The rotating blade rotary compressor has its roller centered on a shaft that is eccentric to the center of the cylinder. Two spring-loaded roller blades are mounted 180° apart. They sweep the sides of the cylinder. The roller is mounted so that it touches the cylinder at a point between the intake and the discharge ports. The roller rotates. In rotating, it pulls
the vapor into the cylinder through the intake port. Here, the vapor is trapped in the space between the cylinder wall, the blade, and the point of contact between the roller and the cylinder. As the next blade passes the contact point, the vapor is compressed. The space or the vapor becomes smaller and smaller as the blade rotates.
Once the vapor has reached the pressure determined by the compressor manufacturer, it exits through the discharge port to the condenser.
On this type of rotating blade rotary compressor the seals on the blades present a particular problem. There also are lubrication problems. However, a number of rotary compressors are still in operation in home refrigerators.
Some manufacturers make rotary blade compressors for commercial applications. They are used primarily with ammonia. Thus, there is no copper or copper alloy tubing or parts. Most of the ammonia tubing and working metal is stainless steel.
The only moving parts in a stationary blade rotary compressor are a steel ring, an eccentric or cam, and a sliding barrier (see Fig. 9-71). Figure 9-72 shows how the rotation of the off-center cam compresses the gas refrigerant in the cylinder of the rotary compressor. The cam is rotated by an electric motor. As the cam spins it carries the ring with it. The ring rolls on its outer rim around the wall of the cylinder.
To be brought into the chamber, the gas must have a pathway. Note that in Fig. 9-73 the vapor comes in from the freezer and goes out to the condenser through holes that have been drilled in the compressor frame. Note that an offset rotating ring compresses the gas. Figure 9-74 shows how the refrigerant vapor in the compressor is brought from the freezer. Then, the exit port is opening. When the compressor starts to draw in the vapor from the freezer the barrier is held against the ring by a spring.
This barrier separates the intake and exhaust ports. As the ring rolls around the cylinder it compresses the gas and passes it on to the condenser (see Fig. 9-75). The finish of the compression portion of the stroke or operation is shown in Fig. 9-76. The ring rotates around the cylinder wall. The spring tension of the barrier’s spring and the pressure of the
cam being driven by the electric motor hold it in place. This type of compressor is not used as much as the reciprocating hermetic type of compressor.
Process tubes are installed in compressor housings at the factory as an aid in factory dehydration and charging. These can be used in place of the suction tube if they are of the same diameter and wall thickness as the suction tube.
Standard discharge tubing arrangements for Tecumseh hermetic compressors are shown in Fig. 9-67. Discharge tubes are generally in the same position within any model family. Suction and process tube positions may vary.
Tecumseh, like other compressor manufacturers, made compressors for many manufacturers of refrigerators, air-conditioning systems, and coolers. Because of this, the same compressor model may be found in the field in many suction and discharge variations. Each variation depends upon the specific application for which the compressor was designed.
Suction connections can usually be identified as the stub tube with the largest diameter in the housing. If two stubs have the same outside diameter, then the one with the heavier wall will be the suction connection. If both of the largest stub tubes have the same outside diameter and wall thickness, then either can be used as the suction connection. However, the one farthest from the terminals is preferred.
The stub tube not chosen for the suction connection may be used for processing the system. Compressor connections can usually be easily identified. However, occasionally some question arises concerning oil cooler tubes and process tubes.
Oil cooler tubes are found only in low-temperature refrigeration models. These tubes connect to a coil or hairpin bend within the compressor oil sump (see Fig. 9-66). This coil or hairpin bend is not open inside the compressor. Its only function is to cool the compressor sump oil. The oil cooler tubes are generally connected to an individually separated tubing circuit in the air-cooled condenser.
There are four general types of single-phase motors. Each has distinctly different characteristics. Compressor motors are designed for specific requirements regarding starting torque and running efficiency. These are two of the reasons why different types of motors are required to meet various demands.
The resistance-start induction-run (RSIR) motor is used on many small hermetic compressors through 1/3 hp. The motor has low starting torque. It must be applied to completely self-equalizing capillary tube systems such as household refrigerators, freezers, small water coolers, and dehumidifiers.
This motor has a high-resistance-start winding that is not designed to remain in the circuit after the motor has come up to speed. A current relay is necessary to disconnect the start winding as the motor comes up to design speed (see Fig. 9-36).
The capacitor-start induction-run (CSIR) motor is similar to the RSIR. However, a start capacitor is included in series with the start winding to produce a higher starting torque. This motor is commonly used on commercial refrigeration systems with a rating through 3/4 hp (see Fig. 9-37).
Capacitor-start and -run
The capacitor-start and -run (CSR) motor arrangement uses a start capacitor and a run capacitor in parallel with each other and in series with the motor start winding. This motor has high starting torque and runs efficiently. It is used on many refrigeration and air-conditioning applications through 5 hp. A potential relay removes the start capacitor from the circuit after the motor is up to speed. Potential relays must be accurately matched to the compressor (see Fig. 9-38). Efficient operation depends on this.
