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Патент USA US3093987

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June 18, 1963
Filed Sept. 15, 1961 ‘
73 i/.
.23 2
United States Patent
Waldemar W. Liehrecht, Emerson, N..l., assignor to Min
neapolis-Honeywell Regulator Company, Minneapolis,
Minn, a corporation of Delaware
Filed Sept. 13, 1961, Ser. No. 137,810
4 Claims. (62-208)
Patented June 18, 1963
FIGURE 2 is a portion of the complete control circuit
to more clearly illustrate the operation of the present in
Referring to FIGURE 1, ‘a space 10 is adapted to be
air conditioned. The ‘air from the space is circulated
through an evaporator or cooling coil :11 by a fan 12
by passing into a return duct 13‘ and exhausting into
the space by a supply duct 14. A motor 15- which is
connected to a source of electrical power drives fan 12.
The present invention is concerned with tan improve 10
Mounted outside the building 20 containing space 10
ment in an air conditioning control system; in particular,
is a remote air cooled “pumpfdown” motor driven re
the improvement is in the con-trol circuit for the re
frigeration apparatus 21. The refrigeration apparatus is
frigeration apparatus to provide remote manual reset of
generally located with respect to space 10 in a manner to
overload or high pressure lock out. '
With the popularity of air conditioning, there have
been many improvements in airconditioning installa
tions to provide more improved air conditioning. One
of the problems faced with residential air conditioning
cut down noise which might ‘be developed by apparatus
21. The apparatus is also generally located outdoors
to most economically obtain outdoor air :for condenser
cooling. A motor driven compressor 22 and a condenser
coil 23 are connected to the evaporator coil to form ‘a
is the noise of the motor compressor. To cut down the
conventional refrigeration system, such ‘as shown in the
amount of noise in the home, the motor compressor and 20 A. B. Newton Patent 2,214,700. The pipe connections
condenser with the condenser fan have often been placed
of the refrigeration system are traced ‘as follows: from
outdoors. In addition, ‘air cooled condenser systems are
evaporator ‘11, a suction pipe 23, motor compressor 22,
usually most economically installed with the compressor
a pipe 24, condenser coil 23‘, a pipe 25, a valve 30, and
and {high side located outdoors. When this refrigeration
back to coil ‘11. Upon the energization of motor com
apparatus is outdoors exposed to colder temperatures, 25 pressor 22, refrigerant is pumped into condenser 23,
“compressor slugging,” which is a result of the migration
and as the heat is removed from the compressed ‘gas by
of the refrigerant in the system to the cold compressor,
air circulating through condenser 23 under the power of
may occur and causes numerous problems. One method
to overcome the compressor slugging is in the use of a
fan 31, the refrigerant condenses to a liquid to ?ow
“pump-down” system which has a valve in the refrigerant 30
line near the evaporator. The valve is controlled by a
space thermostat in the home. The motor driven com
A relay or contactor 32 has an energization winding
33 and a pair of normally open switches 34- and 35.
Switches 34 and 35 close an energization circuit [for
pressor is controlled from a low-pressure switch in the
motor compressor 22 whenever relay 32 is energized. A
through pipe 25 into coil 11 when valve 30' is opened.
refrigeration line to maintain the pressure :on the down
conventional current overload or abnormal condition
stream side of the compressor at some low value. When 35 responsive switch 40 provides an open circuit between ter
the space thermostat is satis?ed, and the valve in the . minals 41 and 42 whenever the current passing through
refrigeration line closes, the motor compressor will op
the circuit of conductors 43 and 44 exceeds some predeter~
erate until the pressure in the suction line is reduced to
mined value. Current overload switch 40 is connected
the low value. Also the compressor may start at ‘any
inthe power supply circuit for compressor 22 as follows:
time to maintain the low pressure which may be depleted 40 from a source of power 415, a conductor 5%, switch 35,
by the valve leakage.
conductor 43; conductor 44, motor compressor ‘22, a
To control such a remote “pump-down” motor driven
conductor 51, switch 34, and back to the source of power
comppressor refrigeration unit with a safety circuit which
through a conductor 52. Fan motor 31 is connected in
is commonly known as the “high impedance” reset cir
parallel with motor compressor 22 to be simultaneously
cuit, the resetting operation of the “high impedance” 45 energized. A high pressure cutout switch 76 is connected
circuit can not be done directly from the space thermostat
as the space thermostat does not have direct control over
the energization circuit for the motor compressor control
ahead of the condenser 23 by a conduit 77. This switch
provides an open circuit between terminals 78‘ and 79
if a pressure above some predetermined value should
occur in pipe 25.
