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HVACR317 – Core for Refrigeration

HVACR317 – Core for Refrigeration. Operating Controls 2 Pressure Switches Oil Pressure Safety. Pressure Switches. Pressure switches are used to start and stop electrical loads such as motors or coils.

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HVACR317 – Core for Refrigeration

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  1. HVACR317 – Core for Refrigeration Operating Controls 2 Pressure Switches Oil Pressure Safety

  2. Pressure Switches • Pressure switches are used to start and stop electrical loads such as motors or coils. • Pressure controls contain a bellows, a diaphragm, or a Bourdon tube to create movement when the pressure is changed.

  3. Pressure Switches • When used as a switch the bellows or tube is connected to linkage that operates the electrical contacts. • When used as a valve they operate the valve directly. • The electrical contacts are the components that actually open and close the circuit.

  4. Pressure Switch • The electrical contacts either open or close with a snap action on a rise in pressure. • The pressure switch can also sense a pressure differential and be designed to open or close a set of electrical contacts based on this differential.

  5. Pressure Switch • The pressure control can either be an operating type control or a safety type control. • It can operate either at low or high pressures depending on the type of design.

  6. Pressure Switch • Pressure controls can sometimes be recognized by the small line running to them for measuring fluid pressures. • Pressure switches are manufactured to handle control voltages or line currents to start a compressor up to 3 hp maximum.

  7. Pressure Switch • The high pressure and low pressure controls in the refrigeration and air conditioning industry are the most two widely used pressure controls in the industry.

  8. Pressure Switch • Some pressure switches are adjustable and some are not. • Some controls are automatic reset and some are manual reset. • In some pressure controls the high-pressure and low-pressure controls are built into one housing.

  9. Pressure Switch • The point or pressure setting at which the control interrupts the electrical circuit is known as the cut-out. • The point or pressure setting at which the electrical circuit is made is known as the cut-in. • The difference in the two settings is known as the differential.

  10. Pressure Switch Differential Controls pressure

  11. Pressure Switch Differential Controls temperature through pressure.

  12. Pressure Switch

  13. Pressure Switch

  14. Pressure Switch

  15. Pressure Controls - High • High Pressure controls open on a rise in pressure. • If you hold a high pressure control in your hand at room pressure it is closed. • Primarily used as a safety device to shut off compressor if pressure rise to high.

  16. Pressure Controls - High • Most high pressure controls have a manual reset. • This is to prevent cycling in an unsafe condition.

  17. Pressure Switch - High Type

  18. Pressure Controls - High

  19. Pressure Switch - Ranco

  20. Pressure Switch

  21. Pressure Switch - Low • Low pressure switches are used to sense a drop in pressure. • Most often the low switch is used to sense a loss of charge or refrigerant. • The low pressure switch is also used to control the compressor in a pump-down system.

  22. Pressure Switch - Low • It is not desirable to run a system with a low charge because: • The compressor motors use refrigerant to cool the windings. • If the system goes into a vacuum because of a leak it may pull air and noncondensable gases into the system and cause more damage.

  23. Pressure Switch - Low

  24. Pressure Switch - Combo

  25. Oil Pressure Safety • The oil pressure safety switch is a low and high pressure switch that is a pressure differential control. • The differential control takes the high and low pressure and compares the two numbers coming up with a net pressure.

  26. Oil Pressure Safety • The net oil pressure is the higher number minus the lower number. • The net oil pressure is the useable oil pressure.

  27. Oil Pressure Safety

  28. Oil Pressure Safety • The oil pressure is caused by a pump attached to the crankshaft of the compressor. • When the compressor is not running there is no oil pressure. • Because of this the oil pressure safety contains a timer that delays the action of the switch for roughly 90 seconds.

  29. Oil Pressure Safety

  30. Oil Pressure Safety • The oil pressure is measured between the suction side (compressor crankcase) and the oil pump outlet. • Most compressors must have a minimum of 30psi of oil pressure. • Always follow manufactures directions. • Oil pressure safety controls have a manual reset.

  31. Oil Pressure Safety

  32. Pressure Switch Symbols

  33. PRESSURE STATE with CUT-IN/OUT ADJUSTMENTS

  34. VARIOUS PRESSURE STATS (2-Position | ON/OFF)

  35. LOW PRESSURE HIGH PRESSURE SWITCHES

  36. DEFROST TIMER SWITCH

  37. TIMING MOTOR TIMED CONTACTS DEFROST TIMER SWITCH

  38. COMPRESSOR ANTI-SHORT CYCLE SWITCH

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