U.S. patent application number 09/900434 was filed with the patent office on 2001-12-27 for control system and related methods for refrigeration and freezer units.
Invention is credited to Davis, Ronald, Lewis, Laura, Slade, Alvin.
Application Number | 20010054292 09/900434 |
Document ID | / |
Family ID | 23904458 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054292 |
Kind Code |
A1 |
Davis, Ronald ; et
al. |
December 27, 2001 |
Control system and related methods for refrigeration and freezer
units
Abstract
A cooling system and related method of defrosting a
refrigeration unit or a freezer unit involves the steps of (a)
monitoring a compressor running time, (b) monitoring an evaporator
coil temperature, (c) monitoring a first time period since a last
cooled compartment door open alarm of the unit, (d) monitoring a
second time period since a last defrost operation, (e) monitoring a
third time period during which the cooled compartment door is
closed, and (f) controlling initiation of a defrost operation as a
function of the monitored compressor running time, the monitored
evaporator coil temperature, the monitored first time period, the
monitored second time period, and the monitored third time period.
Various sets of conditions may be established for triggering
initiation of the defrost operation. The system may also detect
refrigerant leaks and a clogged condenser as a function of
compressor running time and compressor discharge line
temperature.
Inventors: |
Davis, Ronald; (Euless,
TX) ; Lewis, Laura; (Lipan, TX) ; Slade,
Alvin; (Forest Hill, TX) |
Correspondence
Address: |
THOMPSON HINE L.L.P.
2000 COURTHOUSE PLAZA , N.E.
10 WEST SECOND STREET
DAYTON
OH
45402
US
|
Family ID: |
23904458 |
Appl. No.: |
09/900434 |
Filed: |
July 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09900434 |
Jul 6, 2001 |
|
|
|
09479545 |
Jan 7, 2000 |
|
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Current U.S.
Class: |
62/154 ;
62/234 |
Current CPC
Class: |
F25B 2700/21152
20130101; F25B 2500/222 20130101; F25B 2700/02 20130101; F25D
2700/02 20130101; F25D 21/006 20130101; F25D 2700/12 20130101; F25D
21/002 20130101; F25D 2700/10 20130101 |
Class at
Publication: |
62/154 ;
62/234 |
International
Class: |
F25D 021/06; F25D
021/00 |
Claims
What is claimed is:
1. A method for controlling defrost of a refrigeration unit or a
freezer unit, the method comprising the steps of: (a) monitoring a
compressor running time; (b) monitoring a time period since a last
defrost operation; (c) initiating a defrost operation if the
following conditions are met: (i) the monitored compressor running
time exceeds a threshold running time; and (ii) the monitored time
period since the last defrost operation exceeds a threshold time
period.
2. The method of claim 1 wherein the threshold running time is
determined based at least in part upon an average compressor
running time for a preceding time period.
3. The method of claim 2 wherein the threshold running time
comprises the average compressor running time increased by a
predetermined amount.
4. The method of claim 1 wherein the threshold last defrost time
period is of sufficient length to assure a temperature of a cooled
compartment of the unit remains below a threshold maximum
temperature level.
5. A method for controlling defrost of a refrigeration unit or a
freezer unit, the method comprising the steps of: (a) monitoring an
evaporator coil temperature; (b) monitoring a first time period
since a last cooled compartment door open alarm of the unit; (c)
monitoring a second time period since a last defrost operation; and
(d) initiating a defrost operation if the following conditions are
met: (i) the monitored evaporator coil temperature exceeds a
threshold coil temperature; (ii) the first monitored time period
exceeds a first threshold time period; and (iii) the second
monitored time period exceeds a second threshold time period.
6. The method of claim 5 wherein the threshold coil temperature is
determined based at least in part upon a lowest occurring coil
temperature since the last defrost operation.
7. The method of claim 6 wherein the threshold coil temperature
comprises the lowest occurring coil temperature increased by a
predetermined amount.
8. A method for controlling defrost of a refrigeration unit or a
freezer unit, the method comprising the steps of: (a) monitoring an
evaporator coil temperature; (b) monitoring a first time period
since a last cooled compartment door open alarm of the unit; (c)
monitoring a second time period since a last defrost operation; (d)
monitoring a third time period during which the cooled compartment
door is closed; and (e) initiating a defrost operation if the
following conditions are met: (i) the monitored evaporator coil
temperature exceeds a threshold coil temperature; (ii) the first
monitored time period is less than a first threshold time period;
(iii) the second monitored time period exceeds a second threshold
time period; and (iv) the third monitored time period exceeds a
third threshold time period.
