Dometic NDA1402 - Defrosting; Real Time Clock; Automatic Defrosting

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SECTION 10

DEFROSTING

10.1 Real Time Clock

To get the best performance from the refrigerator, defrost-

ing is performed when the least amount of demand is on

the refrigerator. Therefore the refrigerator has a real time

clock that controls the defrosting process. The clock runs

even if the refrigerator is switched “OFF”. However, if the

12 volt DC supply (battery voltage) is disconnected, the

clock will continue to run only about three weeks. So if

the battery voltage has been disconnected for more than

three weeks, the clock must be set again. This will be indi-

cated by horizontal bars (- - - -) in all four, seven-segment

displays. Even if this “clock not set” warning is not shown,

the clock should be checked at regular intervals (at least

once per year) to ascertain that the time setting is correct.

It is also recommended to reset the clock when entering

different time zones. (Refer to section 1, page 11 for set-

ting of the clock).

10.2 Automatic Defrosting

Defrosting is initiated automatically every 24 hours, at 1:00

AM ( based on clock setting). However, a defrosting may

be skipped if the air temperature in the freezer is greater

than 18° F, or the DC voltage is less than 10.5 volts.

There is a blocking function that inhibits automatic de-

frosting during the rst 24 hours after the refrigerator is

switched “ON”. This 24 hour blocking function is reinitial-

ized every time the refrigerator is switched “OFF” for more

than one hour.

Temperature “pull down”

When a defrosting is initiated, the rst thing that hap-

pens is that the refrigerator pulls down the compart-

ment temperatures to thermostat “cut out” levels. If

these levels are not reached within one hour, the de-

frosting sequence starts anyway.

Cooling unit relax time

After the temperature pull down period, the real de-

frosting sequence is started. The cooling unit is now

switched “OFF”, but nothing more happens for 10

minutes to let the cooling unit relax.

Heating in the freezer

After the relaxing period, the heating elements in the

freezer and in the water drain are switched “ON”. The

fan in the freezer is at the same time stopped to pre-

vent the food from being heated by hot air.

The heating stops when the temperature on the cool-

ing surfaces has reached 41° F or when 75 minutes

has elapsed. If the heating is stopped by the time cri-

teria, the defrosting is treated as incomplete. An in-

complete defrosting could depend on either extreme

ice on the cooling surface, or that the battery voltage

has became so low that the heating effect was insuf-

cient.

If 2 incomplete defrostings occur in a row, the warn-

ing message “Er 01” is displayed on the front display

panel.

Note: The WARNING “Er 01” on the front display

panel indicates that 2 or more consecutive defrosting

attempts failed. This message will disappear when a

defrosting has completed successfully. But it will also

be cleared if the power is switched “OFF” and then

“ON”.

The heating is also stopped before the defrosting is

completed if the battery voltage drops below the bat-

tery protection level (less than 8.5 volts DC).

Heating in the fridge

After the defrosting of the fresh food side, normal

thermostatic operation is restarted again. However,

the heating element in the water drain line is still “ON”

for some time. It is switched “OFF” 30 minutes after

the start of the fresh food defrosting period.

After the defrosting of the freezer, the cooling unit

is restarted again. It takes some time before cold is

produced and during that period, the defrosting in

the fridge now takes place. After a one minute delay,

the heating element in the fridge is switched “ON”.

The fan in the fridge is stopped during this defrost-

ing cycle. The heating element in the water drain line

remains “ON”.

NOTE: An automatic defrost may also be skipped if the

control module detects a fault with either the heater or

the thermistor for the cooling surface in the freezer sec-

tion. These conditions will be indicated by an error code

displayed on the front display panel. See section 11 for

trouble shooting error codes.

The start of an automatic defrosting may be delayed for

up to 3 hours based on two criteria. If the battery voltage

is lower than 10.5 volts DC, or no cooling source (Gas

or Electric) is available. If these two conditions are met,

the defrost will be started and will complete as normal. If

these two conditions are not met within 3 Hours, the de-

frost for this 24 Hour period will be skipped, and recorded

as incomplete.

The heating stops when the temperature on the cool-

ing surfaces has reached 41° F or when 20 minutes