The present invention is concerned with a speci?c im 50
An impedance relay 53 has an energization winding
provement to the “high impedanw” reset circuit to pro
54, ‘and a normally closed switch 55. Relay 53 is en
vide for remote reset whenever the circuit of the high
ergized and locks out the motor contactor 32 upon the
impedance relay is momentarily broken.
opening of current overload switch 4th or high refrigerant
An object of the present invention is to provide an
pressure limit switch 76‘. A momentarily open circuit or
improved air conditioning control circuit wherein a re 55 wide gap relay means '60 has an energization winding 61.
setting action is obtained by a switch means which mo
Relay 61 has a switch 62 which is made up of contacts
mentarily breaks a resetting circuit.
'63 and 64 and a movable member '65 moved‘ between
Another object of the present invention is to provide
the two contacts upon the energization or de-energization
an improvement in the “high impedance” reset circuit
of relay 60. While there are ‘other forms of a wide gap
when the circuit is used with a remote “pump-down” 60 or momentarily open switch means, relay 60 provides a
motor compressor unit so a resetting action of the con
momentarily open circuit whenever the relay means is
trol circuit can be obtained from a remote switch; how
ever, the control circuit and pump-down ‘function will
not be inoperative if an open or short exists in the cir
cuit of the remote reset switch or if the manual reset
switch is left in either the open or closed position.
These and other objects of the present invention will
become apparent upon the study of the following speci?
cation and drawings of which
either ‘dc-energized or energized.
A low pressure cut-off switch 70 is connected by a
pipe 71 to'suction line 23. Switch 70 provides an open
circuit between terminals 72 and 73 whenever the pres
sure in suction line 23 reaches some predetermined low
value. ‘Low pressure cut-off switches ‘of this type‘have
been used to control motor compressors for a number of
years. One particular switch of this type is shown in the
FIGURE 1 is a schematic representation of a typical 70 Kronmiller Patent 2,377,503.
air conditioning installation with the improved control
The energization circuit of relay 32 is traced as fol
lows: from source of power 45, a conductor 74, terminal
72, terminal 73, a conductor St), winding 33, a terminal
81, winding 54, switch 62, and back to the source of
power through a conductor 82. The connection through
switch 62 is made by connecting contacts 63 and 64 to
switch 40 and/or switch 76, the energization circuit of
winding 33 is then transferred to the circuit made up of
and switch 62. Winding 54 has an impedance
gether so a circuit exists either between contact 63 and
member 65 or between contact 64- and member 65 de
value which would not maintain the energization of relay
32. When winding 54 is energized, switch 55 opens so
pending on whether relay so is energized or de-energized,
that even though the abnormal condition or overload
switch 4-5.) subsequently closes, the current level in wind
A shunt circuit made up of a series con
large enough to reduce the current in this circuit to a
ing 33 cannot be increased through the previously men
nection of switch 55, overload switch 40 and high pres
sure switch '76 is connected between terminal 81 and 10 tioned shunt circuit to bring about energization of relay
32. Not-or compressor 22 then remains de-energized un
conductor 82 and can be traced by the following circuit:
til the homeowner or occupant of space 10 discovers the
from terminal 81, switch 55, terminal 41, terminal 42,
non-operating condition of the refrigerating apparatus.
terminal 73, terminal 7% and back to conductor 82.
To reset the system and resore the shunt circuit so wind~
The energization circuit for valve 30 is traced as fol
ing 33 can receive enough current to energize relay 32,
lows: from source of power 45 through conductor '74,
switch 112 must be closed to operate switch 62. Upon
a conductor 83, switch 84, valve 30, conductor 35, and
the energization of relay 6%, member 65 as shown in
terminal 81. Valve 301 is of a conventional solenoid
FIGURE 1 moves from contact 64 to contact 63; how
type to provide an open passage in pipe 25 to allow
ever, during this operation, the wide gap or momentarily
refrigerant to flow to coil 11 whenever the valve is en—
open switch 62 breaks the energization circuit for wind
ing 54 of relay 53 to close switch 55. Winding 33 is then
The space or room thermostat 90 has a bimetal op
energized through the shunt circuit made up of switch
erated switch 91. The switch 91 is connected to control
55 and switches 49 and '76, and the level of current
the energization of relay 92 by a circuit traced as fol
through the winding is sufficient to energize relay 32 to
lows: from a secondary winding 93 of a transformer 94,
a conductor Q5, bimetal 1% and contact 1®1 which
forms switch 91, conductor 162, an energization wind
ing 103 of relay 92, conductor 1%, and back to- the
source of power through conductor 165. Upon clos
ing switch 91, energization winding 103 energizes the
relay to close switch 84 so valve 30 is energized and
coil 11 is cooled to initiate the delivery of cold air to
space 10. Relay 60 can be energized through a circuit
traced as follows: ‘from secondary 93, conductor 195,
conductor 110, winding 61, a conductor 111, a reset switch
112 located remotely from the refrigeration apparatus
re-establish normal operation of the refrigeration appa
ratus. The resetting operation can be accomplished by
opening switch 112 if it had been closed as long as switch
62 momentarily opens the energization circuit for wind
ing 54.
