JPH0426834Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to an air conditioner having a defrosting operation function.

(Prior Art) As a specific example of defrosting operation in an air conditioner, there is, for example, a device described in Japanese Patent Application Laid-open No. 190660/1983. This equipment is equipped with a variable frequency compressor, and during defrosting operation, the compressor is driven at a high frequency, that is, with a greater defrosting capacity, thereby shortening the defrosting time and improving the defrosting operation. When the heating operation is restarted after the end of the heating operation, the temperature is shifted from the high frequency to a frequency that matches the indoor air conditioning load, thereby improving the immediate heating performance when the heating is restarted.

By the way, switching between the heating operation and the defrosting operation as described above is performed based on the temperature detected by a frost amount detection sensor attached to the outdoor heat exchanger, for example, an outdoor heat exchanger temperature detection sensor. . In other words, when the detected temperature falls below a predetermined reference temperature, it is determined that there is a large amount of frost and automatically switches to defrosting operation. However, if the defrosting operation is immediately switched based only on the signal from the temperature detection sensor described above, depending on the operating conditions such as low outside temperature and high humidity,
Defrosting operations are frequently repeated, and sufficient heating operation time is not secured, which may result in a significant loss of user experience and air conditioning comfort.

Conventionally, for example, when starting heating operation or restarting heating operation after defrosting operation, a heating priority period was set in which heating operation was continued for a certain period of time, and during this period, frost formed on the outdoor heat exchanger and Even if the heating capacity is reduced, the system first ensures that the room temperature rises as desired by the user, and then restores the heating performance of the device. In addition, a maximum allowable time is set for the duration of defrosting operation, and even if complete defrosting is not achieved even after this maximum allowable time has elapsed, the system will forcefully return to heating operation. This suppresses the drop in room temperature during frost operation to prevent significant loss of air conditioning comfort.

(Problems to be solved by the invention) However, even in switching control that sets a heating priority period that emphasizes indoor air conditioning comfort or a maximum allowable time for defrosting operation as described above, the following problems still occur. may occur. For example, in cold regions or during heating operations at low outside temperatures and high humidity, the rate of frost formation on the outdoor heat exchanger is unexpectedly fast, and defrosting cannot be performed using the normal maximum allowable time. During operation, unmelted remains may occur, and during subsequent heating operations and defrosting operations that are repeated alternately during the heating priority period and the maximum allowable time, complete defrosting may not be achieved forever, or unmelted portions may remain after each defrosting operation. As the amount increases, the heating capacity may gradually decrease. As a result, heating operation efficiency decreases, and air conditioning comfort gradually becomes unobtainable.

This idea was made in view of the above,
The purpose is to provide an air conditioner that can suitably restore heating operation efficiency without significantly impairing indoor air conditioning comfort.

(Means for solving the problem) Therefore, the air conditioner of this invention performs heating operation by circulating the gas refrigerant discharged from the compressor 1 from the indoor heat exchangers 5 and 6 to the outdoor heat exchanger 2. As shown in FIG. 1, the air conditioner includes frost amount detection means 40 for detecting the amount of frost formed on the outdoor heat exchanger 2.
and frost amount comparison means 72 which issues a defrost start signal when the detected amount of frost exceeds the reference value and issues a defrost end signal when the detected amount reaches the reset value, and the defrost start signal is inputted. an operation control means 60 which switches from the heating operation to the defrosting operation when the defrosting operation is completed, and which terminates the defrosting operation and restarts the heating operation when a defrosting end signal is input; a forced return means 73 that issues a defrosting end signal to the operation control means 60 when the heating operation is resumed;
Heating priority means 71 that prevents input of the defrosting start signal from 2 to the operation control means 60, and counting means 74 that counts the number of defrosting operations.
a forced signal generating means 75 for generating a forced defrosting signal when the defrosting operation completed after the count value exceeds a predetermined value is performed by a defrosting end signal from the forcible return means 73; When the forced defrosting signal is generated, a defrosting start signal is issued after the resumed heating operation continues for a second priority period shorter than the first priority period, and the count value of the counting means 74 is reset. It has a forced defrosting operation switching means 76.

