US3190079A - Heat pumps - Google Patents

Description

June 22, 1965 R. F. LAUER Y 3,190,079

' HEAT Puurs 2 Sheets-Sheet 1 Filed Sept. 18,

-RESTRITDR VALVEl .GAPILLARY TUBE R. F. LAUER HEAT PUMPS June 22, 196,5

2 Sheets-Sheet 2 Filed Sept. 18, 1963 United StatesPatent Office 3,190,079 HEAT PUMPS Y Rodney F. Lauer, Staunton, Va., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 18, 1963, Ser. No. 309,677 6 Claims. (Cl. `62`'155) This invention relates to heat pumps that are used for cooling or heating indoor air. Y 1

A heat pump used for cooling or heating indoor air usually includes a refrigerant compressor that is connected through a refrigerant reversal valve to indoor and outdoor heat exchange coils. When indoor air heating is required, the reversal valve is adjusted to route discharge gas from the compressor into the indoor coil operating as a condenser, from which refrigerant liquid is Vsupplied through expansion means into the outdoor coil operating as an evaporator. When indoor air cooling is required,

the reversal valve is adjusted to route the discharge gas from the compressor into the outdoor coil operating as a condenser, from which refrigerant liquid is supplied through expansion means into the indoor .coil operating as an evaporator.

Whenrthe reversal valve of-such a heat pump is adjusted from one positionA to the other, at the instant of reversal, the compressor suction is applied to the high pressure coil that has been operating as a condenser, and the high pressure refrigerant from the latter discharges through the compressor into the low pressure coil that has been operating as an evaporator. This creates undesired noise, may damage the valves'of the compressor,

and liquid from the high pressure coil passes into the compressor, diluting its lubricant, and causing increased wear of the compressor components. Y

In a Widely used heat pump, a heat thermostat, when it calls for indoor air heating, starts the compressor, and energizes arsolenoid `which adjusts the reversal valve of the heatpump to its air heating position. When the heat `thermostat is satisfied, it deenergizes the solenoid of the reversal valve which then adjusts the reversal valve to its indoor air cooling position. A cool thermostat cycles the compressor during air cooling operation.

When such a heat pump is operating to heat indoor air with its outdoor coil operating as an evaporator, low outdoor temperatures may cause frost to form on the outdoor coil, and to melt such frost, 'it is the practice to use a pressurestat responsive to air pressure drop through the outdoor coil caused by the frost, to adjust the reversal valve to its indoor air cooling position so as to operate the outdoor coil as a condenser for melting the frost. Then, when the frost has melted, a control responsive to the rise in refrigerant pressure within the outdoor coil caused by the melting of the frost, adjusts the reversal valve back to its indoor air heating position. Y

` Thus, in such a heat pump, a reversal valve is adjusted to reverse the flow of` refrigerant each time the heat thermostat cycles, and lwhen defrosting of the outdoor coil is started and stopped. t

This invention prevents theV refrigerant from a high pressure coil from flowing through the compressor into Y a low pressure coil when the flow of refrigerant is reversed, by placing a by-pass across the refrigerant expansion means betweenY the coils, and opening this bypass' just before reversal takes place, so that 'when the reversal does take place, the refrigerant from the high pressure coil ows through the by-pass into the low pressure coil instead of through the compressor into the 1W pressure coil.` t

bject of this invention is to preventV refrigerant FIG. 1b is a diagrammatic view of a `defrost relay FIG. lc is aV diagrammatic view of one of the motor starters;

FIG. ld is a diagrammatic view of another motor starter;

FIG. le is a diagrammatic view of a fan relay used; Y IgG. 1f is a diagrammatic view of a by-pass valve relay use FIG. 1g is a diagrammatic view of another time delay relay used;

FIG. lh is a diagrammatic view of still another time delay used,` and FIG. 2 is the electrical control circuit of the heat pump.

