Dometic MANUAL REFRIGERATOR User manual

DOMETIC
Dometic
MANUAL REFRIGERATOR
DIAGNOSTIC SERVICE
MANUAL
The
Dometic Corporation
Corporate Office
Warranty
Department
2320 Industrial Parkway
Elkhart, IN 46515
219-295-5228
205 E. Fenn St.
LaGrange, IN 46761
219-463-2191
Technical Services
Department
509 S. Poplar St.
LaGrange, IN 46761
219-463-4858
OS1286 8/89
D-l
Diagnostic Service Manuals
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NOTES:
D-2
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MANUAL REFRIGERATOR
DIAGNOSTIC SERVICE ‘MANUAL
Table of Contents
Page
Diagnostic Flow Charts
No Operation . . . . . . . . . . . . .
No
12OV AC Operation . . . . . . . . .
No Gas Operation (Piezo Igniter) . . . .
No Gas Operation (Automatic Reigniter)
. .
Operation and Diagnosis
Dometic Manual Refrigerators. . . . . . .
Glossary of Terms . . . . . . . . . . . .
Service Bulletins
. . . . . . . . . . . .
D-4-l
D-4-2
D-4-3
D-4-4
D-6- 1
D-8-l
D-9-l
D-3
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MANUAL REFRIGERATOR
DIAGNOSTIC FLOW CHART
NO OPERATION
A.
1
Check Supply Voltage
1. 110 Volt Plug
2. Wire Size
Correct as Necessary
OK
B.
V
Check Fuse Correct as Necessary
NOT OK Replace if Defective
OK
.c.
Check wiring Correct as Necessary
NOT OK
OK
D.
Check Switch NOT OK
Correct as Necessary
(Page D-6-20, Para. 66)
OK
E.
V
Check Thermostat , Correct as Necessary
NOT OK Continuity Check
D-4-l
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MANUAL REFRIGERATOR
DIAGNOSTIC FLOW CHART
NO 120 VOLT AC OPERATION
A.
1. Check AC Power
2. Refrigerator Plugged in
3. Breaker
4. Coach Plug
Correct as Necessary
OK
B.
Check Selector Switch NOT OK
Correct as Necessary
(Page D-6-20, Para. 66)
OK
c.
V
Check Thermostat Correct as Necessary
Continuity Check
NOT OK
OK
D.
Check 120 Volt Heater
NOT OK
Correct as Necessary
Ohm’s Reading
Bulletin #28
(Page D-9-l 4, D-9-l 5)
D-4-2
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MANUAL REFRIGERATOR
DIAGNOSTIC FLOW CHART
NO GAS OPERATION - Models Equipped with Piezo igniter
.
Check Gas Supply
OK
B.
Check Switch
I
NOT OK
Correct as Necessary
(Page D-6-20, Para 66)
OK
.C.
Check Thermostat
OK
D.
V
Check Gas Pressure
OK
NOT OK
NOT OK
Correct as Necessary
Continuity Check
Correct as Necessary
(Page D-6-13, Para. 37)
Check Flue & Burner
NOT OK
Correct as Necessary
No Obstructions
OK
F.
Check Piezo Resistance
I
NOT OK
Correct as Necessary
(Page D-6-l 8, Para. 58)
OK
G.
V
Check Piezo Electrode
I
r
Replace Electrod
(Page D-6-18, 58)
NOT OK
OK
Check Spark Gap Correct as Necessary
of Electrode to Burner NOT OK (Page D-6-19,
Para. 62)
D-4-3
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MANUAL REFRIGERATOR
DIAGNOSTIC FLOW CHART
NO GAS OPERATION - Models Equipped with Automatic Reigniter
A.
Check Gas Pressure
NOT OK
Correct as Necessary
(Page D-6-13, Para 37)
OK
B.
V
Check Gas Supply
I
OK
NOT OK
Correct as Necessary
(Page D-6-14, Para. 40)
C.
Check 12 Volt D.C.
Supply
Correct as Necessary
NOT OK
I
OK
Check Switch
NOT OK
Correct as Necessary
(Page D-6-20, Para. 66)
I
OK
_E.
Check Thermostat
NOT OK
Correct as Necessary
Check for Continuity
OK
F.