In air conditioning apparatuses of this type which are
used in domestic dwellings as well as other applications,
the safety of the homeowners often depends on the proper
operation of the apparatus; therefore, for the home
owners protection, apparatuses of this type must pass the
Underwriter’s Laboratory requirements. One of the pro
visions of the Underwriter’s Laboratories which applies
21 such as in thermostat 90, a conductor 113, conductor
to reset circuits of this type requires that the system can
95, and back to the source of power. When switch 112
not be placed in an unsafe condition when the circuit
is closed or opened, relay 60 is energized or de-energized,
used to provide the resetting action is either shorted or
respectively, to- momentarily break switch 62 which is
Where low voltage wiring is used and the wires
connected in the energization circuit of relay 53.
are not protected from mechanical damage, a shorting or
Referring to FIGURE 2, the control circuit for the
breaking of the wires could possibly exist. To protect
refrigeration apparatus is shown in a more simpli?ed
the homeowner from any condition whatever it might
manner. The circuit is readily recognized to be quite
similar to the “high impedance” control circuit described
in some detail in the Mobarry Patent 2,898,746.
“high impedance” circuit which is commonly known in
the air conditioning ?eld makes use of two relay wind
ings connected in series. When a shunt circuit is re
moved from one of the relay windings and the two are
connected in series, the current is cut down below the
current needed to maintain the energization of the other
or main control relay. Before the main control relay
and the refrigeration apparatus can be placed back in
operation, the circuit of the impedance relay must be
broken and a shunt circuit re-established around the “high
impedance” relay. Referring to FIGURE 2, winding 54
is the “high impedance” winding. Upon the energiza
tion of the circuit by the closing of the low pressure switch
70, the control relay or contactor 33 is energized to bring
about the energization of motor compressor 22 as shown
in FIGURE 1. The energization of winding 33 is accom
plished through a circuit comprising the normally closed
switch 55 and the overload switch 40 and high pressure
limit switch 76. Upon a call for cooling the space ther
mostat, switch 84 is closed to energize valve 30 which
would cause an increase in the pressure of the suction line
23 to cause switch 70 to close to energize relay 33 as
previously mentioned. As long as no abnormal condi
be which would bring about a short or open in the re
setting circuit, Underwriter’s Laboratory requires that the
safety of the circuit should not be in any way impaired
by the presence of a short or open in the circuit connected
to the remote reset switch 112.
By the use of the momentarily open or wide gap switch
62, the resetting operation for the “high impedance” reset
circuit is obtained from a remote switch.
By means of
the momentarily open switch 62, under no condition can
the circuit be held open to take the impedance relay wind
ing 54 completely out of the circuit so that it can no
longer provide the low current path for winding 33. If
the wires leading to switch 112 are broken or if the switch
112 is jammed shut by the occupant, switch 62 would be
closed, and upon the presence of an abnormal condition
to open switch 4d, the system or refrigeration apparatus
21 would become inoperative and a serviceman would
have to be called before cooling could be obtained.
The importance of the momentarily open switch 62
which can be controlled from a remote position con
tributes to a safety circuit for a refrigeration apparatus
using the “pump-down” method of operation which could
not be otherwise used since a normal resetting system
where the sytem is reset by momentarily opening thermo
stat switch 91 as shown in the Mobarry patent is not
tions come about, the motor compressor 22 will con 70
While the present invention has been described as ap
tinue to cycle to maintain the suction pressure at a level
plying to one particular system, the scope of the present
selected by switch 70, and as cooling is required in
invention is intended to be limited by the following claims
in which I claim:
space 10, valve 30 will be opened when the thermostat
1. In an air conditioning control system, an evaporator
calls for cooling and switch 84 is closed.
Upon the presence of an abnormal condition to open 75 coil mounted in an air stream for delivering cooled air to
a space, a remote motor compressor unit, valve means
ond series circuit providing a lower impedance energiza
tion circuit for said ?rst relay means to energize said ?rst
relay means whereby upon said abnormal switch means
opening said second series circuit said second relay is
energized to maintain said ?rst relay means inoperative
even though said abnormal switch means subsequently
closes until said ?rst switch means is momentarily opened
having an energization winding, means including said
valve means connecting said compressor to said evapo
rator to form a refrigeration system to cool said evapo
rator when said valve is energized, a low pressure re
sponsive switch means connected to said refrigeration
system to be responsive to suction pressure of the com
pressor, switch means providing an open circuit when
to close said normally closed switch.