The discharge side of a conventional, hermetic, refrigerant compressor C, driven by an electric motor CM, is connected by discharge tube 10 to a conventional reversal valve RV which is connected by tube 11 to outdoor coil 12, and by tube 13 to indoor coil 14. The coils 12 and 14 are connected by capillary tube 16 serving as a twoway expansion means, connected in series with a restrictor valve 17 used for reducing the refrigerantY volume during air heating operation as disclosed in the G. L. Biehn Patent No. 2,785,540. A by-pass tube 19 is connected to the coils 12 and, 14 across the series connection of the valve 17 and the capillary tube 16, and contains a normally g from a` high pressure coil throughA a vnormally closed switch DRSS of the defrost relay DR closed by-pass valve BPV. The reversal valveV RV is connected by suction gas tube 22 to the suction side of the compressor C, through the motor CM as is usualV in hermetic compressors.

The reversal valve RV is connected at its ends through capillary tubes 23 and 24 to a pilot valve 25 which is connected by capillary tube 26 to the discharge gas tube 10. The pilot valve 25 is adjusted by a solenoid RVSOL to route discharge gas to one side of or the other side of. a piston which is not shown, for moving the piston in opposite directions for adjusting the valve RV to'indoor air cooling or indoor air heating positions. When the solenoid RVSOL is energized, it adjusts the valveRV to its air heating position, and when the solenoid RVSOL is deenergized, it adjusts the valve RV to its air cooling position. l

A fan OFdriven by an electric motor OFM moves outdoor air through the outdoor coil 12.

The compressor motor CM is connected through parallel connected switches 1MSS and ZMSS of motor starters 1MS and ZMS'respectively, to ,electric supply lines L1 and L2. The fan motor OFM is connected through switch OFRS of outdoor fan relay OFR to the supply lines. The motor starter 1MS.is connected through switch CTSI'of cool thermostat CT to the supply lines. The fan relay OFR is connectedV through series connected switch CTS2 of the cool thermostat CT, and normally closed switch DRSl of defrost relay DR to the supply lines'. The `reversal valve solenoid RVSOL is connected in series with normally open switch 1TDRS1 of thermal time delay means such as relay lTDR to the supply lines. The motor starter V2MS is connected in series with parallel connected switches 1TDRS2 of the relay lTDR and DRS4 of the defrost relay DR to the supply lines.

The relay 1TDR has a heater resistor 30 connected in parallel with by-pass valve relay BPVR Yand in series with Patented June 22, 1965 the supply lines.

Y thereon.

to the supply lines. When the resistor 30' is energized,

time is required for it tov heat and cause its. switches Time delay means such as delay relay ZTDR has an elec- Y tromagnetic winding ZTDRW connected through normally closed switch YBPVRSI of the by-pass valve relayBPVR to the supply lines; has normally closed switchesZTDRSl and ZTDRSS, and has a switch ZTDRSZ which responds f to heat fromheaterV resistor 40, and which warps open when the resistor 40fis heated.Y Ther-resistor 40 is connected through the normally closed switch ZTDRSS to A time delay means such as relay STDR, similar to the` relay VZTDR, has an electromagnetic winding STDRW Vconnected through normally open switch BPVRSZ'of the bypass relay BPVR to the supply lines; has normally open switches 3TDRS1 and BTDRS, vand `has a` normally closed switch'TDRSZ which responds to heat from heater resistor 5t), and which warps openV when the resistor 56 is deenergized and has cooled. The

lTDR, and the by-pass valve relay BPVR through the z normally closed switch DRSSVof the defrost relay DR. The' relaykBPVR opens its switch BPVRSI and ycloses itsV switch BPVRSZ. `The-now open switch BPVRSI dei energizes the winding ZTDRW of the time delay relay ZTDR which opens itsswitches ZTDRSI and 2TDRS3, the