9. The method of claim 8 wherein the third threshold time period is
sufficient to allow the coil temperature to stabilize after the
cooled compartment door is closed and when the coil does not have
excessive frost build up.
10. A method for defrosting a refrigeration unit or a freezer unit,
the method comprising the steps of: (a) monitoring a compressor
running time; (b) monitoring an evaporator coil temperature; (c)
monitoring a first time period since a last cooled compartment door
open alarm of the unit; (d) monitoring a second time period since a
last defrost operation; (e) monitoring a third time period during
which the cooled compartment door is closed; and (f) controlling
initiation of a defrost operation as a function of the monitored
compressor running time, the monitored evaporator coil temperature,
the monitored first time period, the monitored second time period,
and the monitored third time period.
11. The method of claim 10 wherein in step (f) the defrost
operation is initiated if at least one of the following three sets
of conditions exist: (1) first condition set: (i) the monitored
compressor running time exceeds a threshold running time; and (ii)
the second monitored time period exceeds a second threshold time
period; (2) second condition set: (i) the monitored evaporator coil
temperature exceeds a threshold coil temperature; (ii) the first
monitored time period exceeds a first threshold time period; and
(iii) the second monitored time period exceeds the second threshold
time period; (3) third condition set: (i) the monitored evaporator
coil temperature exceeds a threshold coil temperature; (ii) the
first monitored time period is less than the first threshold time
period; (iii) the second monitored time period exceeds the second
threshold time period; and (iv) the third monitored time period
exceeds a third threshold time period.
12. A method of monitoring a refrigeration system for a refrigerant
leak, the method comprising the steps of: (a) monitoring a
compressor running time; (b) monitoring a temperature of a
discharge line of the compressor; (c) controlling activation of a
line leak alarm based at least in part upon: (i) the monitored
compressor running time exceeding a threshold running time; and
(ii) comparison of the monitored discharge line temperature to a
threshold discharge line temperature.
13. The method of claim 12 wherein in step (c) the line leak alarm
is activated if the monitored discharge line temperature does not
exceed the threshold discharge line temperature.
14. The method of claim 13 wherein the threshold discharge line
temperature is determined based at least in part upon an initial
discharge line temperature measured when the compressor running
time begins.
15. The method of claim 13 wherein the determined line temperature
comprises the initial discharge line temperature increased by a
predetermined amount.
16. A method of monitoring air to a condenser of a cooling system,
the method comprising the steps of: (a) monitoring a running time
of a compressor; (b) monitoring a temperature of a discharge line
of the compressor; (c) controlling activation of a clogged
condenser alarm based at least in part upon: (i) the running time
of the compressor exceeding a threshold running time; and (ii)
comparison of the monitored discharge line temperature to a
threshold discharge line temperature.
17. The method of claim 16 wherein in step (c) the clogged
condenser alarm is activated if the monitored discharge line
temperature exceeds the threshold discharge line temperature.
18. The method of claim 17 wherein the threshold running time is
indicative of a clogged condenser and wherein the threshold line
temperature is indicative of a clogged condenser.
19. A control system for a refrigeration unit or a freezer unit,
comprising: an electronic controller including: a first input for
receiving a signal indicative of an open/closed status of a cooled
compartment door of the unit; a second input for receiving a signal
indicative of a temperature of an evaporator coil of the unit; a
first output for triggering operation of a compressor of the unit;
a third input for receiving a signal indicative of a temperature of
a discharge line of the compressor; wherein the electronic
controller is operable to: monitor a running time of the
compressor; monitor the evaporator coil temperature; monitor the
discharge line temperature; track a first time period running from
a last defrost operation of the unit; track a second time period
running from a last cooled compartment door open alarm of the unit;
and track a third time period running from when the cooled
compartment door was last closed.
20. The system of claim 19 wherein the electronic controller is
operable to control initiation of a defrost operation by inhibiting
operation of the compressor as a function of the monitored
compressor running time, the monitored evaporator coil temperature,
the monitored first time period, the monitored second time period,
and the monitored third time period.
