Rob's wrote:

Given that you tested on 2 heat sources I would suspect the cooling unit. I would still bench test on electric before changing the cooling unit.

Cooling Unit Diagnosis
The cooling unit, or coils, of an ammonia absorption refrigerator is the heart of the refrigerator--it does the actual cooling. Everything else on the refrigerator either supports the cooling unit, or is an accessory. No matter how simple or complicated the controls of the refrigerator are, all cooling units require the same three things to operate:

The unit has to be level
The unit has to have adequate ventilation
The unit has to have CORRECT heat

If the three above requirements are provided to the cooling unit, it should work and should work well. If it doesn't work well, then it is a bad cooling unit. It's really that simple. (Also, failure to meet the three requirements above when the refrigerator is in operation can cause permanent damage to the cooling unit.) Of course, don't overlook mitigating circumstances such as a main door that seals very poorly, which would cause a good cooling unit to look bad because of warm air continuously entering the box.

Also, if the cooling unit seems to work poorly only during warm weather, it's possible that one of the requirements above is in a border line state. In other words, the venting, for example, may be adequate for mild weather, but not adequate for warm weather. A cooling unit could also be border line, but it would be prudent to look elsewhere first.

Testing the cooling unit
First of all, if the cooling unit cools properly on one heat source (i.e. gas or electric) and not the other, then the cooling unit, with only a few exceptions, is good and the problem lies in the heat source that is not functioning properly.

Secondly, there are obvious signs of a bad cooling unit.

If you smell ammonia in or around the refrigerator, and you haven't recently used ammonia for cleaning, the cooling unit is bad. No further testing is necessary.
If sodium chromate is present on the outside of the cooling unit, the cooling unit is bad. Sodium chromate is a yellowish-greenish powder in solution inside the cooling unit. If sodium chromate is outside the cooling unit, the cooling unit has a hole in it.
If you hear a relatively loud gurgling or percolating sound when the refrigerator is in operation (being heated), it is a sign of a bad cooling unit. The key words here are "relatively loud". A good cooling unit percolates when in operation, and if you get close enough and listen carefully enough, you can hear it percolate. However, if you hear noise a few feet away, it is a sign that the cooling unit has lost pressure and is bad.
Testing the cooling unit is simply insuring that the three necessary requirements for the operation of a cooling unit (level, ventilation, correct heat) are met. Do whatever it takes to meet these requirements. If you suspect a venting problem, pull the refrigerator and set it on the floor. In fact, pulling the refrigerator and setting it on a level floor meets two of the requirements and leaves only one, correct heat, to worry about. Always test the refrigerator on the electric heat source, unless you are unable to because you have a gas only refrigerator. The reason for testing on the electric side is if the electric heat element gets hot, you can be better than 95% sure that you have correct heat, whereas even a poor gas flame will produce heat. To insure that the heat element is getting hot, you can touch the insulation pack (a rectangular or round sheet metal container filled with insulation located directly above the propane burner) to see if it is warm after about a half hour of operation. CAUTION: touch the pack lightly at first; it is possible under certain conditions for the pack to get super hot and burn you. If the insulation pack does not get warm, you have an electrical problem that needs to be corrected before continuing. If an electrical problem is not the electric heat element itself and/or you want to insure that some other electrical component (such as a thermostat) is not interrupting the heat element, you can hot wire the heat element for better testing conditions. The only weak link in this testing procedure is the less than 5% of the time that a working heat element is not producing the correct heat.

After you have provided the cooling unit with its three requirements, allow plenty of time for the cooling unit to function. You should see signs of cooling in the freezer after about two hours. Allow six to eight hours, or even over night, for an empty refrigerator to come down to temperature. The ammonia absorption style of refrigeration is slower than the compressor style in terms of initially bringing the refrigerator down to temperature. However, once the desired temperature is reached, there should be no problem in maintaining that temperature.

If you have done everything in this section up to this point and the cooling unit does not work or does not work well, the cooling unit is bad and will need to be rebuilt or replaced.