Refrigerators
The subject of refrigerators for the GMC is a well-traveled one. There are two basic options: absorption refrigerators, which depend on a heat source, usually propane, to initiate a liquid/gas cycle using ammonia in a spiral tube, and compression refrigerators, which use a compressor to sustain a vapor compression cycle. Typically, an absorption apparatus is considerably larger than a comparable-capacity compression system, and in an equivalently-sized compartment, that space has to come from somewhere, and that somewhere is the refrigerator box. Absorption refrigerators have less usable capacity than compression refrigerators.
| Absorption | 12v Compressor | 120v AC with inverter | |
|---|---|---|---|
| efficiency | most efficient on propane heat source | most efficient with modern Danfoss (or knockoff) compressors | Can be fairly efficient while compressor is running; inverter use involves some continual phantom power loss. |
| energy source | some ("three way" or "two way") have an option for a resistive electric heat source. 120 volt only practical for | 12 volts, less than 10 amps | dedicated or whole-house inverter running off 12 volt house |
| expense | approximately equivalent to 3-way RV refrigerator pricing | cheapest by far, but electrically inefficient, with waste power from inverter even when compressor is off. | |
| safety | potential fire hazard; many RV fires are reported to start in refrigerator compartment | 120 volt can shock if | |
| use restriction | not legal in many states to run on propane while underway; will not work at any tilt above 3-5 degrees. | no restrictions; most can operate at extreme angles, certainly any that might be encountered on a mountain road | no restrictions; most can operate at extreme angles, certainly any that might be encountered on a mountain road |
| modes | Propane or 120 volt, usually switchable at front panel. 12 volt not typically used. | Always 12 volt, running or stopped | When connected to shore power, should be powered directly by 120 volt AC source. |
There are those who swear by their propane-fueled absorption refrigerators, and there are those who swear at them. In the best of cases, an absorption refrigerator takes the better part of a day to get to temperature, and once there it takes a while to recover if the door is opened. There is a reason we don't use absorption refrigerators in the home ... they're just not competitive with compressor-cycle fridges in any area of performance, and they are a potential fire hazard. Even moreso in a moving RV. They compromise the overall heating and cooling of the RV because they must vent to open air. In short, because the efficient 12 volt compressor refrigerator has come of age, and high-capacity LifePo4 batteries are readily available, along with affordable solar, there are few reasons left to choose an absorption fridge.
12-volt Refrigerators
Several 12-volt refrigerators are recommended by the GMC community. None fit the existing space in a standard GMC-built interior better than the Norcold N8DC, though. This model has been observed to pull a maximum of 5 amps while the compressor is in operation. Once cool, in a comfortable interior and with the old absorption air vents sealed, the N8DC can be expected to cycle about 1/4 to 1/3 of the time, consuming at most 40 amp hours per day. Vitrifrigo also makes a competitive model.
Wiring
The existing 12-volt circuit running to the refrigerator compartment of a GMC is 12 awg wire, capable of sustaining 10 amps over a 16-foot run. A Norcold N8DC pulls considerably less than that; for peace of mind, this circuit can be fused at 10 amps without issue. If you're going the route of running a dedicated inverter to power a 120 volt compressor fridge, you may find that your compartment is already supplied with a 120 volt AC circuit; a larger inverter can supply that circuit, or you can run dedicated 10 gauge 12 volt wiring to the refrigerator compartment; 25 amps can power a 300-watt inverter, providing enough power to run an apartment-size refrigerator such as the models from RCA or Frigidaire.
Sources
If you're open to scratch and dent refrigerators that may require cosmetic repair, National RV Refrigeration in Shipsewana, Indiana has a solid reputation in the GMC community.