21. The system of claim 20 wherein the electronic controller
further comprises: a second output for activating a refrigerant
system leak alarm and a third output for activating a clogged
condenser alarm; wherein the electronic controller is operable to
control activation of the system leak alarm based at least in part
upon the monitored compressor running time and the monitored
discharge line temperature; and wherein the electronic controller
is operable to control activation of the clogged condenser alarm
based at least in part upon the monitored compressor running time
and the monitored discharge line temperature.
Description
TECHNICAL FIELD
[0001] This invention pertains generally to refrigeration and
freezer units, and more specifically to a control system for such
units and related methods for controlling defrost, monitoring the
status of a system condenser coil, and monitoring for refrigerant
leaks.
BACKGROUND OF THE INVENTION
[0002] Cooling systems are utilized in many different types of
refrigeration units and freezer units. For example, commercial
refrigeration and freezer units used by those in the food industry
such as restaurants generally include some variation of the
standard cooling system which has existed for many years.
Similarly, numerous control schemes for such cooling systems are
known, including control schemes for defrost operations of the
cooling systems in order to eliminate frost build up on the
evaporator coils of such systems. However, improvements in such
defrost control schemes are continually sought.
[0003] One problem associated with such cooling systems is that air
is generally passed through a condenser to remove heat from the
refrigerant. The intake air to the condenser passes through the
condenser coil. As particulates build up on the condenser, air flow
through the coil decreases and system efficiency may be reduced.
Accordingly, it would be desirable to provide the ability to detect
a clogged condenser in order to clean the condenser when
needed.
[0004] Another problem associated with such cooling systems is the
occurrence of refrigerant leaks in the system. Accordingly, it
would be desirable to provide the ability to detect such
refrigerant leaks.
SUMMARY OF THE INVENTION
[0005] In one aspect of the present invention, a method of
defrosting a refrigeration unit or a freezer unit involves the
steps of (a) monitoring a compressor running time, (b) monitoring
an evaporator coil temperature, (c) monitoring a first time period
since a last cooled compartment door open alarm of the unit, (d)
monitoring a second time period since a last defrost operation, (e)
monitoring a third time period during which the cooled compartment
door is closed, and (f) controlling initiation of a defrost
operation as a function of the monitored compressor running time,
the monitored evaporator coil temperature, the monitored first time
period, the monitored second time period, and the monitored third
time period. Various sets of conditions may be established for
triggering initiation of the defrost operation.
[0006] In another aspect of the invention a method of monitoring a
refrigeration system for refrigerant leaks involves (a) monitoring
a running time of a compressor, (b) monitoring a temperature of a
discharge line of the compressor, (c) controlling activation of a
line leak alarm based at least in part upon: (i) the running time
of the compressor exceeding a threshold running time; and (ii)
comparison of the discharge line temperature to a threshold
discharge line temperature.
[0007] Yet a further aspect of the invention provides a method of
monitoring the condenser of a cooling system. The method involves
(a) monitoring a running time of a compressor, (b) monitoring a
temperature of a discharge line of the compressor, (c) controlling
activation of a clogged condenser alarm based at least in part
upon: (i) the running time of the compressor exceeding a threshold
running time; and (ii) comparison of the discharge line temperature
to a threshold discharge line temperature.
[0008] An electronic controller may be utilized to implement the
foregoing methods in conjunction with various sensors associated
with the system components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a partial schematic of a cooling system;
[0010] FIG. 2 is a high-level flow chart of system defrost control
operation;
[0011] FIG. 3 is a high-level flow chart of clogged condenser
detection operation; and
[0012] FIG. 4 is a high-level flow chart of refrigerant leak
detection operation.
DETAILED DESCRIPTION
[0013] Referring to FIG. 1, a high-level schematic of a
refrigeration system 10 is shown. The refrigeration system 10
includes a compressor 12, a condenser 14, a refrigerant chamber 16
and an evaporator 18 which typically includes an evaporator coil.
As a refrigerant fluid within the system 10 enters the evaporator
18, the fluid is cooler than the surrounding area. This surrounding
area is established by, or is in communication with a cooled
compartment 20 in which items such as food products are kept cool
or frozen. In the evaporator, refrigerant fluid in liquid form
absorbs heat from the compartment 20 and vaporizes. The vaporized
refrigerant is then forced into the compressor 12 where its
temperature increases as a result of compression. The compressed
coolant vapor passes to the condenser 14 where it cools down and
liquifies as heat is transferred to the cooler air. In this regard,
intake air 24 to the condenser 14 is typically passed through or
over cooling coils of the condenser. The air flow may be generated
by a fan unit (not shown).