said suction pressure is reduced to said predetermined
3. A control circuit for an electric motor comprising, a
low value, a source of power, a current overload switch 10 source of power, ?rst relay means having a ?rst energiz
means for providing an open circuit when an excessive
ing winding, said ?rst relay means controlling the oper
current ?ows through a current responsive circuit, a con
ation of said motor, second relay means having a second
trol relay having an energization winding and being
energization winding and a normally closed switch, abnor
mal operating condition responsive switch means provid
adapted to connect said motor compressor to said source
of power through said responsive circuit, a ?rst relay hav 15 ing an open circuit as long as an abnormal operating con
ing an energization winding and arnormally closed switch,
dition exists, second switch means for providing a momen
tary open circuit and a normally closed circuit upon each
a remotely controlled reset relay having a normally
closed switch and a normally open switch, said relay in
operation, circuit means connecting said ?rst energization
winding, said second energization and said second switch
suring a closed circuit when said reset relay is either en
ergized or de-energized, circuit means connecting said
switch of said pressure control, said control relay ener
means in a series circuit to said source of power, said
series circuit having a current below the normal operating
gization winding, said ?rst relay energization winding and
current of said ?rst relay means, circuit means connecting
a parallel connection of said reset switches in series to
said normally closed switch means and said abnormal con
said source of power, space temperature responsive switch
dition responsive switch means in a shunt circuit in par
means, means including said space switch means for con 25 allel with said second relay means and said second switch
necting said valve energization winding to said source of
means whereby a lower resistance path is provided to in
power where upon a call ?or cooling in said space said
crease the current in said ?rst relay means to said normal
valve is energized and said evaporator is cooled by said
operating current, said series circuit being connected in
refrigeration system, abnormal refrigeration operating
said circuit and energized when said shunt circuit is
condition switch means having an open circuit when
broken upon the presence of an abnormal condition and
an abnormal condition is present, circuit means connect
upon said second switch means being operated to momen
ing said condition switch means and said ?rst relay
switch in a series connection in parallel with said ?rst
tarily open said series circuit after said abnormal switch
means closes said low resistance circuit is again estab
relay energization winding and said parallel connection
lished to ‘bring about energization of said ?rst relay means
of said reset switches, said reset relay switches having a 35 and operation of said motor.
wide operating gap such that said closed switch opens
4. A control circuit for an electric motor comprising,
before said open switch closes upon energization or de
a source of power, ?rst relay means having a ?rst ener
energization of said reset relay, said reset relay providing
gizing winding, said ?rst relay means controlling the oper
for normal operation of said control system upon an ab
normal condition occurring to open said abnormal con
dition switch means after said ?rst relay has become ener
ation of said motor, second relay means having a second
energization winding and a normally closed switch, ab
normal operating condition responsive switch means prov
gized and said abnormal condition has disappeared to
ing an open circuit as long as an abnormal operating con
dition exists, second switch means for providing a mo
close said abnormal condition switch means.
2. A control circuit for controlling the operation of an
mentary open circuit when a switch actuator is operated,
electric motor driving a refrigeration compressor in an
air conditioning installation, a source of power, ?rst relay
means having a ?rst energization winding, means connect
circuit means connecting said ?rst energization winding,
said second energization and said second switch means in
a series circuit to said source of power, said series circuit
having a current below the normal operating current of
said ?rst relay means, circuit means connecting said nor
ing said relay means to control said motor, second relay
means having a ‘second energization winding and a nor
mally closed switch, ?rst switch means comprising a nor 50 mally closed switch means and ‘said abnormal condition
mally‘open and a normally closed set of contacts con
responsive switch means in a shunt circuit in parallel
nected in a parallel circuit, said sets of contacts being of
with said second relay means and said second switch
the wide gap type so that upon operation of said switch
means whereby a lower resistance path is provided to
means said parallel circuit is ?rst momentarily open and
increase the current in said ?rst relay means to said nor
then insuring that said parallel circuit has one set of con
mal operating current, said series circuit being energized
tacts normally closed, circuit means connecting said ?rst
when said shunt circuit is broken upon the presence of an
energization winding, said second energization winding,
abnormal condition and upon said second ‘switch means
and said ?rst switch means in series to said source of
being operated after said abnormal switch means closes
power, said ?rst and second windings having impedances
which limit the current in said circuit below a level re
said low resistance circuit is again established to bring
60 about operation of said motor.
quired to maintain 'said ?rst relay energized, abnormal
operating condition responsive switch means, providing
an open circuit when an abnormal operating condition
exists in the operation of said air conditioning installation,
References Cited in the ?le of this patent
circuit means connecting said normally closed switch 65
Winter ______________ __ June 23,‘ 1959
means and said condition responsive switch means in a
Mobarry ____________ .._ Aug. 11, 1959'
Algren _______________ __ May 30, 1961
Myck _______________ -_ Feb. 27, 1962
second series circuit in parallel with a series circuit of
Said second winding and said ?rst switch means, said sec
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