V
Clean Assembly &
Check Flue & Burner Orifice as Necessary
NOT OK
I
OK
,G.
Check Electrode
Replace Electrode
(Page D-6-19, Para. 62)
NOT OK
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NOTES:
D-5
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OPERATION & DIAGNOSIS
OF
DOMETIC
MANUAL REFRIGERATORS
D-6-1
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(1)
This is Dometic’s Manual Refrigeration Diagnosis and Troubleshooting program. In this program
we will discuss the way an absorption cooling unit operates, and the diagnostic procedures
used to troubleshoot the complete refrigerator system.
(2)
Before we begin extensive troubleshooting
procedures on the cooling unit, let’s take a few
minutes to see how it operates.
THE ABSORPTION SYSTEM
(3)
The sealed combustion unit contains a
mixture of ammonia, water and a rust
inhibiting agent. After this solution is
introduced into the coils, this unit is
pressurized with hydrogen gas. When
this system is in operation, the am-
monia vaporizes in the hydrogen atmo-
sphere and absorbs heat from inside
the refrigerator.
EVAPORATOR
GAS
TEMPERATURE
EXCHANGER
ABSORBER
VESSEL
BOILER
.
D-6-2
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(4)
The cooling unit parts that accomplish this
‘cooling’ or heat extraction process, include the:
Boiler or Generator
(5)
Condenser
(6)
Evaporator
PUMP
BOILER
l-------------
WATER
SEPARATOR
I
GAS
TEMPERATUR
EXCHANGER
------------
I
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1
D-6-3
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(7)
Absorber
ABSORBER
THE ABSORPTION SYSTEM
CONDENSER
EVAPORATOR
Because the self-contained cooling unit
does not utilize an electric compressor
or pump, the cooling coils can be oper-
ated from a variety of heat sources. LP
gas, 120 volts AC and 12 volts DC
heating elements are the most com-
monly used heat sources for recreation-
al vehicle applications.
TEMPERATURE
EXCHANGER
TEMPERATURE
EXCHANGER _
(9)
Before this cooling system can properly
extract heat from the cabinet of the
refrigerator, three requirements for prop-
er refrigerator operation must be met.
These are precise heat, specified ven-
tilation and proper leveling.
THREE REQUIREMENTS
FOR PROPER OPERATION
1. Level
2. Air Flow (Ventilation)
3. Heat
D-6-4
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(10)
We will now take a closer look at how the
cooling unit functions in normal operation.
When proper heat is supplied to the boiler,
ammonia vapor is produced and rises in the
siphon pump, carrying with it a weak liquid
ammonia solution. As seen from this drawing,
the siphon pump, or pump tube, is an internal
arrangement within the boiler section. The boiler
section utilizes the ammonia-water liquid solu-
tion in the absorber and as it is heated, turns
the solution into a strong ammonia vapor, which
is needed to operate the system. This strong
ammonia vapor rises from the pump tube to the
condenser coil.
Any deviation from the listed amount of
heat to the absorption system will alter the
ammonia to water ratio, which, in turn, will
decrease the cooling unit’s overall efficiency.
The weak ammonia solution which remains
behind is diverted to the top of the absorber
coils to perform a function that we will discuss
in further detail later in the program.
(11)
The air that passes through the condenser fins,
from the venting system, removes heat from the
ammonia vapor, causing it to condense into a
strong liquid ammonia solution. As a liquid, it
then flows to the low temperature evaporator, or
freezer companment, where it comes into
contact with a hydrogen atmosphere. When this
occurs, the ammonia begins to evaporate which
draws heat from inside the freezer section, to
the rear of the cooling unit.
(12)
This heat is then dissipated out through the
upper vent, which allows the refrigerators
interior temperature to properly maintain food
storage requirements. Not all of the liquid
ammonia evaporates in the freezer. What is left
continues to evaporate as it flows to the high
temperature evaporator, or food storage com-
partment.
WATER
I------------------------~
ENSER
PUMP
COLD INTERIOR
D-6-5
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U 3)
As this process continues, the ammonia and
hydrogen vapors become intermixed and flow
downward into the absorber vessel. As the
ammonia vapor comes in close contact to the
liquid ammonia solution in the absorber vessel,
the ammonia is absorbed into the liquid
solution, allowing the hydrogen vapor to rise up
through the absorber coils. After this absorption
process, the vapor consists of mostly hydrogen
with some traces of ammonia.
