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RV Refrigeration Basics, by Bruce Bernhart

By popular request, here is a handy reference guide by Bruce Bernhart on refrigeration operation for the most popular models of Norcold refrigerators: Operating sequence for the 900 and 9100 Series:

Auto Mode

When AUTO mode is selected, the operating control automatically selects the energy source using the following priority scheme:

When 120 volt AC is available, the refrigerator will operate on AC electric. If 120 volt AC is not available, the refrigerator will switch to and operate in LP Gas mode. On 3-Way models, when neither 120 volt AC nor LP gas are available, the refrigerator will switch to DC electric. DC electric operation is not as efficient as LP Gas or AC electric operation. DC electric should not be used to initially cool refrigerator; it should be used only when other modes are unavailable (for example; while in transit). If no input source (i.e 120 VAC, 12 VDC, or LP Gas) is available, the refrigerator will cease operation.

During operation in AUTO mode, when a higher priority energy source becomes available, the operating controls will cease using the current energy source and will switch to the higher priority energy source. For example, if AC electric becomes available while refrigerator is operating in AUTO LP GAS mode, the refrigerator will switch to AUTO AC operation. If AC power becomes available and is found to be non functional or out of tolerance, the control will revert to the lower-priority source.

Manual Mode

To operate in MANUAL mode, press and hold MODE button until word AUTO (900 Series) or the AUTO LED (9100
Series) disappears and desired operating mode is displayed. If energy source is interrupted while operating in MANUAL mode, the corresponding fault indicator will appear, and refrigerator will cease operation until an alternate energy source is selected or the problem is corrected.

AUTO and MANUAL Modes - Gas Operation Only

If gas does not ignite within 30 seconds, which may occur on initial start-up, the refrigerator’s gas valve will automatically close and the operating controls will select an alternate energy source ( AUTO Mode) or, MANUAL mode, will revert to a stand-by mode in which a fault indicator will appear. The fault indicator will remain until operating controls are turned OFF and then ON again. If gas does not ignite after several attempts, refer to "Diagnostic" and "Trouble Shooting" sections for corrective actions. A different mode of operation may be selected by pressing and holding MODE button. The refrigerator will not switch to new operating mode until the MODE button is released.

LP GAS Mode Operation

When operating in LP Gas mode, the control opens the gas valve and sends a spark to the burner to ignite flame. The ignition cycle is carried out as follows.
1. The gas valve is opened and spark output is activated for 1 second.
2. The spark output is de-activated and flame sense circuit is monitored. If there is no flame 1 second later,
spark output is re-activated.
3. Steps 1 and 2 are repeated until 30 seconds have elapsed, or until a flame is sensed during Step 2.
If burner fails to ignite, the control will turn off gas valve, lock out LP GAS mode, and display appropriate fault code. With

3-Way models operating in AUTO LP GAS mode, the control will automatically switch to DC Electric (heater) mode.

While operating in DC Electric mode, the appropriate fault indicator will be displayed. If DC voltage is available to refrigerator but is below specification, the appropriate fault indicator will be displayed.
If the flame goes out, the control attempts to re-ignite flame, beginning with a new 30 second ignition trial. There is no limit to the number of times flame can be lost and re-ignited.
If the control is displaying a fault indicator, pressing MODE button will disable the indicator and re-initiate 30 second trial for ignition. During 30 the second time interval, an alternate mode of operation can be selected by pressing the MODE button. When control measures input voltage below 10.5 VDC, gas operation is locked out.

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