latter deenergizing the heaterresistor 40 which cools and permits the switch ZTDRSZVto warp closed. Thel switch ZTDRSZ is not usedat this time, and isused'when the thermostat HT`is` satisfied as'will be describedlater. The now closedv switchfBPVRSZ energize'sthe Iwinding STDRW of the time delay relay STDR whichV closes its switchesSTDRSl and-.3TDRS3. The now closed switch v3TDRS1 energizes the YbypassV valve solenoid BPVSOL through the closed switch .'foTDRSZ` of the time delay relay ISTDR." The solenoid BPVSOL opens the by-pass valve BPV, permitting high pressure gas from the outdoorcol Y 12 which has been Voperating as a-condenser, to ow ,through the by-pass tube'19 into the indoorc'oil 14 which has been operating as an evapator. The now closed switch Y STDRSS energizes the heatenresistor 50- of therelay l STDR, which heats and after a period of time, causes resistor 501is connected through the switch 3TDRYS3 to the supply lines. Y

The by-pass valve solenoid BPVSOL is connected Vthrough series connected switches ZTDRSI and ZTDRSZ to the supply lines, and is also ,connected` through series connected switches 3TDRS1' and STDRSZ to the supply f lines. I Y

The defrost relay DR is connected in series with normally closedswitch DLCS `of the defrost limit control-DLC,

r and parallelV connectedswitches 'DCS of defrost control` DC, and DRSZ of the defrost relay DR.

The defrost control DCV `is a conventional defrost initiating control which responds to air pressure dropY f across the outdoor coil V12 caused by formation'offrost The defrost limit control DLC is aconventional controlY which responds to refrigerant pressure within the outdoor coil 12.V `V f Air cooling operation v When air cooling is required,'the heat thermostat HT is olf, and the reversal valve RV Yis in its air cooling position. The cool thermostat CT closes its switches'kCTSI and CTS2. The closed switch CTvSl energizesrthe motor starter 1MS which closes its switch IMSS whichstarts the compressor motor CM. The closed switch CTSZ 'enthe switch STDRSZ to warp open andtoV deenergizethe solenoid BPVSOL' which V'closes the 'by-pass valve BPV:V

After a period of time sucientfor the by-pass valve BPV to have opened and closed as described, the'switches ITDRSI and ITDRSZ of th'etime'delay relay lTDRare warped closed by heat` from their energized .heater resistor 30. The now closed switch lTDRSl-energizesthe reversal valve solenoid RVSOL which adjuststhereversal valve RV to its `air heating position. At the same time, thenow closed switch ITDRSZ energizes the motor starter ZMS which closes its switch ZMSS, starting lthe-compressor motor CM. Discharge gas'from the compressor C flows through the discharge gas tube r10, the reversal valve RV and the tube 13 into the indoor coil 14 operating as Y a condenser. Liquid from the coil 14 ows through :the

' capillary tubel''and theV restrictor valve 17 into the outcompressor C.

ergizes the fan relay OFR throughthe normally closed i switch DRS1 of ythe defrost relay DR. The energized relay OFR closes its switch OFRS, starting the fan motor OFM. At this time, the by-passvvalve' solenoid BPVSOL is deenergized, and the by-passvalve BPVis closed. Discharge gas flows from the compressor C through the discharge gas tube 10, the reversal valve RV and the ktube k11V into the outdoor coil 12'operating as aV condenser. Liquid from the coil 12 flows through the capillary` tube 16 andVK i the restrictor valve 17 into the indoor coil'lfiV operating as GasV from the fcoil 14 ows through the an evaporator. tube 13, the reversal valve RV Yand the suction tube 22 to the suction side of the compressor CA. The cool therdoor coil 12 operating as yan evaporator. GasV from the A coil 12 flows'through the ktube 11,1the reversal valve RV and the suction gas tube'22 to the suction sideof the When the heat thermostat HT ssatisfied, it opensits switches HTSlYa'nd HT S2.V VThe now openswitch'HTSl denergizes the fan relay OFRf'fwhich opens its switch `OFRS,'-stopping the fanfmotor OFM. The now open vswitch HTSZ deenergiz'esthe heater resistor 30'of the` time Vdelay' relay lTDR, andfthe by-passfvalve relay BPVR. Therelay BPVR opensy its switch BPVRSZV and The `now open switch BPVRSZ deenergizes the 'winding -ZFDDRW of the time de# lay relay raTDR which'opensl its switches 3TDRS1- and the heater V.resistor 59 which cools and causes the switch,