[0014] The cooled compartment 20 includes a door 26 which provides
access to the compartment. A switch 28 is situated to generate a
signal indicative of the open/closed status of the door 26. A
temperature sensor 30 is provided for generating signals indicative
of the evaporator coil temperature. A combination
temperature/humidity sensor 32 may also be provided for generating
a signal indicative of the temperature and relative humidity of the
ambient air in or around the cooled compartment 20. Separate
sensors could also be utilized. A temperature sensor 34 is also
provided at the discharge line of the compressor for generating
signals indicative of the discharge line temperature. The
temperature sensors may be of any suitable type known in the
art.
[0015] An electronic controller 36 is provided for controlling the
operations of the cooling system 10. Controller 36 may have various
configurations but will typically include some type of processor
such as a micro-processor, micro-controller, or ASIC, along with
associated memory such as RAM, ROM, and/or EEPROM, and one or more
associated timers or clocks. The controller 36 also includes
input/output circuitry for interfacing with the various system
components via electrical connections therewith. For example, the
controller receives and interprets signals from sensors 28, 30, 32,
and 34. The controller also controls activation of the compressor
12 via connection thereto, or via connection between the compressor
and a power source (not shown). The controller 36 may also be
connected to output devices 38 and 40 which may be annunciators or
alarms such as light emitting elements or sound emitting elements
the energization of which is controlled by the controller 36. The
elements 38 and 40 may be separate from the controller or may be
located in proximity to the controller 36 within the same housing.
It is recognized that the cooling system 10 may include various
other components and sensors which are unrelated to the various
aspects of the invention. Given the foregoing system 10, the
various aspects of the present invention are explained below.
[0016] Reference is now made to the defrost control flow chart 50
of FIG. 2. Preferably, the controller is configured to initiate
regular defrost operations at standard intervals. The standard
interval may be stored in memory of the controller, and various
intervals may be stored in memory to be selected according to
operating conditions of the system 10. Operation according to the
flow chart 50 enables an intermediate defrost operation to be
initiated between the regular defrost operations if necessary.
However, the control scheme of flow chart 50 could also be utilized
in systems where defrost operations are not initiated at standard
intervals.
[0017] In FIG. 2 the following nomenclature is utilized:
[0018] "LDTP" stands for "last defrost time period" and represents
the length of time which has passed since the end of the last
defrost operation;
[0019] "TLDTP" stands for "threshold last defrost time period";
[0020] "CRT" stands for compressor running time and represents the
length of time during which the compressor runs during a cooling
cycle of the system;
[0021] "TRT" stands for "threshold running time";
[0022] "LDATP" stands for door "last door alarm time period" and
represents the length of time which has passed since end of the
last cooled compartment door open alarm;
[0023] "TLDATP" stands for "threshold last door alarm time
period";
[0024] "DCTP" stands for "door closed time period" and represents
the length of time which has passed since the cooled compartment
door was last closed;
[0025] "TDCTP" stands for "threshold door closed time period";
[0026] "ECTEMP" stands for "evaporator coil temperature" and
represents the temperature of the evaporator coil as sensed by
temperature sensor 30; and
[0027] "TCTEMP" stands for "threshold coil temperature."
[0028] The routine of flow chart 50 may be executed periodically to
determine whether or not to initiate a defrost operation. The
routine will typically be initiated during a cooling cycle of the
system 10, that is, when the compressor 12 is running. When called
upon the routine begins at block 52 and moves to block 54 where the
last defrost time period is compared to a threshold last defrost
time period. The threshold last defrost time period is preferably
established as a time period which is long enough to assure that
the average temperature within the cooled compartment 20 does not
exceed a desired level if another defrost operation is performed.
For example, it is possible that if two defrost operations are
performed in quick succession the average temperature of the cooled
compartment may raise above a desired level for an unacceptable
length of time. Accordingly, if the last defrost time period is not
greater than the threshold last defrost time period, the routine is
exited at block 56 and no defrost operation is performed.
[0029] On the other hand, if the last defrost time period is
greater than the threshold last defrost time period the routine
moves to block 58 where the compressor running time is compared to
a threshold running time. The compressor running time may be
maintained by a timer associated with the controller 36. The
threshold running time is established as a time which indicates
that the compressor has run longer than it should have to in order
to cool, representing a build up of frost on the evaporator coil.