-------
(14)
To remove the remaining amounts of ammonia
vapor still present in the hydrogen, a
continuous flow of weak ammonia solution is
fed, by gravity, to the top of the absorber coil
from the boiler. As this weak ammonia solution
flows downward through the absorber, it
absorbs the ammonia vapor from the mixture,
allowing the hydrogen vapor to rise through the
absorber coil and return to the evaporator. With
the hydrogen returned to the evaporator and
the ammonia remixed into solution in the
absorber vessel, the cooling process can
continue.
(15)
Now that we have a basic understanding of
proper cooling unit flow and operation, let’s
take a step-by-step look at the three require-
ments for proper cooling unit operation. Please
note it is essential that these three requirements
be diagnosed before attempting to diagnose
the cooling unit. A problem with leveling, heat
input or ventilation may lead you to think that
the cooling unit is faulty, when actually it is not.
This causes an increased expense to you, the
customer, and valuable shop time is wasted
because of incorrect diagnosis, By following
and checking the three unit requirements, costly
diagnostic errors can be eliminated.
---
__------
THREE REQUIREMENTS
FOR PROPER OPERATION
1. Level
2. Air Flow (Ventilation)
3. Heat
D-6-6
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(16)
Since the absorption system utilizes no
mechanical pumps or compressors to circulate
the refrigerant within the system, proper leveling
is required to provide correct refrigerant flow in
the gravity-feed system. Without proper leveling,
refrigerant within the cooling coils will collect
and stagnate at certain areas. When this
happens the cooling process will stop.
(17)
On the older style cooling units equipped with
square boiler box covers, this condition can
cause permanent cooling unit failure. As we can
see from this drawing, square boiler box
cooling units utilize an exposed siphon pump
tube which will become excessively super-
heated in an out-of-level condition. This can
allow the rust inhibiting agent to chemically
break down and permanently block or restrict
the normal refrigerant flow through the pump.
Shaking, tipping or so called ‘burping the
refrigerator will not loosen or dislodge the
blockage. The only recommended service
procedure is to replace the cooling unit. To
prevent this occurrence, proper leveling is of
utmost importance when the RV is parked for
any length of time.
THREE REQUIREMENTS
FOR PROPER OPERATION
1. Level
REFRIGERATOR IS TO BE LEVEL
(18)
To level these units, the spirit or bubble level
LEVELS
should be placed in the approximate front and
center of the floor of the freezer compartment.
The coach should then be positioned so that at
least 3/4 of the bubble is within the required
mark while the refrigerator is in operation.
REMEMBER: Failure to property level a square
boiler box can result in alack of cooling or
permanent damage to the coding unit. When
the vehicle is moving, leveling is not critical as
the rolling and pitching movement of the RV will
keep the solution in motion, preventing the
solution from accumulating in the piping. --
-
D-6-7
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(19)
In recent years Dometic has engineered a new
type of cooling unit that utilizes an improved
siphon pump tube design which drastically
reduces the possibility of permanent damage to
the coils if operated in an out-of-level condition,
or too much heat is generated at the boiler
section. As we can see from this drawing, the
siphon pump tube is enclosed in the design
and is surrounded by a weak ammonia solution,
which will protect the pump tube from abnor-
mally over-heating. This type of unit; however,
does not eliminate the need for proper leveling.
The unit still requires gravitational flow to
provide the proper cooling process, and if
leveling is outside the necessary limits, cooling
will dramatically slow down or stop completely.
The cooling coils are not normally damaged in
this fashion and once proper leveling is main-
tained, the cooling process will resume.
(20)
Spirit or bubble levels are no longer being
supplied with the new style refrigerators as the
RV or vehicle only needs to be leveled so it is
comfortable to live in, with no noticeable sloping
of the floor or walls. For diagnosis, the new
style cooling
units that incorporate the
protection boiler system, can be differentiated
from the older style coils by the shape and
design of the outer boiler box cover on the rear
of the cooling unit. These units will incorporate
a circular metal cover,
. . .
while the older style utilizes a square
shaped enclosure.
We will discuss diagnosis
and troubleshooting of these units in more
detail later in the program.