mostat CT cycles the compressor'motor CM andthe Y outdoor fan motor OFM.

There would be one or more indoor air fansV associated with the indoor coil 14, butsince their operationis not affected by this invention, they are Vnot'shown.

Air heating operation' When indoorv air heating'is required, YVthe cool thermostat CT is'7 of course, off. When the heat thermostat i vI-IT calls forheat, it'jcloses its switches HTS1 and- HTSZ.

The closed switch HTSl energizesV thefan `relay OFR through-the normally closed switch DRSl of the defrost Y relay VDR. The relay OFR elosesits'switchl OFRS starting the fan motor OEM. Therclosed switch HTSZ `energizes the heater resistor 30 of the timedelayrelay noid BPVSOL which closes the byV-passfvalveifBl Venergized through .the closedlswit-chST-DRSZ.' The now ergizes the lwindir1g`2fl`DRW of the'time delay relay ZTDR Y now closed switch ZTDRSI of the time delay relay ZTDR f the by-pass valve BPV, permitting Vhigh pressure gas y from the indoor coil 14.which has been operating'as a"V condenser, to ilow through the by-passv tube` Y19-into ,the outdoor coil 12k which has been operating as an evapo i BPV to have opened andv closed as described,tireV V1TDRS1 and lTDRSrzassoci'ated withgthenow STDRSS. .The now open switch 3TDRS3 deenerg-izes STDRSZ nto warp closed, but since the switch '3TDRS1 is now open, the byapass lvalve solenoid BPVSOL cannot be closed switch BPVRS'I of theiby-pass valve relayBPVR enwhich closes its switches `ZTDRSI and2TDRS3. The

energizes the by-passV valve solenoid BPVSOL'throughf the closed switch ZTDRSZ. The solenoid BPVSOL opens q' ator. YThe now Yclosed ,switch ZTDRSS energizes nthe heater resistor 40 of the relayZTDR'. The resistor-t0 heats suiciently after a period offtime to c :a'usetheL switch 2TDRS2` to Vwarp open and Vdeenergizefthe After a period of time sutiicie'ntY forthe by-pass Ya gized heaterresistor 30 of the timedelay relay ITDR motor CM.

Defrostng operation Defrosting is required only during air heating operation'when the outdoor coil 12 is operating as an evaporator. When suiicient frost has formed on the outdoor coil 12 to require the latter to be defrosted, the increased air pressure drop across the coil 12 causes the switch DCS of the defrost control DC close; At this time,

" the refrigerant pressure within the coil Y12 is relatively low, and the -switch DLCS ofthe defrost limit control DLC is closed; Ilhe defrost relay DRis energized L through ,the closed switches DCS and DLCS, `and opens its switches DRS1 and DRS3, and closes its switches DRS2' and DRS4. The opening of the switch DRSlrdeenergizes the fan relay OFR which opens its switch OFRS, stopping the outdoor fan motor OFM. Since there is now no air being blown over the coil 12, the

The now defrost4 control DCS opens, but the now closed switchL `DRSZ connected across the switch DCS maintains the relay DR energized. The now open switch DRS3 de-` energizes the heater resistor 30 ofthe time delay relay 1TDR, and the by-pass valve relay BPVR. The now deenergized relay BPVR opens its switch BPVRSZandcloses its switch BPVRSl. The now open switch BPVRS2 deenergizes the winding STDRW which opens its switches 3TDRS1 and 3TDRS3. The now open switch 3TDRS3 deenergizes the heater resistor 50 which cools and causes theswitch 3TDRS2 to warp closed, butsince the switch 3TDRS1 is now open, the by-pass valve solenoid BPVSOL cannot be energized through the closed switch 3TDRS2.V

