MANUAL SWITCHES & CONTROLS
The simplest manual disconnect switch on a schematic, abbreviated SPST (#8).
What is a Single Pole Single Throw Switch?
A safety switch symbol configured to open its contacts when system pressure exceeds a set limit (#14).
What is a High Pressure Switch (Open on Rise)?
: Represented by two parallel plates (one straight, one curved) used for phase-shifting and starting torque (#1).
What is a Capacitor?
Represented by two parallel open lines on a diagram, remaining non-conductive until the associated coil is energized (#16).
What are Normally Open (N.O.) Contacts?
A meter symbol with a circled "V" used to measure potential difference across two points in a live circuit (#33).
What is a Voltmeter?
This switch controls one input circuit but toggles power between two alternative outputs (#9).
What is a Single Pole Double Throw (SPDT) Switch?
A thermostat contact symbol configured to close on temperature rise to call for mechanical cooling (#23).
What is a Cooling Thermostat (Close on Rise)?
This electric load uses a zigzag resistor symbol and is wrapped around the bottom of a compressor to boil off liquid refrigerant during the off-cycle (#30).
What is a Crankcase Heater?
A component symbol with primary and secondary windings used to step 120V or 240V line voltage down to 24V control voltage (#39).
What is a 2-Pole Contactor?
A meter symbol with a circled "A" wired in series or clamped around a conductor to measure circuit current (#31).
What is an Ammeter?
A manual momentary switch symbol designed to open the circuit only while depressed (#12).
What is a Push Button Off Switch?
A thermostat contact symbol designed to open when the temperature rises past the setpoint, cutting off heat (#24).
What is a Heating Thermostat (Open on Rise)?
An electromechanical output load consisting of a coiled wire and movable plunger, shown as symbol #18
What is a Solenoid?
A contactor symbol featuring two sets of heavy-duty contacts controlled by a single magnetic coil (#45).
What is a 2-Pole Contactor?
A temperature sensor symbol consisting of two dissimilar metal wires joined at one end that generates millivolts when heated (#42).
What is a Thermocouple?
A switch designed to simultaneously open or close two separate isolated lines, abbreviated DPST (#10).
What is a Double Pole Single Throw Switch?
A pressure switch symbol that makes contact as refrigerant pressure increases to establish a minimum operating pressure (#15).
What is a Low Pressure Switch (Close on Rise)?
A motor circle symbol with designations indicating operation from three hot electrical lines (#48).
What is a 3-Phase Motor?
The switching device symbol shown as #43 that uses an electromagnetic coil to pull in internal mechanical contacts.
What is a Magnetic Relay?
A solid-state temperature-sensing resistor symbol whose resistance changes predictably with temperature (#41).
What is a Thermistor?
This symbol shows two parallel poles that simultaneously redirect two distinct lines between two sets of output terminals (#11).
What is a Double Pole Double Throw (DPDT) Switch?
A safety device symbol that uses two bonded dissimilar metals to warp and open contacts during motor overcurrent or high temperature (#20).
: What is a Bimetal Overload Switch?
A single-use thermal safety load symbol designed to melt physically and permanently open the circuit during extreme over-temperature events (#40)
What is a Fusible Link?
This assembly combines a small timing motor and mechanical switch contacts to regulate periodic sequences like defrost (#19).
What is a Timer Switch & Motor?
An electronic semiconductor symbol used to convert alternating current (AC) into direct current (DC) for control boards (#22).
What is a Rectifier?