(Function) In the air conditioner configured as described above, the heating operation and the defrosting operation, which are continued for at least the first priority time, are repeated until the number of times of the defrosting operation reaches a predetermined value (for example, 5 times). The subsequent defrosting operation is terminated by the defrosting end signal from the forced return means 73, and if there is unmelted frost remaining, the resumed heating operation is restarted from the first priority time. After continuing for a short second priority time, forced defrosting operation is performed. The room temperature is restored by heating operation within this second priority time, and by shortening this time, frost growth is suppressed during this time, and therefore, during the forced defrosting operation, the It becomes possible to defrost. Thereafter, similarly, the heating operation is performed for a predetermined number of times for a period longer than the first priority time to ensure air conditioning comfort for the user, and then the same process as above is performed for the remaining melt.
In this way, when frost remains unmelted, the unit automatically switches to forced defrost operation as appropriate and continues operation while restoring the unit's heating performance, without significantly impairing indoor air conditioning comfort. Therefore, it is possible to improve the heating operation efficiency compared to the conventional method.

(Example) Next, a specific example of the air conditioner of this invention will be described in detail with reference to the drawings.

FIG. 2 shows a refrigerant circuit diagram of an air conditioner according to an embodiment of this invention. In the diagram
indicates an outdoor unit, and A and B indicate indoor units, respectively. Outdoor unit X is composed of a compressor 1, an outdoor heat exchanger 2, an outdoor fan 3, a pressure reducing mechanism 4, etc. B is composed of indoor heat exchangers 5, 6 indoor fans 7, 8, and the like. The compressor 1 is equipped with a drive source 9 using an inverter, and a discharge pipe 10 thereof,
Suction pipe 11 in which the accumulator 13 is interposed
is connected to the four-way switching valve 12. A second gas pipe 14 is connected to one connection port of this four-way switching valve 12.
However, a first gas pipe 15, an outdoor heat exchanger 2, and a liquid pipe 16 are sequentially connected to the other connection port. A pair of second gas branch pipes 1 are connected from the second gas pipe 14.
7 and 18, and a pair of liquid branch pipes 19 and 20 are branched from the liquid pipe 16, respectively, and indoor heat exchangers 5 and 6 are connected between them. The pressure reducing mechanism 4 includes first capillary tubes 21, 22 and first on-off valves 23, 24 in each liquid branch pipe 19, 20.
In addition, a parallel circuit including a second capillary tube 25, a check valve 26, and a second on-off valve 27 is provided in the liquid pipe 16. Note that the check valve 26 is arranged to allow the flow of refrigerant only during cooling. In the figure, 30 and 31 are mufflers, 32 is a gas shutoff valve, 33 is a liquid shutoff valve, and 34 is a dryer filter.

In the above device, the liquid pipe 16 between the outdoor heat exchanger 2 and the dryer filter 34 is further provided.
A bypass pipe 3 in which a defrost on-off valve 36 and a throttle 37 consisting of a capillary tube are interposed
5, it is connected to the discharge pipe 10. Note that the bypass pipe 35 and the discharge pipe 10 are provided with check valves 38 and 39, respectively, near their branch points. In addition, the outdoor heat exchanger 2 is provided with an outdoor heat exchanger temperature detection sensor consisting of a thermistor for detecting the temperature of the heat exchanger 2 in order to automatically switch between heating operation and defrosting operation, which will be described later. (Frost formation amount detection means) 40 is attached.

In the above air conditioner, the four-way switching valve is configured so that the refrigerant circulates in the direction (in the direction of the dashed line arrow in the figure) in which the outdoor heat exchanger 2 functions as a condenser and each of the indoor heat exchangers 5 and 6 functions as an evaporator. 12 to drive the compressor 1, cooling operation is performed. At this time, both the second on-off valve 27 and the defrost on-off valve 36 are closed, and each of the first on-off valves 2
3 and 24 close the stop side and open the drive side. On the other hand, in heating operation, the four-way switching valve 12 is switched from the above, and the refrigerant is directed in the direction (in the direction of the solid line arrow in the figure) in which each of the indoor heat exchangers 5 and 6 functions as a condenser and the outdoor heat exchanger 2 functions as an evaporator. This is done by circulating. At this time, the defrost on-off valve 36 is closed, and the first on-off valves 23 and 24 are both opened. When the two chambers are operated simultaneously, the second on-off valve 27 is closed.
Also, when operating in one room alone, the indoor fan on the stopped side,
For example, stop 8. In this case, the refrigerant flowing through the indoor heat exchanger 6 on the stopped side is not given any heat exchange beyond natural heat radiation, resulting in a gas-liquid mixed state with a large amount of gas components. The first capillary tube 22 acts as a large flow resistance, and therefore the indoor heat exchanger 6 on the stop side
The amount of refrigerant flowing through the refrigerant is limited to a small amount, and most of the refrigerant is circulated through the indoor heat exchanger 5 on the operating side. However, by keeping the stopped side in a state where it can flow as described above, it is possible to prevent liquid from accumulating. During this single room operation, the second on-off valve 2
7 is opened when the operating frequency of the compressor 1 is higher than a preset reference frequency (for example, about 45 Hz), and closed when it is lower than the reference frequency. This is because when the operating capacity of the compressor 1 is low, the amount of refrigerant flowing through the first capillary tube 21 on the operating side is small and sufficient pressure reduction characteristics cannot be obtained, so the second capillary tube 25 further reduces the pressure. This is to maintain an appropriate decompression effect.

