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HVACR318 - Refrigeration

HVACR318 - Refrigeration. Pump Down Systems Pressure Switches Solenoid Valves. Solenoid Valves. Solenoid Valves are a mechanical/electrical valve. The mechanical part is in the refrigeration or water line. The electrical portion is a coil that is attached to the top of the valve.

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HVACR318 - Refrigeration

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  1. HVACR318 - Refrigeration Pump Down Systems Pressure Switches Solenoid Valves

  2. Solenoid Valves • Solenoid Valves are a mechanical/electrical valve. • The mechanical part is in the refrigeration or water line. • The electrical portion is a coil that is attached to the top of the valve.

  3. Solenoid Valves

  4. Solenoid Valve • The valve in the closed position is not powered and the flow of liquid is being blocked by the plunger in the DOWN position. • In the closed position the coil does not produce any magnetic field as it is not powered.

  5. Solenoid Valve - Closed Valve is blocking flow of liquid.

  6. Solenoid Valve - Open • The valve opens when the coil is powered. • The coil generates a magnetic field and pulls the plunger into the up position. • This allows fluid flow through the central passage of the valve.

  7. Solenoid Valve - Opening

  8. Solenoid Valve - Open

  9. Solenoid Valves • In refrigeration solenoid valves mainly have two uses • Hot Gas By-Pass Defrost • Pump Down Systems

  10. Pump Down System • The solenoid in the pump down system is used in the liquid line prior to the metering device and after the receiver. • The solenoid is in the normally closed position. • When the thermostat calls for cooling the solenoid opens.

  11. Pump Down System • This releases refrigerant into the liquid line and raises the pressure of the system. • A pressure switch senses this pressure increase and turns on the compressor. • When the call for cooling is complete the thermostat de-energizes the solenoid

  12. Pump Down System • The solenoid closes and blocks the flow of refrigerant into the liquid line. • The refrigerant gets pumped into the receiver which is mounted after the condenser coil. • Once the refrigerant is pumped down into the receiver the pressure on the system drops.

  13. Pump Down System • Once the pressure has dropped to a pre-determined point the pressure switch opens and shuts off the compressor.

  14. Pump down system • The thermostat controls the solenoid - not the compressor. • The pressure switch controls the compressor. • The purpose of a pump down system is to prevent liquid refrigerant from migrating to the evaporator on off cycles.

  15. Pump down system • If liquid refrigerant is in the evaporator it will be sucked as a liquid into the compressor on start up. • Liquid refrigerant in the compressor can break valves, crank shafts and cause premature compressor failure.

  16. Pump Down Systems • Commercial freezers are low temperature and commercial refrigerators are medium temperature. • Both common to have pump down systems for commercial applications. • Low temp systems • Medium temp systems

  17. Pump Down OFF Cycle EVAPORATOR C 20 CONDENSER 100 OFF MD OFF `

  18. Pump Down Starting Cycle EVAPORATOR C 35 CONDENSER 100 OFF ON MD

  19. Pump Down On Cycle EVAPORATOR C 40 CONDENSER 150 ON ON MD

  20. Pump Down Satisfied Cycle EVAPORATOR C 30 CONDENSER 150 ON OFF MD

  21. Pump Down OFF Cycle EVAPORATOR C 20 CONDENSER 100 OFF MD OFF `

  22. Pump Down Schematic L1 SS N R C S C1 Setpoint: 35 degrees F. Temp is 55 Degree F.

  23. 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.

  24. 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.

  25. 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.

  26. 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.

  27. 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.

  28. 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.

  29. 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.

  30. 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.

  31. Pressure Switch Differential Controls pressure

  32. Pressure Switch Differential Controls temperature through pressure.

  33. Pressure Switch

  34. Pressure Switch

  35. Pressure Switch

  36. 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.

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

  38. Pressure Switch - High Type

  39. Pressure Controls - High

  40. Pressure Switch - Ranco

  41. Pressure Switch

  42. 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.

  43. 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.

  44. Pressure Switch - Low

  45. Pressure Switch - Combo

  46. 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.

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

  48. Oil Pressure Safety

  49. 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.

  50. Oil Pressure Safety

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