PUMP
I
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I
I
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I
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(22)
The coach vent system must be able to provide
a way to direct the hot air, produced by the
action of the cooling unit, out away from the
installation of the refrigerator.
(23)
In a good installation there should be as little
open space as possible surrounding the sides
and top of the refrigerator to achieve proper air
flow. All potential dead air pockets should be
blocked or baffled to insure that heat from the
cooling unit won’t be trapped in these spaces
and reduce efficiency. In addition, the cooling
unit should be at least one inch from the
nearest surface made of combustible materials.
Please follow the installation manual for proper
dimensions and clearances.
RVIA requires that the refrigerator be
installed in such a manner as to provide
complete separation of the combustion system
and the interior atmosphere of the recreational
vehicle. This regulation requires all seams and
joints in the enclosure be sealed. The under-
counter installation is different. The addition of
a metal chute the width of the enclosure, that
extends from the upper side vent, will help
eliminate the possibility of dead air pockets. It
helps direct the hot air out the exhaust vent.
The best method for venting the absorption
refrigerator is with a lower side vent and a roof
vent. Using proper Dometic vents will give you
sufficient intake and exhaust areas for ventila-
tion
(24)
Heat application to the boiler section of the
cooling unit must be within the designed BTU’s.
Never oversize the heating element on AC or
DC power source. Always use the proper size
orifice for gas modes. As explained earlier, any
deviation will cause a potential cooling unit
failure.
THREE REQUIREMENTS
FOR PROPER OPERATION
1. Level
2. Air Flow (Ventilation)
--------
-----
1
II
0" CLEARANCE
1" FROM
AIR FLOW
I
I
II
------------
J
THREE REQUIREMENTS
FOR PROPER OPERATION
1. Level
2. Air Flow (Ventilation)
3. Heat
D-6-9
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(25)
Three things must be remembered
when diagnosing a cooling unit:
First, circulation within the cool-
ing unit is totally gravitational. This
means proper leveling is important.
Second, heat - created to boil
the ammonia -
now has to be dis-
sipated into the surrounding air. Heat
from the absorber and condenser must
also be dissipated so as to cool the
ammonia sufficiently.
Third, proper heat application at
the boiler section.
THE ABSORPTION SYSTEM
(26)
When diagnosing a cooling unit, remember this
is the only part we cannot field check with test
equipment, yet it is the simplest and quickest
part to diagnose.
CONDENSER
EVAPORATOF
TEMPERATURE
EXCHANGER
BOILER
DIAGNOSING
THE
COOLING UNIT
(27)
After the unit has been operating for
approximately one hour, carefully touch the unit
at the boiler box and the absorber area. These
areas should be approximately the same
temperature, regardless of the ambient
temperature. Equal heat between the boiler and
the absorber indicates the fluid circulation within
the unit is good.
TEMPERATURE
GOOD CIRCULATION
D-6-10
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(28)
One of the faults with a cooling unit is
a blockage. This can happen when the
unit is operated off-ievel, or if too much
heat has been applied to the boiler
area. To the touch, this unit will be
extremely hot at the boiler with little
warmth at the absorber. In other words,
no circulation.
(29)
This type of fault means a lost charge.
It is known as a ‘leaker’. To the touch,
this unit will be warm at the boiler and
extremely hot at the absorber. In this
condition we are still boiling ammonia
but have no hydrogen for evaporation.
(30)
The following section of the program
examines the Dometic manual refriger-
ator’s gas and electrical systems.
Dometic refrigerators are designed for
both piezo and automatic ignition. Both
systems will be covered in this presen-
tation.
T
BOILER
HOT GAS ONLY
WARM
BOILER
D-6-1 1
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(31)
Let’s look at the current Dometic refrigerators
and see how the gas flows.
(32)
Gas flows from the gas line to the shut-off valve
and to the connection piece.
(33)
into the combination gas and electric thermostat
(34)
through the safety valve thermocouple
(35)
test housing
UNDERSTANDING
THE
GAS SYSTEM
SHUT-OFF
VALVE
IGAS LINE
CONNECTION
PIECE
COMBINATION
GAS & ELECTRIC
THERMOSTAT
SAFETY VALVE/
PRESSURE
TEST
HOUSING
D-6-12
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