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HVACR317 - Refrigeration

HVACR317 - Refrigeration. Commercial Refrigeration Diagrams. DIAGRAM “A”. TIMER MOTOR. 2. NO. HGS. NC. EFM. LAC. CFM. TS. R. C. LPS. COMPRESSOR. S. HPS. SC. 1. 1 2 5. H.O. SLIDE 1.

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HVACR317 - Refrigeration

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  1. HVACR317 - Refrigeration Commercial Refrigeration Diagrams

  2. DIAGRAM “A” TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 1 1 2 5

  3. H.O. SLIDE 1 • The first diagram represents a typical self-contained reach-in box. • It is a low temp system using hot gas defrost. • The compressor is CSIR. • The LAC (Low Ambient Control) would be used if the condensing unit is installed outdoors. • The Run cap is optional.

  4. POWER SWITCH CLOSED TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS S HPS SC 2 1 2 5

  5. H.O. SLIDE 2 • Like any system, fan, fan, and compressor will sequence in parallel. • The start cap will provide the required torque to the start winding.

  6. NORMAL RUNNING CYCLE TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS S HPS SC 3 1 2 5

  7. H.O. SLIDE 3 • The BEMF energizes the relay and drops out the start cap. • The system will cycle normally on the (Honeywell/White Rogers/Johnson Controls) remote bulb thermostat.

  8. BOX REACHES 0 – 10 º F TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS S HPS SC 4 1 2 5

  9. H.O. SLIDE 4 • When the box temperature reaches 0 – 10° F (typical setting), the thermostat opens. EFM and TM continue to run.

  10. BOX TEMP GOES UP…TSTAT CLOSES TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS S HPS SC 1 2 5

  11. DEFROST CYCLE TIMER MOTOR 2 NO HGS NC EFM LAC CFM TS R C LPS S HPS SC 5 1 2 5

  12. H.O. SLIDE 5 • When the timer switches to defrost, compressor stays on, and HGS energizes. • The EFM is de-energized in defrost.

  13. HOT GAS DEFROST (PIPING) REMINDER….NORMAL OPERATION….. EVAPORATOR C CONDENSER OFF MD

  14. HOT GAS DEFROST (PIPING) REMINDER….DEFROST CYCLE….. EVAPORATOR C ON CONDENSER EFM SHUTS OFF MD

  15. DIAGRAM “B” TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 6 1 2 5

  16. H.O. SLIDE 6 • This system is also low temp, but using electric defrost. • This type of system has an evap fan “delay” sequence. • It uses two “DTT” type controls. • It also has the ability to disengage the timer out of defrost. • STEP BY STEP SEQUENCE IS COMING UP

  17. POWER ON TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 7 1 2 5

  18. H.O. SLIDE 7 • Just like the last system, fan, fan, compressor are running. • The DTC timer is line-to-line, like the last system. • A different type (or model) DTC is used. Notice the extra terminals on the timer. • The device between “3” and “X” is a solenoid (more on that later).

  19. DEFROST CYCLE TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 8 1 2 5

  20. H.O. SLIDE 8 • The only path is through the heater and “limit.” All else is Off. • The limit “acts as” a DTT (like the domestic units), but it has a higher temp (cut-out) rating than the domestic types. It is basically a high-temp safety. • The “actual” DTT is the SPDT one just below the “limit.”

  21. DEFROST TERMINATION TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 9 1 2 5

  22. H.O. SLIDE 9 • When the SPDT DTT senses that the evap coil is warm enough, it will switch up to the top circuit, completing a path to the “clutch solenoid” on the DTC. • The solenoid will swap the contacts back into refrigeration mode (no waiting).

  23. DEFROST IS TERMINATED..BUT NO EFM TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 10 1 2 5

  24. H.O. SLIDE 10 • The evap fan has not come on yet due to the warm evap coil. • When the DTT cools back down, the switch will drop back in, and the evap fan will restart. • The purpose of this control (and sequence) is to prevent a ‘hot pull-down’ situation after each defrost cycle.

  25. HOT PULL DOWN EXAMPLE: PRESENTLY THE SYSTEM IS RUNNING NORMAL (R134a). THE SYSTEM PRESSURES WILL GENERALLY RUN 5 TO 20 PSIG……… EVAPORATOR C CONDENSER 5 150 MD

  26. WHEN THE SYSTEM GOES INTO DEFROST THE EVAP COIL HEATS UP AND THE PRESSURES ARE BASICALLY EQUALIZED EVAPORATOR OFF CONDENSER 100 100 HEATERS ON MD

  27. WHEN DEFROST IS TERMINATED, THE EXTREME HEAT LOAD ON THE COIL COULD CAUSE AN OVERLOAD ON THE ELECTRICAL CIRCUIT AND TRIP A BREAKER…. EVAPORATOR C CONDENSER 50 170 TOO HIGH MD …DELAYING THE EFM IS ONE WAY TO KEEP THE PRESSURES DOWN AT INITIAL START UP

  28. EVAP GETS COLD…EFM GOES ON TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 11 1 2 5

  29. DTT SWITCHED “DOWN” TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 11 1 2 5

  30. H.O. SLIDE 11 • Like all (domestic or commercial) automatic defrost system,s this defrost circuit can be terminated by time and / or temperature. • The main advantage of using this type of timer is that the refrigeration mode can be brought back instantly if the DTT duration exceeded a few minutes.

  31. PURPOSE OF THE “LIMIT” TIMER MOTOR N 2 3 LIMIT DH NO X DTT NC 4 EFM LAC CFM TS R C LPS COMPRESSOR S HPS SC 12 1 2 5

  32. H.O. SLIDE 12 • If the SPDT DTT should fail, the limit will provide a lockout condition if an overheating situation should occur.

  33. ELECTRIC DEFROST REMINDERS…THE ELEMENT IS EITHER ON OR BELOW THE EVAP COIL…DTT AND LIMIT ARE BOTH LOCATED ON EVAP COIL EVAPORATOR C CONDENSER MD

  34. DIAGRAM “C” EFM N TM X 4 CFM R C LPS COMPRESSOR S SC 13 1 2 5

  35. H.O. SLIDE 13 • This system is a medium temp application (EFM is line-to-line). • The defrost cycle simply shuts down the compressor circuit (sometimes done in the late evening hours). A simple timer is used. • The LP switch is used as a temperature control (not the best way to go, but it is common).

  36. DIAGRAM “C” EFM N TM X 4 LAC CFM R C LPS COMPRESSOR S SC 14 1 2 5

  37. H.O. SLIDE 14 Using an LP switch as a thermostat: • Set the LP switch to its recommended settings (C.I. & C.O.). Attach gauges. • Place a thermometer in the box and close the door. • When the box reaches the desired temp (e.g., 35° F), set the C.O. of the LP switch to the low side pressure shown on the gauge.

  38. DIAGRAM “D” EFM R134A: 30 # DIFF. CI:50 psig CO: 20 psig LPS CFM R C COMPRESSOR S SC 15 1 2 5

  39. H.O. SLIDE 15 • High or medium temp system: • Uses Off Cycle Defrost • Off cycle defrost can be set up by adjusting the LP switch differential higher than normal. • The 30 psig differential allows sufficient time for defrost.

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