Then, the defrosting operation in the above device starts from the heating operation state to the outdoor fan 3 and each indoor fan 7,
8, and at the same time, open the defrost on-off valve 36, which had been closed until then. At this time, the high-temperature gas refrigerant discharged from the compressor 1 is divided into two streams in the discharge pipe 10, as shown in the direction of the dashed-dotted arrow in FIG. The outdoor heat exchanger 2 is defrosted by circulating the refrigerant such that the refrigerant flows into the compressor 1 through the first gas pipe 15 and returns to the compressor 1 from the first gas pipe 15. On the other hand, the other refrigerant separated by the discharge pipe 10 is supplied to each indoor side through the second gas pipe 14. The amount of refrigerant flowing indoors is determined by the flow resistance ratio between the indoor pipe and the bypass pipe 35. For this purpose, the bypass pipe 35 is provided with a throttle 37 whose flow resistance is adjusted as follows. are doing. In other words, by stopping each of the indoor fans 7 and 8, the indoor heat exchangers 5 and 6 are not forced to cool, but their temperature gradually decreases due to natural heat radiation. Therefore, the bypass piping 35 is designed so that the flow rate is such that at least an amount of heat equivalent to this amount of natural heat radiation is given to the indoor heat exchangers 5 and 6 by the circulating refrigerant, and an excessive amount of liquid does not accumulate on the indoor side. The flow resistance of the throttle 37 is adjusted so that the defrosting ability on the side, that is, the flow rate of the refrigerant is ensured. As a result, even during defrosting operation, the indoor heat exchanger 5,
6 can be suppressed, and as a result, the decrease in room temperature is further reduced, and when heating operation is restarted after defrosting operation, the temperature of the indoor heat exchanger is maintained at a high temperature, so that the temperature decreases immediately. It is possible to blow out warm air, providing immediate warmth.

Next, switching control between heating operation and defrosting operation as described above will be explained.

First, FIG. 3 shows a control block diagram of the above-mentioned device, and as shown in the figure, this air conditioner consists of an indoor control device 51 arranged in each indoor unit A and B,
52, and an outdoor control device 53 disposed in the outdoor unit
Reference numerals 1 and 52 each include an operation switch 54, a temperature setting section 55 for setting a desired air conditioning temperature, and a room temperature sensor 56 for detecting the room temperature. Each indoor control device 51, 52 outputs an operation request signal when the operation switch 54 is ON and the temperature detected by the room temperature sensor 56 has not reached the set temperature, and at the same time, the set temperature and the detected temperature. A temperature difference signal is output. On the other hand, the outdoor control device 53 controls each control device such as the first on-off valves 23 and 24 to maintain the heating operation state, and also controls the driving frequency of the compressor 1 based on the operation request signal and the temperature difference signal. An air conditioning operation control section 57 that controls heating operation while varying the temperature, a defrosting operation control section 58 that controls each control device to the defrosting operation state, and output from either of these control sections 57 and 58. An operation signal output section 59 for placing each control device such as the first on-off valves 23 and 24 into an operation state for heating or defrosting according to a signal, and the air conditioning operation control section 5
It has an operation mode selection section (operation control means) 60 for appropriately switching between the heating operation according to 7 and the defrosting operation according to the defrosting operation control section 58.

