1 hvacr317 - refrigeration commercial refrigeration diagrams
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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
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