Symbols

21 HVAC Industry Standards

In order to read and understand an electrical diagram you need to know how different controls and loads are drawn.

22 SYMBOLS

SINGLE POLE SINGLE THROW SPST

23 SYMBOLS

SINGLE POLE SINGLE THROW NORMALLY OPEN SPST - NO

24 SYMBOLS

SINGLE POLE SINGLE THROW NORMALLY CLOSED SPST - NC

25 SYMBOLS

DOUBLE POLE SINGLE THROW DPST – 2 NO

26 SYMBOLS

SINGLE POLE DOUBLE THROW SPDT

27 SYMBOLS

DOUBLE POLE DOUBLE THROW DPDT 28 Relays or Contactors R

Normally Closed Contact R

Normally Open Contact

Relay Coil Relays

C

Contactors

Contactor Coil C 29 Relays

L2

120v M

24v

c

30 Relays

L2

Large Current

120v M

24v Small Current

c

31 Relays or Contactors THE CONTACTS OF A RELAY OR CONTACTOR ARE DRAWN IN A DE-ENERGIZED CONDITION

32 Pressure Switches

High- Pressure Switch SPST Opens on Rise (Safety Control)

Low-Pressure SPST Opens on Drop Switch (Safety Control)

33 Pressure Switches

Air Pressure SPST Closes on Drop (Operating Control) Switch

SPST Closes on Rise Fan Cycling (Operating Control) Pressure Switch

34 Pressure Switches

Differential Air Pressure Switch

SPST Closes on Rise (Differential)

Differential Refrigerant Pressure SPST Opens on Rise (Differential) Switch

35 Pressure Switches THE CONTACTS OF A SAFETY CONTROL ARE DRAWN IN THE NORMAL RUN POSITION, USUALLY CLOSED

36 Temperature Switches

SPST Closes on Drop (Operating Control) Heating Defrost Thermostat Thermostat

SPST Closes on Rise (Operating Control) Return Water Cooling Thermostat Temperature Controller

37 Temperature Switches

SPST Opens on Rise (Safety Control) Overtemperature Discharge Gas Limit Switch Thermostat

SPST Opens on Drop (Safety Control) Freeze Protection Thermostat

38 Temperature Switches

SPDT Temperature (Safety or Operating)

Low-Water Temperature Cutout Control

Klixonâ Bi-Metal Temperature Overtemperature (Safety) Cutout Control

39 Temperature Switches THE CONTACTS OF AN OPERATING CONTROL ARE DRAWN OPEN, WITH NO CALL FOR COOLING, HEATING

40 Humidity Control

SPST Humidistat Closes on Drop (Operating Control)

SPST De-Humidistat Closes on Rise (Operating Control)

41 Time Delay

Time Delay Relay Delays Closing Time Delay Relay (Mechanical/Thermal) (Electronic) (Electronic)

Time Delay Relay Time Delay Relay (Mechanical) Delays Opening (Mechanical/Thermal) (Electronic) Time Delay Relay (Thermal) 42 Time Delay

THE CONTACTS OF A TIMER ARE DRAWN IN THE READY-TO-START POSITION OR AT TIME ZERO ON A BAR CYCLE DIAGRAM

NOTE: BLACK DENOTES CLOSED CIRCUITS

43 Manual Switches

SPST Normally Open Manually Operated Push Button

SPST Normally Closed Manually Operated Momentary Push Button Push Button

SPDT Switch Single-Pole Double-Throw Switch 44 Flow Switches

Flow Switch

SPST Flow Switch Opens on Rise (Safety Control)

Sail Switch

SPST Flow Switch Closes on Rise (Safety and Operating) Thermal Dispersion

Flow Switches 45 Enthalpy Switches

Electronic Enthalpy Control

SPDT Enthalpy Control (Operating Control)

Mechanical Enthalpy Control 46 Capacitors Run Capacitor

Run Capacitor (Marked Terminal) Dual Run Capacitor

Start Start Capacitor Capacitor

47 Fuses

One Time Fuse (Fusible Link)

Fuse - Fusible Link One Time Fuse

48 Transformers

49 230 VAC

24 VAC Fused & Non Fused Secondary

COMM NF F

24 VAC

Multi Tap Primary

575 480 380 230 200 C

50 Dual Secondary Transformer

Dual Secondary With Center Tapped Transformer

51 Transformers

Secondary Volt Amps Voltage

VA RATING TOTAL AMP DRAW OF A CIRCUIT = SECONDARY VOLTAGE 75VA = = 3.1 AMPS 24V 52