Ac Sensing; Dc Voltage; Dc Voltage Requirements; Grounds - Dometic NDA1402 Service Manual

3.3 ac Sensing

The incoming 120 volt AC supply is constantly checked
for availability by means of an opto-coupler. There is a
delay of approximately 15 seconds before a change is
recognized to avoid spurious switching. When AC is not
available in AC only refrigerators, the message "no AC" is
shown on the front display panel.
SectIon 4

dc Voltage

4.1 dc Voltage reQuIrementS

Clean Direct Current (DC) power is mandatory for high-
tech circuits to operate as designed. A battery will provide
straight line DC power. The converter and alternator pro-
duce DC power by a series of diodes that rectify alternat-
ing current to DC. The Dometic control system will only
tolerate up to 6 volts AC on the DC line (Also known as
AC ripple). AC ripple can be measured by a digital volt-
meter set on the AC scale and measured at the main DC
terminal block connections at the back of the refrigera-
tor. 6 volts AC or less is acceptable. If AC volts exceed
6 on the incoming DC line, the power source should be
cleaned. AC voltage in excess of 6 volts will affect the
processor and create erratic operation. When testing for
AC ripple on the DC line put a load on the converter. The
operational range of the unit is a minimum of 8.5 volts
DC to a maximum of 18 volts DC (However 10.5 volts DC
minimum is required to activate the defrost system). The
unit will automatically shut down at 18 volts DC or greater,
and come back on when voltage has decreased to the
proper operating range. The refrigerator requires at least
8.5 volts DC for proper cooling operation. The refrigerator
must be connected to the battery circuit with two wires of
adequate capacity to avoid voltage drop. Proper polar-
ity is crucial for refrigerator operation. No other electrical
equipment or lighting should be connected to the refrig-
erator circuit. Just because you can read volts, does not
mean you have the amps to operate the control system.
If relays buzz, lights go dim or out during operation, this
could indicate there is a loose connection somewhere. As
a last test, use a battery and run wires directly to the DC
terminal block. If the unit works OK on direct DC voltage
the problem is in the coach, not the refrigerator control
system.
note:
The defrosting cycle will not start if the voltage is
below 10.5 volts DC. It is important that the wires to the 12
volt DC terminal block are of proper wire size.
•
Check the wire gauge to ensure that it is in accor-
dance with recommended dimensions.
length (ft)
< 33
33-66
> 66
min. size (aWg)
12
10
8

4.2 groundS

The operation of the Dometic refrigerator is also depen-
dent on good, clean ground connections. Loose or corrod-
ed ground terminals create an unknown resistance factor
that can affect the voltage detected by the Power Module.
A loose negative DC wire will create a negative millivolt
signal that the control board will pick up and create erratic
operation. Check the integrity of the grounds from the re-
frigerator all the way to the power source/battery. Clean or
tighten any suspicious looking connections.
Main Terminal Block
note:
The DC terminal block located on the back of the
refrigerator should be cleaned and tightened at all four
wires.
SectIon 5

dc comPonentS

5.1 door Switches and lamps

Both compartments have interior lights controlled by door
switches. Both lamps are of a halogen type. The lamp
in the freezer compartment is rated at 5 watts, while the
lamp in the fresh food compartment is a 10 watt lamp.
Lamps and switches are directly connected to the power
module. The wires are foamed in and end up in the 10
pin Molex MiniFit P4 connector on the main circuit board.
The lamps are directly controlled from the switches and
the interconnections are on the main board. The proces-
sor on the power module cannot control the lamps but
senses if the switches are closed or not, to decide if doors
are open or closed (Used in the diagnostic mode). The
door switches are open when the switch arm is depressed
(interior light should be off). When the door is open the
switch is closed (interior light should be on). Check that
the switch assembly is properly aligned and that it is not
broken. Check the switch assembly for continuity. To do a
continuity check, first be sure all power is disconnected or
"OFF" to the refrigerator. Second, remove all wires from
the switch assembly, then check the switch. When the
switch is depressed, there should be no continuity. When
the switch is NOT depressed, there should be continuity.
If any of these checks are incorrect, replace the switch.
After the check, be sure the switch assembly is wired
properly per the wiring diagram.
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