1

HVACR317 - Refrigeration

Commercial Refrigeration Diagrams

2

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

DIAGRAM “A”

1

COMPRESSOR

3

• 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.

H.O. SLIDE 1

4

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

POWER SWITCH CLOSED

2

5

• Like any system, fan, fan, and compressor will sequence in parallel.

• The start cap will provide the required torque to the start winding.

H.O. SLIDE 2

6

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

NORMAL RUNNING CYCLE

3

7

• 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.

H.O. SLIDE 3

8

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

BOX REACHES 0 – 10 º F

4

9

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

H.O. SLIDE 4

10

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

BOX TEMP GOES UP…TSTAT CLOSES

11

TIMER MOTOR

2

NO

HGSNC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

DEFROST CYCLE

5

12

• When the timer switches to defrost, compressor stays on, and HGS energizes.

• The EFM is de-energized in defrost.

H.O. SLIDE 5

13

HOT GAS DEFROST (PIPING) REMINDER….NORMAL OPERATION…..

C

MD

CONDENSER

EVAPORATOR

OFF

14

HOT GAS DEFROST (PIPING) REMINDER….DEFROST CYCLE…..

C

MD

CONDENSER

EVAPORATOR

EFM SHUTS

OFF

ON

15

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

DIAGRAM “B”

6

COMPRESSOR

N

3

4

X DTT

LIMIT

16

• 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

H.O. SLIDE 6

17

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

POWER ON

7

COMPRESSOR

N

3

4

X DTT

LIMIT

18

• 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).

H.O. SLIDE 7

19

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

DEFROST CYCLE

8

COMPRESSOR

N

3

4

X DTT

LIMIT

20

• 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.”

H.O. SLIDE 8

21

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

9

COMPRESSOR

N

3

4

X DTT

LIMIT

DEFROST TERMINATION

22

• 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).

H.O. SLIDE 9

23

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

10

COMPRESSOR

N

3

4

X DTT

LIMIT

DEFROST IS TERMINATED..BUT NO EFM

24

• 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.

H.O. SLIDE 10

25

HOT PULL DOWN EXAMPLE: PRESENTLY THE SYSTEM IS RUNNING NORMAL (R134a). THE SYSTEM PRESSURES WILL

GENERALLY RUN 5 TO 20 PSIG………

C

MD

CONDENSER

EVAPORATOR

5 150

26

WHEN THE SYSTEM GOES INTO DEFROST THE EVAP COIL HEATS UP AND THE PRESSURES ARE

BASICALLY EQUALIZED

OFF

MD

CONDENSER

EVAPORATOR

100100

HEATERS ON

27

WHEN DEFROST IS TERMINATED, THE EXTREME HEAT LOAD ON THE COIL COULD CAUSE AN OVERLOAD ON THE

ELECTRICAL CIRCUIT AND TRIP A BREAKER….

C

MD

CONDENSER

EVAPORATOR

50 170

…DELAYING THE EFM IS ONE WAY TO KEEP THE PRESSURES DOWN AT INITIAL START

UP

TOO HIGH

28

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

EVAP GETS COLD…EFM GOES ON

11

COMPRESSOR

N

3

4

X DTT

LIMIT

29

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

DTT SWITCHED “DOWN”

11

COMPRESSOR

N

3

4

X DTT

LIMIT

30

• 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.

H.O. SLIDE 11

31

TIMER MOTOR

2

NO

DH

NC

EFM

TS

LPS

HPS

LAC CFM

R C

S

1 2 5

SC

12

COMPRESSOR

N

3

4

X DTT

LIMIT

PURPOSE OF THE “LIMIT”

32

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

H.O. SLIDE 12

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

C

MD

CONDENSER

EVAPORATOR

34

LPS

CFM

R C

S

1 2 5

SC

DIAGRAM “C”

13

COMPRESSOR

EFM

TM X

4

N

35

• 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).

H.O. SLIDE 13

36

LPS

LAC CFM

R C

S

1 2 5

SC

DIAGRAM “C”

14

COMPRESSOR

EFM

TM X

4

N

37

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.

H.O. SLIDE 14

38

LPS

CFM

R C

S

1 2 5

SC

DIAGRAM “D”

15

COMPRESSOR

EFM

R134A: 30 # DIFF.

CI:50 psig CO: 20 psig

39

• 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.

H.O. SLIDE 15