The now closed switch BPVRSI energizes the winding ZTDRW which closes its switches ZTDRSI and 2TDRS3. The now closed switch 2TDRS1 energizes through the closed switchv 2TDRS2 the by-pass valve a solenoid BPVSOL which opens vthe by-pass valve BPV, permitting high pressure gas 'om the indoor coil 14 which has been operating as a condenser to iiow through the bypass tube 19 into the outdoor coil 12 which has been operating as an evaporator. The now closed switch 2TDRS3 energizes the heater resistor 40 which heats, and after a period of time, causes the svrntch 2TDRS2 to warp open and deenergize the solenoid BPVSOL which closes the by-pass valve BPV.

After a period of time sufficient for the by-pass valve BPV to have opened and closed as described, the switches 1TDRS1 and 1TDRS2 of the time delay relay ITDR warp open as a result of the heater resistor 30 having been deenergized. The now open switch 1TDRS1 deenergizes the reversal valve solenoid RVSOL which adjusts the valve RV to its air cooling position. The now open switch 1TDRS1 cannot deenergize the motor starter 2MS since it is shunted by the closed switch DRS4 so that the compressor motor CM remains energized.

The outdoor coil 12 now operates as a condenser, and the heat from it melts the frost that has formed on it. When the frost on the coil 12 has melted, the pressure within the coil12 rises and opens the switch DLCS of the defrost limit control DLC, deenergizing the defrost relay DR which opens its -switches DRS2 and DRS4 and closes its switches DRS1 and DRS3. 'Ihe now closed switch DRS1 energizes the fan relay OFR which closes its switch OFRS, starting the fan motor OFM. The now closed switch DRS3 energizes the heater resistor 30, and the relay BPVR. The latter closes its switch BPVRS2 and opens its switch BPVRSI. The now open switch BPVRSI deenergizes the winding ZTDRW which opens its switches 2TDRS1 and 2TDRS3, the latter deenergizing the heater resistor 40 which cools and permits the switch 2TDRS2 to warp closed; 'I'he now closed switch .under control of the heat thermostat HT. v

BPVRS2 energizes the winding STDRW which closes its switches 3TDRS1 and 3'IDRS3.Y The now closed switch 3TDRS1 energizes Vthe by-pass valve solenoid BPVSOLrthrough the closed switch 3TDRS2. The solenoid BPVSOL opens the by-pass valve BPV, permitting high pressure gas from the outdoor coil 12 which has been operating as a condenser, to `ilow through the bypass tube 1,9Yinto the indoor coil 14 which has been operating as an evaporator. The now closed switch 3TDRS3 energizes the heater resistor 50 which heats and after a period of time causes the switch, 3TDRS2 Vto warp. open and to` deenergize the solenoid BPVSOL whichvcloses the by-pass valve BPV. a Y

After a period of Ytime sucient for theVby-pass [Valve BPV Yto have opened and then reclosed as described, the switches 1TDRS1 and 1TDRS2 are w-anped yclosed by heat j from the now energized heater resistor 30. The now closed switch 1TDRS1 energizes the reversaly valve solenoid which acts to adjust the reversal valve RV to its air heating position. AtrtheV `same time, the closedV switch -1TDRS2 energizes the motorst'arter` 2MS which Was deenergized by the opening of the switch DRS4. The heat pump `is now back in indoor air heating operation Thedefrost relay could be of the slow switch opening type so that the switch DRS4 would remain closed until the switch 1TDRS2 closes, thus maintaining the `com-- pressor in operation during the changeV over from defrost` ing to indoor air heating operation.