The air conditioning operation control section 57 determines an inverter frequency based on the operation request signal and the temperature difference signal during heating operation, and drives the compressor 1 at this frequency. In other words, at startup or when indoor thermostat is turned on
In other words, when restarting when a temperature difference occurs again after the room temperature reaches the set temperature and the operation is stopped, and when heating is resumed after the defrosting operation is finished, etc., which will be described later,
The operation is started at the initial setting frequency according to the number of units requested for operation at that time and the temperature difference, and after reaching the set frequency, the
PID control is used to perform frequency control according to changes in air conditioning load. On the other hand, when the heating operation is switched to the defrosting operation, the air conditioning operation control section 57 drives the compressor 1 at a predetermined constant defrosting operation frequency.

The operation mode selection section 60 controls switching between heating operation and defrosting operation in accordance with the defrosting start signal and the defrosting end signal generated by the defrosting signal generating section 61, and controls the switching between the heating operation and the defrosting operation. The signal generating section 61 determines the heating operation time th and the defrosting operation based on the detected temperature signal Te from the external heat exchanger temperature sensor 40 and the output signals from the air conditioning operation control section 57 and the defrosting operation control section 58, respectively. A defrosting start signal and a defrosting end signal are generated based on the measured times from the first and second time measuring sections 62 and 63 that measure the time td. This will be explained based on the control flowchart shown in FIG.

When the operation is started, first, in step S1, a count bit n for determining the number of times of start-up and defrosting operation is initially set to -2, and then, in step S2, heating operation is started. At the same time as this start, measurement of the heating operation elapsed time th is started, and until this th exceeds the first priority time, for example 20 minutes, in step S3, steps S3 and S2 are repeated.
Heating operation continues for at least 20 minutes. In other words, the above step S3 is a processing step that constitutes the heating priority means 71, and thereby, when the heating operation is started and when the heating operation is restarted after the defrosting operation, which will be described later, is completed, regardless of the frost formation state in the outdoor heat exchanger 2. Then, perform operations that prioritize raising the room temperature. After the heating operation has been performed for 20 minutes, the temperature Te detected by the external heat exchanger temperature sensor 40 is compared with the reference temperature Td1 in step S4.
Repeat steps S2 to S4 to continue heating operation and measurement of its operation time. The above Te detects a temperature equivalent to the refrigerant evaporation temperature in the outdoor heat exchanger 2 during heating operation, and if frost forms on the outdoor heat exchanger 2, the heat exchange capacity increases as the amount of frost increases. As a result, the refrigerant evaporation temperature also decreases, resulting in the above-mentioned decrease in Te. Therefore, the heat exchanger temperature at a predetermined amount of frost formation is determined in advance, and this is set as the reference temperature Td1. When the above Te falls below this Td1, it is determined that the amount of frost formation is large, and a defrost start signal is issued. . This step S4
and step S6, which will be described later, constitute a frost amount comparison means 72 that issues defrosting start and end signals based on the detection signal from the external heat exchanger temperature sensor 40.

If it is determined in step S4 that Te is equal to or less than Td1, the heating operation and the measurement of the operating time are interrupted, and the process moves to step S5. Heating operation time measurement value th held at this time
naturally indicates 20 minutes or more. and,
For example, if frost has already formed on the outdoor heat exchanger 2 at the start of the heating operation, Te may fall below Td1 during the heating priority period. At this time, the processing steps proceed from step S3 to S4 and S5, so th remains at 20 minutes.

In step S5, the defrosting operation described above is started. At the same time, measurement of this defrosting operation time td is started, and this defrosting operation is continued from S5 until the conditions of termination determination steps S6 and S7 are satisfied. The step S6 is a step for determining the end of defrosting based on the temperature Te detected by the external heat exchanger temperature sensor 40. By continuing the defrosting operation described above, the high-temperature gas refrigerant from the compressor 1 is supplied to the outdoor heat exchanger 2, defrosting progresses, and after complete defrosting, the outdoor heat exchanger 2 2, the temperature rises due to the flow of high temperature gas refrigerant. Therefore, completion of defrosting is determined by determining in advance the high temperature state (for example, 8° C.) that will be obtained after the completion of defrosting and setting this as the return temperature Td2. On the other hand, the step S7 is a step for determining the end of the defrosting operation based on the defrosting operation continuation time td. The amount of frost is large and the above Te is
If defrosting operation is required for a long time to reach Td2, the room temperature will gradually drop during this time, causing great discomfort to the user. Therefore, the maximum allowable time for defrosting operation is the standard time (for example, 5
minutes), and when the defrosting operation time td reaches the above reference time, the defrosting operation is forcibly stopped even if there is unmelted frost attached to the outdoor heat exchanger 2. Heating operation has been restarted to ensure that indoor air conditioning comfort is not significantly compromised. Therefore, the above-mentioned step S7 is a step constituting the forced return means 73, and when the defrosting operation is terminated by this processing step S7,
This leaves some melted residue, and the defrosting operation measurement time td remains at 5 minutes. On the other hand, when the defrosting operation is completed in the processing step S6, the defrosting is completed and td is 5.
Holds measurements of less than a minute.