Preferably, the threshold running time is established by the
electronic controller based upon a running average of compressor
running times over a preceding time period such as thirty-six
hours. The running average may be incremented by some predetermined
amount such as twenty-five percent. However, this percent is merely
representative and it is recognized that the exact percent could be
established for a given unit or system 10 based upon testing. If
the compressor running time exceeds the threshold running time the
routine moves to block 60 and a defrost operation is initiated. If
the compressor running time does not exceed the threshold running
time, the routine moves to block 62.
[0030] At block 62 the last door alarm time period is compared to a
threshold last door alarm time period. The threshold last door
alarm time period is established to account for increases in
evaporator coil temperature which might result from the door
remaining open for an excessive period of time, and again may be
established by testing. If the last door alarm time period is not
less than the threshold last door alarm time period, the routine
moves to block 64 where the evaporator coil temperature is
evaluated. If the current evaporator coil temperature is greater
than a threshold coil temperature then the routine moves to block
60 and a defrost operation is initiated. The threshold coil
temperature is established as a temperature indicative of frost
build up on the evaporator coil and is preferably set at a value
which is dependent upon the lowest evaporator coil temperature
since the end of the last defrost operation. For example, the
threshold coil temperature may be established automatically by the
controller as the lowest evaporator coil temperature since the last
defrost operation incremented by a certain amount. If the current
evaporator coil temperature at block 64 is not greater than the
threshold coil temperature, the routine is exited at block 56 and
no defrost operation is performed.
[0031] Returning to block 62, if the last door alarm time period is
less than the threshold last door alarm time period the routine
moves to block 66 where the open/closed status of the door 26 is
checked. If the door 26 is not closed the routine is exited at
block 56 and no defrost operation is performed because it is
undesirable to perform a defrost operation when the door is open.
If the door 26 is closed the routine moves to block 68 and the door
closed time period is compared with a threshold door closed time
period. The threshold door closed time period is preferably
established as a time period of sufficient length to allow the
evaporator coil temperature to cool down and stabilize after the
door has been open for an excessive period of time and may be
determined by testing of the particular unit and system 10. If the
door closed time period does not exceed the threshold door closed
time period the routine moves to block 56 and no defrost operation
is performed. However, if the door closed time period exceeds the
threshold door closed time period the routine moves to block 64 and
a determination of whether or not to initiated a defrost operation
is made as described above.
[0032] The routine described in flow chart 50 therefore provides a
defrost control system and method in which the compressor running
time, evaporator coil temperature, last door alarm time period,
last defrost time period, and door closed time period are monitored
and in which initiation of a defrost operation is controlled as a
function of the compressor running time, evaporator coil
temperature, last door alarm time period, last defrost time period,
and door closed time period. Preferably, a defrost operation is
initiated when one or more of three sets of conditions exist.
Namely, condition set 1 in which the compressor running time
exceeds the threshold running time and the last defrost time period
exceeds the threshold last defrost time period; condition set 2 in
which the evaporator coil temperature exceeds the threshold coil
temperature, the last defrost time period exceeds the threshold
last defrost time period, and the last door alarm time period
exceeds the threshold last door alarm time period; and condition
set 3 in which the evaporator coil temperature exceeds the
threshold coil temperature, the last defrost time period exceeds
the threshold last defrost time period, the last door alarm time
period is less than the threshold last door alarm time period, and
the door closed time period exceeds the threshold door closed time
period.
[0033] The electronic controller is programmed or otherwise
configured to control defrost according to the flow chart 50. The
electronic controller 36 may initiate a defrost operation by
inhibiting operation of the compressor 12. The length of a given
defrost operation may be predetermined or may vary upon other
monitored parameters of the system 10. As described herein
initiation of a defrost operation may include starting the defrost
operation immediately when block 60 of flow chart 50 is reached,
but may also include setting a flag which will cause the defrost
operation to start after the compressor 12 stops running during a
cooling sequence.
[0034] Referring now to FIG. 3, an additional feature of the system
10 is described and provides the ability to determine when the
condenser 14 of the system becomes clogged. The following
nomenclature is utilized in FIG. 3:
[0035] "CRT" stands for compressor running time and represents the
length of time during which the compressor runs during a cooling
cycle of the system;
[0036] "TRT.sub.CF" stands for "threshold running time" indicative
of a clogged condenser;
[0037] "DLT" stands for "discharge line temperature" of the
compressor; and
[0038] "TDLT.sub.CF" stands for "threshold discharge line
temperature" indicative of a clogged condenser.