It is seenthat this invention provides that just before the reversal valve is lreversed in either direction, aby-pass is opened for permitting high pressure gas` from the coil Which has lbeen operating as -a condenser to il-ow directly into the coil which hasbeen operating as an evaporator, following lwhich -the by-pass is closed, and the reversal valve is reversed. j

`What is claimed is: Y Y. u

1. A heat pump comprising an indoor air coil, an outdoor air coil, a Vrefrigerant compressor,4 reversal valve means and two-way dexpansion means connected in a closed refrigeration circuit, means including a lirst solenoid for adjusting said valve means to route refrigerant from said compressor to said outdoor coil to operate said outdoor coil as a condenser and said indoor coil `as an evaporator, and for adjusting said valve means to route refrigerant from said compressor to said indoor coil to operate said indoor coil as a condenser and said outdoor coilas an evaporator, said valve means being. adjusted to route Vrefrigerant from said compressor to said outdoor coil when said solenoid is energized, and to route refrigerant from said compressor to said indoor coil when said solenoid is deenergized, a by-pass tube connecting said coils, a normally closed valve in said tube, a normally energized, second solenoid for opening said normally closed valve when said second solenoid is energized, a defrost relay having a normally `closed switch, a defrost initiating control having a switch which closes when frost forms on said outdoor coil when said outdoor coil is operating as an evaporator, means including said switch of said control, when closed, in series with said defrost relay for energizing said defrost relay, a heat control thermostat having a switch which closes when said lthermostat calls for heat, and means including means energized when said thermostat switch and said switch ofsaid deost relay are closed, for first energizing said second solenoid, for next deenergizing said second solenoid, and -for next energizing said first solenoid.

2. A heat pump as claimed in claim 1 in which means including means energized when said thermostat switch opens, andrwhen said switch of said'defrostrrelay opens, is provided for lirst energizing said second solenoid, for next deenergizing said second solenoid, and for next deenergizing said rst solenoid.V

3. A heat pump as claimed in claim 2 in which a defrost terminating control is provided and which has a normally closed switch which opens when frost has melted .from said outdoor coil,"aind in which saidv lastmentioned switch is in series with said switch of said defrost initiating control and said defrost relay. ,Y

4. Aheatpump as claimed in lclaim 1 in whichaY defrost i "said second timing meansris energized and then reopens terminating control is provided andwhichv has anormally' closed switch which opens when frost has melted from said outdoor coil, and 1in which said last vmentionedY Vswitch is in series with said switch of said defrost initiating c ontrolv and said defrost relay. Y

5. A heat pump comprising ',an'indoor aircoil, an outdoor air coil, a refrigerant, compressorandtwo-way expansion means connected in a closed refrigerationY circuit,

means including Va ,rst solenoid for adjusting said valve 'to' a krst position when 4said solenoidV is '.en'erg'ized, -and adjusting said valveimeans to a second iposition when Vsaid solenoid is deenegized, said valve means in said,k d Irst position routing refrigerant from'said compressor toV saidk outdoor coil to operate 'said outdoor coilas a ,con-V denser and said indoor coil as anv evaporator, saidjvalve means'jin said second position routing refrigerant'A from said compressor to said indoor coil-to operate said indoor Y coil as a condenser. and said outdoor coil as'an evaporator,

a 'by-pass tube connecting said coils, a normally` closed valve in. said tube, a normally deenergizerLsecond solenoid for opening said normally closed valve whenVV said ,Y Y g, d Y g A Y,

Y. frost terminating control is provided ,and which hasV ar normally closed-switch opens whenY frosrtthas melted,

second solenoid is energized, ad'defrrost initiating control having` a switchk whichv closes whenfrost forms on said Youtdoor coil when said outdoor coil is operating as anVr fevaporator, means including said switchfof said control in series with said defrostrelay for energizing said defrost relay when said switch of said control isclosed, aheat 1 control thermostatlhaving*alswitch which closes when ,Y

