Refrigerant charge level detection

1. A refrigerant charge monitoring system comprising:

a first sensor operable to provide an output indicative of a sensed refrigerant liquid temperature of a liquid refrigerant line that is within or extending from an outlet of a condenser coil of an air conditioner or heat pump unit;

a second sensor operable to provide an output indicative of a sensed refrigerant liquid pressure of the liquid refrigerant line; and

a controller configured to determine at least one target pressure value from the output indicative of the sensed refrigerant liquid temperature, the controller being configured to determine if the level of refrigerant charge is at, above, or below an acceptable level based on a comparison of the output indicative of sensed refrigerant liquid pressure to the at least one target pressure value;

wherein the controller is a processor of a thermostat that is configured to wirelessly receive the output indicative of sensed pressure and the output indicative of a sensed temperature of a liquid refrigerant line.

2. The system of claim 1 , wherein:

the first sensor is operable to sense the temperature of the liquid refrigerant line at the outlet of the condenser coil; and

the second sensor is operable to sense the pressure of the liquid refrigerant line at the outlet of the condenser coil.

3. The system of claim 1 , further comprising a display that displays an indication of whether the level of refrigerant charge is at, above, or below an acceptable level.

4. The system of claim 1 , wherein the controller is configured to determine at least one target pressure value by converting at least the sensed refrigerant liquid temperature of the liquid refrigerant line into a corresponding pressure value based on a temperature-pressure relationship for the refrigerant.

5. The system of claim 1 , wherein the controller is configured to compare the output indicative of sensed refrigerant liquid pressure to at least one target pressure value to determine if the sensed refrigerant liquid pressure is below a minimum threshold indicative of a low refrigerant charge level.

6. The system of claim 1 , wherein the controller is configured to compare the output indicative of sensed refrigerant liquid pressure to at least one target pressure value to determine if the sensed refrigerant liquid pressure exceeds a threshold indicative of a high refrigerant charge level.

7. The system of claim 1 , wherein the controller is configured to determine a difference between the output indicative of sensed refrigerant liquid pressure and at least one target pressure value, and to display on a display device an indication of a low refrigerant charge level where the difference exceeds a threshold indicative of a low refrigerant charge level.

8. The system of claim 1 , wherein the controller is a processor of a control for activating at least a compressor of an air conditioner or heat pump.

9. The system of claim 1 , wherein the controller is a communication device for communicating information indicating that the refrigerant charge is at, above, or below an acceptable level based on a comparison of the output indicative of sensed pressure to the at least one target pressure value.

10. The system of claim 1 , further comprising a display of the thermostat configured to display an indication of whether the level of refrigerant charge is at, above, or below an acceptable level.

11. A refrigerant charge monitoring system comprising:

a first sensor operable to provide an output indicative of a sensed refrigerant liquid temperature of a liquid refrigerant line that is within or extending from an outlet of a condenser coil of an air conditioner or heat pump unit;

a second sensor operable to provide an output indicative of a sensed refrigerant liquid pressure of the liquid refrigerant line; and

a controller configured to determine at least one target pressure value from the output indicative of the sensed refrigerant liquid temperature, the controller being configured to determine if the level of refrigerant charge is at, above, or below an acceptable level based on a comparison of the output indicative of sensed refrigerant liquid pressure to the at least one target pressure value;

wherein the controller is configured to determine if the sensed refrigerant liquid pressure is within a range defined by at least two target pressure values representative of a sensed refrigerant level that is above, below, or within an acceptable range.

12. The system of claim 11 , further comprising a display configured to display at least one of one or more indicators for indicating that the sensed refrigerant level is above, below, or within the acceptable range, and wherein the display displays one or more indicators representing a relative scale for indicating whether the sensed refrigeration level is above, below or within the acceptable range.

13. The system of claim 11 , wherein the controller is a processor of a thermostat that is configured to wirelessly receive the output indicative of sensed pressure and the output indicative of a sensed temperature of a liquid refrigerant line.

14. A refrigerant charge monitoring system comprising:

a first sensor operable to provide an output indicative of a sensed refrigerant liquid temperature of a liquid refrigerant line that is within or extending from an outlet of a condenser coil of an air conditioner or heat pump unit;

a second sensor operable to provide an output indicative of a sensed refrigerant liquid pressure of the liquid refrigerant line; and

a controller configured to determine at least one target pressure value from the output indicative of the sensed refrigerant liquid temperature, the controller being configured to determine if the level of refrigerant charge is at, above, or below an acceptable level based on a comparison of the output indicative of sensed refrigerant liquid pressure to the at least one target pressure value;

wherein the controller is configured to determine at least two target pressure values and to compare the output indicative of sensed refrigerant liquid pressure to the plurality of target pressure values to determine if the sensed refrigerant liquid pressure is between at least two target pressure values that are indicative of an acceptable range for a sensed refrigerant charge level.

15. A method for monitoring refrigerant charge, the method comprising:

sensing and providing a first output indicative of a sensed refrigerant liquid temperature of a liquid refrigerant line that is within or extending from an outlet of a condenser coil of an air conditioner or heat pump unit;

sensing and providing a second output indicative of a sensed refrigerant liquid pressure of the liquid refrigerant line;

determining at least one target pressure value from the output indicative of the sensed refrigerant liquid temperature of the liquid refrigerant line; and

determining if the level of refrigerant charge is at, above, or below an acceptable level based on a comparison of the output indicative of sensed refrigerant liquid pressure to the at least one target pressure value;

wherein:

determining if the level of refrigerant charge is at, above, or below an acceptable level comprises determining if the sensed refrigerant liquid pressure is within an acceptable range defined by at least two target pressure values; and

the method further comprises displaying at least one of one or more indicators for indicating whether the level of refrigerant charge is above, below, or within the acceptable range.

16. The method of claim 15 , wherein:

sensing and providing a first output indicative of a sensed refrigerant liquid temperature of a liquid refrigerant line comprises sensing the temperature of the liquid refrigerant line at the outlet of the condenser coil; and

sensing and providing a second output indicative of a sensed refrigerant liquid pressure of the liquid refrigerant line comprises sensing the pressure of the liquid refrigerant line at the outlet of the condenser coil.

17. The method of claim 15 , wherein determining at least one target pressure value comprises converting at least the sensed refrigerant liquid temperature of the liquid refrigerant line into a corresponding pressure value based on a temperature-pressure relationship for the refrigerant.

18. The method of claim 15 , wherein:

determining if the level of refrigerant charge is at, above, or below an acceptable level comprises comparing the output indicative of sensed refrigerant liquid pressure to at least one target pressure value to determine if the sensed refrigerant liquid pressure is below a minimum threshold indicative of a low refrigerant charge level; and

the method further includes displaying an indication of a low refrigerant charge level.

19. The method of claim 15 , wherein:

determining if the level of refrigerant charge is at, above, or below an acceptable level comprises comparing the output indicative of sensed refrigerant liquid pressure to at least one target pressure value to determine if the sensed refrigerant liquid pressure exceeds a threshold indicative of a high refrigerant charge level; and

the method further includes displaying an indication of a high refrigerant charge level.