After the defrosting operation is completed as described above, at step S8, which constitutes the counting means 74, 1 is added to the counter bit n. At startup, -2 is initially set, so the above process makes n=-1. Then step S9
In this step, branch processing is performed depending on the content of n, and as described above, when the first defrosting operation after startup is completed, n=-1, so the process moves to step S10. Thereafter, n has a function of counting the number of defrosting operations, and in step S10 is newly set as n=1, that is, a content value that indicates that one defrosting operation has been completed. Next, in steps S11 and S12, as mentioned above, frost has already formed on the outdoor heat exchanger 2 at the start of the heating operation, and as a result, the subsequent heating operation performance may be kept low and sufficient recovery may not be possible. Determine the case. In other words, the first heating operation after the start of heating operation was performed for only 20 minutes (step S11), that is, Te had already fallen below Td within the heating priority period, and the defrosting operation was performed for 5 minutes. What happened (steps)
S12), that is, the process is forcibly returned with the remaining melt remaining, and in that case, the process moves from step S12 to step S13. At this time, if the answer is NO in either step S11 or S12, the process returns to step S2 and the heating operation is resumed in the same manner as described above.

In step S13, the heating operation is resumed in order to recover the room temperature that has dropped during the defrosting operation. The driving time is the first priority time (20 minutes).
The second priority time (for example, 10 minutes) is set shorter than that. The maximum allowable time for defrosting operation is set so that the room temperature that rises after at least 20 minutes of heating operation will decrease only slightly during the defrosting operation period, and therefore heating operation will be resumed. The subsequent recovery of room temperature can be accomplished in a shorter time.
Therefore, as mentioned above, the restarted heating operation time is shortened, and although this shortens the operation duration for maintaining the room temperature at the set temperature, the growth of frost on the outdoor heat exchanger 2 during this time is suppressed. Therefore, more complete defrosting can be performed in the next forced defrosting operation. When step S13 is completed, the process proceeds to step S5 via step S14, and a forced defrosting operation is performed. Step S14 above
is a processing step in which the count bit n is reset each time the forced defrosting operation is performed, and by setting a new value of -1 here, it is set to 0 in step S8 when the forced defrosting operation is completed. It will be fixed. When the forced defrosting operation starts in step S5, the step S5 is started as described above.
The operation is stopped according to the end determination condition in S6 or S7, and then from steps S8 and S9, the process moves to step S2 while maintaining the value n=0, and the heating operation is resumed.

Then, in steps S2 to S4, the first
After the heating operation continues during the priority time, the defrosting operation is switched to the defrosting operation based on the determination result of Te in the same manner as described above, and after the defrosting operation is performed in steps S5 to S7, the switching to n is performed in step S8. 1 is added. Next, the process returns from step S9 to S2, and the heating operation and defrosting operation are repeated in the same step process. And during this repetition, n is 5
, step S9 to step S12 is reached.
Then, it is determined whether or not there is any unmelted material remaining at the end of the previous defrosting operation based on whether the td=5 minutes or not. That is, the above steps S9 and S12 are processing steps constituting the forced signal generating means 75.
If S12 is YES, forced defrosting operation switching means 7
6, proceeding to steps S13 and S14,
After performing the heating operation for 10 minutes in the same manner as described above, proceed to step S5 to perform the forced defrosting operation, and reset n to 0 in steps S14 and S8.
Thereafter, the process returns to step S2 and the same process is continued again. If the determination condition for td = 5 minutes is NO in step S12, that is, if there is no unmelted material, the heating operation from step S2 is restarted, and every time the defrosting operation is performed thereafter, n is set to 5 or more. It will be added as the value of . and n
is 5 or more, the process moves from step S9 to S12 at the end of each defrosting operation, and the remaining melt is determined.
When the result is YES, the process moves to the above-mentioned forced defrosting operation, and n is reset to 0.