, said thermostat calls for heat, a by-pass valve relay having a rst switch which is closed and .3 second switch which is open when said by-pass valve relay isedeene'rgized, rst

period of time after said timing means is deener'gized,

. means including said thermostat switch, lwhen closed, and

V'is energized and then reopens. after a predetermiuedj Y Y timing means forY energizing said first solenoid aftersaidA second solenoid has been energized and deenergi'zed,-`

' relay Vfor energizing saiddseconditiming means, means int cludingV said, switch `,of -said second timing means for `after apredetermined periodrof time, third timing means havinga switch which closes when said third timing means period of time, rneans including said open switchg'when closed, of saidl 'by-pass, valve Yrelay for-energizing said third tirningrnieans, means including said switch'of s aid t third'ltiming means' for energizing and deenergizing said second solenoid, rneans including said swit'chof saidrst means including Vsaid closediswvitch of said by-pass valve -,energizing rand deenergizing said second' solenoidsaid ,y firsttiming `means being. deenergized when saidfbyfpass valve relay is deenergized andV closesits normallynclosed switch, said switch of saidfirstrtiming means( opening and l deenergizingsaid first solenoid after said'se'cond solenoid has, been energized., and deenergized ,by the closingdan'd` L openingrespeotively, of said switchnof said'sec'o'nd Vtiming means' t Y Y .y 6. AAhe'at pumpasclaimed in claim 5 in which a defrom said outdoor coil, and in which said lasty mentioned 2,143,687 1/39Y Crago v 62-150-,X` 2,801,524` v8/57 t lFinetti V A62-1564 f 23,103,793 Y 9/63Y Kyle et al, -22 62-'160 3,103,794 9/63-,Ky1eeta1 Y 152-160 3,123,985 Y 3/,641 Burt' y ;62-1'60 Vswitch is in series with said switchof said initiating control j and Ysaiddefrost relay. Y

References Citedy by the Examiner UNITED STATES PATIENTSk ROBERTY OLEARY, Primary Examiner.

Claims (1)

1. A HEAT PUMP COMPRISING AN INDOOR AIR COIL, AN OUTDOOR AIR COIL, A REFRIGERANT COMPRESSOR, REVERSAL VALVE MEANS AND TWO-WAY EXPANSION MEANS CONNECTED IN A CLOSED REFRIGERATION CIRCUIT, MEANS INCLUDING A FIRST SOLENOID FOR ADJUSTING SAID VALVE MEANS TO ROUTE REFRIGERANT FROM SAID COMPRESSOR TO SAID OUTDOOR COIL TO OPERATE SAID OUTDOOR COIL AS A CONDENSER AND SAID INDOOR COIL AS AN EVAPORATOR, AND FOR ADJUSTING SAID VALVE MEANS TO ROUTE REFRIGERANT FROM SAID COMPRESSOR TO SAID INDOOR COIL TO OPERATE SAID INDOOR COIL AS A CONDENSER AND SAID OUTDOOR COIL AS AN EVAPORATOR, SAID VALVE MEANS BEING ADJUSTED TO ROUTE REFRIGERANT FROM SAID COMPRESSOR TO SAID OUTDOOR COIL WHEN SAID SOLENOID IS ENERGIZED, AND TO ROUTE REFRIGERANT FROM SAID COMPRESSOR TO SAID INDOOR COIL WHEN SAID SOLENOID IS DEENERGIZED, A BY-PASS TUBE CONNECTING SAID COILS, A NORMALLY CLOSED VALVE IN SAID TUBE, A NORMALLY ENERGIZED, SECOND SOLENOID FOR OPENING SAID NORMALLY CLOSED VALVE WHEN SAID SECOND SOLENOID IS ENERGIZED, A DEFROST RELAY HAVING A NORMALLY CLOSED SWITCH, A DEFROST INITIATING CONTROL HAVING A SWITCH WHICH CLOSES WHEN FROST

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