Permanent split capacitor
The permanent split capacitor (PSC) has a run capacitor in series with the start winding. Both run capacitor and start winding remain in the circuit during start and after the motor is up to speed. Motor torque is sufficient for capillary and other self-equalizing systems. No start capacitor or relay is necessary. The PSC motor is basically an air-conditioning compressor motor. It is very common through 3 hp. It is also available in 4 and 5 hp sizes (see Fig. 9-39).
The CL compressor series is designed for residential and commercial air-conditioning and heat pumps. These compressors are made in 2-1/2, 3, 3-1/2, 4, and 5 hp sizes. They can be operated on three-phase or singlephase power (see Fig. 9-31). Since this is one of the larger compressors, it has two cylinders and pistons. It needs a good protection system for the motor. This one has an internal thermostat to interrupt the control circuit to the motor contactor. The contactor then disconnects the compressor from the power source. Figure 9-32 shows the location of the internal thermostat.
There is a supplementary overload in the compressor terminal box so it can be reached for service (see Fig. 9-33). Alocked rotor or another condition producing excessive current draw causes the bimetal disk to flex upward. This opens the pilot circuit to the motor contactor.
The contactor then disconnects the compressor from the power source. Single-phase power requires one supplementary overload (see Fig. 9-34). Three-phase power requires two supplementary overloads (see Fig. 9-35). This CL line of compressors uses R-22 and R-12 (R-134a) or its suitable substitute refrigerants. They also use an oil charge of either 45 or 55 oz. In some cases, when the units are interconnected, they use 65 oz.
The AJ series of air-conditioning compressors ranges in size from 1100 to 19,500 Btu (see Fig. 9-23). An oil charge of 26 or 30 oz is standard, depending upon the model. They are mounted on three or four points (see Fig. 9-24). A snap-on terminal cover allows quick access to the connections under the cover (see Fig. 9-25). This particular model has an antislug feature that is standard on all AJM 12 and larger models (see Fig. 9-26). (An anti-slug feature keeps the liquid refrigerant moving.)
This type of compressor relies upon the permanent split-capacitor motor. In this instance, the need for both start and run capacitor is not presented. The start relay and the start capacitor are eliminated in this arrangement (see Fig. 9-27). With the PSC motor, the run capacitor acts as both a start and run capacitor. It is never disconnected. Both motor windings are always engaged while the compressor is starting and running.
PSC motors provide good running performance and adequate starting torque for low line voltage conditions. They reduce potential motor trouble since the electrical circuit is simplified (see Fig. 9-28).
The figure shows a run capacitor designed for continuous duty. It increases the motor efficiency while improving power and reducing current drain from the line. Do not operate the compressor without the designated run capacitor. Otherwise, an overload results in the loss of start and run performance. Adequate motor overload protection is not available either. Arun capacitor in the circuit causes the motor to have some rather unique characteristics. Such motors have better pullout characteristics when a sudden load is applied.
Figure 9-29 shows how this particular series of compressors is wired for using the capacitor in the run and start circuit. Note the overload is an external line breaker. This motor overload device is firmly attached to the compressor housing. It quickly senses any unusual temperature rise or excess current draw. The bimetal disk reacts to either excess temperature or excess current draw. It flexes downward, thereby disconnecting the compressor from the power source (see Fig. 9-30).
The B and model compressors are available in 1/3, 1/2, 3/4, 1, 1-1/2, 1-3/4, and 2 hp units. All of them use a 45-oz charge of oil. They have a wide variety of temperature and air-conditioning applications. These models may have a B or a C preceding the model serial number. This is to indicate the series of compressors.
The AH compressors are designed for residential and commercial airconditioning and heat pump applications (see Fig. 9-17). They can be obtained with either three- or four-point mountings (see Fig. 9-18). The internal line-break motor protector is used. It is located precisely in the center of the heat sink position of the motor windings. Thus, it detects excessive motor winding temperature and safely protects the compressor from excessive heat and/or current flow (see Fig. 9-19).
The snap on terminal cover assembly is shown in Fig. 9-20. It is designed for assembly without tools. The molded fiberglass terminalcover may be secured or held in place by a bale strap.
This AH compressor series has a run capacitor in the circuit, as shown in Fig. 9-21. This compressor is designed for single-phase operation. Figure 9-22 shows the terminal box with the position of the terminals and the ways in which they are connected for run, start, and common.
The AH compressors are rated in Btu per hour. They range from 3500 to 40,000 Btu/h. These models use 45 oz of oil for the charge. They are used as air-conditioning units and for almost any other temperature range applications. They use R-134a or suitable substitute or R-22 for refrigerant.
The ISM (internal spring mount) series of compressors ranges in size from 1/8 to 1 hp. Their temperature range is from ?30 to 10°F (?34 to ?12°C) and from 20 to 55°F (?6 to 13°C). The oil charge is either 40 or 45 oz, depending upon the particular model.