What is the purpose of this? Costs of running of ammonia refer on 120V vs compressor?
2.7A is on the lower side for ammonia heaters, and 2.9 is on the higher side for residentials, new models can draw 1-2A. Different duty cycle, different shape (RV fridge shallow front to back, cold air spills out when you open the door), different coolant.
The bottom line is - 120V ammonia heater is less efficient in KW/year than 120V compressor fridge.
Ammonia fridge in LP mode is a different story because then you have to count mostly propane cost, while the thermostat DC draw is low, under 100KW a year.