[0039] The routine of flow chart 70 begins at block 72 and moves to
block 74 where operation of the compressor 12 is started. At block
76 a timer for monitoring the compressor running time is started.
At block 78 the compressor running time is compared to a threshold
running time which is indicative of a clogged condenser. The
threshold running time may be established by testing of the unit
and system, by tracking prior compressor running times, or a
combination of the two. If the compressor running time exceeds the
threshold running time the routine moves to block 80 where the
discharge line temperature is compared to a threshold discharge
line temperature indicative of a clogged condenser. The threshold
discharge line temperature may be established by testing of the
unit and system, by tracking prior discharge line temperatures, or
a combination of the two. If the discharge line temperature exceeds
the threshold discharge line temperature then an alarm is initiated
at block 82. The discharge line temperature check is provided to
verify that the excessive compressor running time is not due to a
compressor malfunction such as a refrigerant leak or otherwise
caused low refrigerant level as discussed in more detail below. The
alarm may be activation of one of the sound element or light
element 38 or 40, or may merely be a flag which is set in memory
for later retrieval. If the compressor discharge line temperature
does not exceed the threshold discharge line temperature, the
routine moves to block 84 where other processing may continue.
Referring again to block 78, if the compressor running time does
not exceed the threshold running time the routine moves to block 86
where other control operations and tasks may be performed before
the routine again moves to block 78. The routine of flow chart 70
may be continuously or periodically run during a cooling cycle of
the system 10.
[0040] In FIG. 4 a flow chart 100 depicts a routine for determining
when a refrigerant leak exists in the system 10. The following
nomenclature is utilized in FIG. 4:
[0041] "CRT" stands for compressor running time and represents the
length of time during which the compressor runs during a cooling
cycle of the system;
[0042] "TRT.sub.LL" stands for "threshold running time" indicative
of a line leak in the system;
[0043] "DLT" stands for "discharge line temperature" of the
compressor; and
[0044] "TDLT.sub.LL" stands for "threshold discharge line
temperature" indicative of a refrigerant line leak.
[0045] The routine of flow chart 100 begins at block 102 and moves
to block 104 where operation of the compressor 12 is started. At
block 106 a timer for monitoring the compressor running time is
started. At block 108 the initial discharge line temperature (IDLT)
is checked and recorded or stored in memory. At block 110 the
compressor running time is compared to a threshold running time
which is indicative of a refrigerant line leak. The threshold
running time may be established by testing of the unit and system,
by tracking prior compressor running times, or a combination of the
two. If the compressor running time exceeds the threshold running
time the routine moves to block 112 where the discharge line
temperature is compared to a threshold discharge line temperature
indicative of a refrigerant line leak. Preferably, the threshold
discharge line temperature is based upon the initial discharge line
temperature incremented by a predetermined amount established by
testing. If the discharge line temperature does not exceed the
threshold discharge line temperature then an alarm is initiated at
block 114. This scenario is indicative of a refrigerant leak
because the discharge line temperature should rise after compressor
start up due to an increase in system pressure. If the refrigerant
level is low--or if there is a leak in the system, the pressure
cannot build and therefore the discharge line temperature will not
increase as it should. The alarm may be activation of one of the
sound element or light element 38 or 40, or may merely be a flag
which is set in memory for later retrieval. If the compressor
discharge line temperature does exceed the threshold discharge line
temperature, the routine moves to block 116 where other processing
may continue. Referring again to block 110, if the compressor
running time does not exceed the threshold running time the routine
moves to block 118 where other control operations and tasks may be
performed before the routine again moves to block 110. The routine
of flow chart 100 may be continuously or periodically run during a
cooling cycle of the system 10.
[0046] Regarding the routines of flow charts 70 and 100, it is
recognized that an excessive compressor running time could be
indicative of a need for a defrost operation instead of a clogged
condenser or refrigerant line leak. Therefore, in each routine a
back-up check of the discharge line temperature is provided. Based
upon known system performance under various circumstances, and the
combination these two system checks, both clogged condensers and
refrigerant leaks can be effectively monitored and detected. Given
the similarity between the two routines, it is recognized that a
single routine which simultaneously checks for the clogged
condenser and the refrigerant leak could be provided.
[0047] While the forms of the apparatus herein described constitute
preferred embodiments of the invention, it is to be understood that
the invention is not limited to these precise forms of apparatus,
and changes may be made therein without departing from the scope of
the invention.
* * * * *