the inside of your fridge would be at 10°C. You also do not mention what you want to cool, is it a couple of cans of pop?

Compressor fridges are by far the most efficient and there recovery time are much faster, by that I mean the ability to return the fridge back to its set temperature.

Absorption fridges, the ones commonly used in RV's etc. are much less efficient and are controlled by a heat source. So you would have a dual 12 / 120V element as well as a gas burner. A typical 180l fridge would require 180W to heat the ammonia solution that does the cooling. The cooling circuit for these fridges is critical and the more cool air you have passing of the cooling fins, the lower the temperature. Absorption fridges are often fitted with thermostats comprising a capilliary tube that controls a diaphram, these are notoriously innacurate and can lead to freezing in warm climates (you gave to turn the control all the way down in the day to achieve cooling which at night then causes the stuff at the bottom to freeze.

Peltier devices, these are very nice but genreally are not suited to warmer climates as they battle to get down to the required temperatures.

What you require is 3 - 5°C in the crisper and -18 to -15°C in the freezer compartment.

I would think that you are best off buying a Gas / 12v / 120V RV type unit. A word of advice though, the unit must be level to better than 5° so you would need to make a levelling frame. Avoid overpacking the fridge as it will not deliver the desired result. Don't stand at the fridge with the door open while deciding what you want, get in an out, remember I said their ability to recover temperature is poor. Make sure there is plenty of air circulating around the cooling fins at the rear of the fridge and beware it get warm. If the thermostat is the capilliary type then run the fridge on gas for best temperature stability. DONT travel on gas but on 12V.

I have camped for the last 15 years with a stand alone absorption chest freezer, a seperate absorption fridge / freezer combo and a Coleman peltier cooler. The Coleman is used exclusively for excessive salad stuff and the likes that just needs to be kept fresh. This is transfered into the fridge as space allows, once transferred the Coleman takes no further part in the camp. These I use in Africa where temperatures will often be in the 40°C's.

Good luck

 

Large Peltier coolers have come down substantially in price. It would take me forever to find but I bought several from a guy on eBay that eventually figured out I was a potential volume customer. Turned into an e-mail conversation and he had access to a direct import source thus quoted me some rather impressive pricing in volume.

I have a love/hate relationship with these things due to getting rid of the heat they generate on the hot side. I was only using one per device thus still heat sinks, however if you needed to run several a simple recirculating water system might be in order.