As explained above, in the above embodiment, when forced defrosting operation is performed after five defrosting operations have been performed after startup, or after performing the first defrosting operation after startup, , After this forced defrosting operation, after 5 defrosting operations, the presence or absence of melted residue is determined by td = 5.
Operation continues while making determinations in minutes. In other words, air-conditioning comfort inside the room is first ensured by the heating operation performed during the above-mentioned at least five defrosting operations, and then, if there is any remaining melt, the heating operation is performed during the second priority time, which is shorter than the first priority time. After performing heating operation,
A forced defrost operation is performed to restore the heating capacity of the device. After this forced defrosting operation,
After the defrosting operation is repeated five times, the operation is continued while similarly determining whether there is any remaining melt.
Therefore, even if unmelted material remains, operation can be continued while properly restoring the heating performance of the device without significantly impairing indoor air conditioning comfort, resulting in improved heating operation efficiency compared to conventional methods. Improvement is possible.

Note that the above embodiments do not limit this invention, and various changes can be made within the scope of this invention. For example, each numerical value such as the comparative discrimination value of the number of defrosting operations and the first priority time may be changed depending on the operating conditions. It is possible to change it as appropriate. Further, in the above embodiment, the frost amount detection means is the temperature detection sensor 40 of the outdoor heat exchanger 2.
However, other configurations using a magnetostrictive element or the like that can detect the frosting state based on the amount of elastic wave propagation loss are also possible. Furthermore, in the above embodiment, an air conditioner equipped with two indoor units A and B was described, but the same method can be applied to an air conditioner equipped with one or two or more indoor units. It is possible. Further, this invention can be similarly implemented in any type of compressor, regardless of whether the compressor 1 is an inverter type or a strain type compressor.

(Effects of the invention) As mentioned above, in the air conditioner of this invention, even if unmelted remains occur during defrosting operation within the predetermined allowable defrosting operation time, indoor air conditioning comfort will be significantly impaired. The heating capacity of the device is restored by removing the undissolved residue as appropriate.
Therefore, heating operation efficiency can be improved.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram of this invention, Fig. 2 is a refrigerant circuit diagram of an air conditioner in an embodiment of this invention, Fig. 3 is a control system block diagram of the above device, and Fig. 4 is a heating system in the above device. It is a flowchart of switching control between operation and defrosting operation. 1...Compressor, 2...Outdoor heat exchanger, 5, 6...
... Indoor heat exchanger, 40 ... External heat exchanger temperature detection sensor (frost formation amount detection means), 60 ... Operation mode selection section (operation control means), 71 ... Heating priority means, 72 ...
...Frost formation amount comparison means, 73...Forcible return means, 74
...Counting means, 75...Forced signal generation means,
76... Forced defrosting operation switching means.

Claims (1)

[Scope of utility model registration request] The air conditioner performs heating operation by circulating the gas refrigerant discharged from the compressor 1 from the indoor heat exchangers 5 and 6 to the outdoor heat exchanger 2, and the amount of frost formed on the outdoor heat exchanger 2 is controlled. A frost amount detection means 40 for detecting,
A frost amount comparison means 72 generates a defrost start signal when the detected frost amount exceeds a reference value, and a defrost end signal when the detected frost amount reaches a reset value, and a heating source when the defrost start signal is input. An operation control means 60 that switches from the operation to the defrosting operation, ends the defrosting operation and restarts the heating operation when a defrosting end signal is input, and when the duration of the defrosting operation reaches a reference time. A forced return means 73 issues a defrosting end signal to the operation control means 60, and an operation control means 60 receives a defrost start signal from the frost amount comparison means 72 until the first priority time elapses when restarting the heating operation. a heating priority means 71 that blocks input to the input, a counting means 74 that counts the number of defrosting operations, and a forced return means 73 that terminates the defrosting operation after the count value exceeds a predetermined value. A forced signal generating means 75 generates a forced defrosting signal when the forced defrosting signal is received from the defrosting end signal, and when the forced defrosting signal is generated, the restarted heating operation starts from the first priority time. An air conditioner comprising forced defrosting operation switching means 76 for issuing a defrosting start signal and resetting the count value of the counting means 74 after the short second priority time has been continued.