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HVAC Electrical Symbols Chart

Plain-language descriptions of the symbols most often found on HVAC wiring and ladder diagrams. Symbols vary by maker, so the legend on the unit's diagram always governs.

Ref HV-0050IEEE 315

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

HVAC wiring diagrams use graphic symbols for switches, coils, motors and other parts. Many are based on IEEE 315 (ANSI Y32.2), but each equipment maker adds its own. Most units carry two drawings: a connection (pictorial) diagram that shows where wires land, and a ladder (schematic) diagram that shows how the circuit works. This chart describes the common symbols in words.

How to read it

Start with the legend on the unit's diagram. It defines the abbreviations (such as CC, IFR, LPS) and line types.
Read the ladder diagram from the left rail (power) to the right rail (common), one rung at a time.
Contacts are drawn in their de-energized or shelf state.
Contacts that belong to a coil carry the same label as the coil.

Symbol chart

Symbol (as drawn)	Meaning	Common labels
Two short parallel lines across the wire	Normally open (NO) contact	CC, R, IFR
Two parallel lines with a diagonal slash	Normally closed (NC) contact	CR, R
Circle with letters inside	Relay or contactor coil	CC, CR, IFR
Two coils side by side with a line between	Transformer	TRANS
Circle with M or a motor label	Motor	IFM, OFM, COMP
Two parallel lines, one curved	Capacitor	CAP, RC, SC
Zigzag line	Resistor or heater	HTR, CH
Small rectangle or S-curve in line	Fuse	FU
Switch blade with a diaphragm or bellows	Pressure switch	HPS, LPS
Switch blade with a wavy or thermal element	Temperature switch or overload	TS, OL, LS
Lines fanning down to a point	Ground	GND
Dashed line	Field wiring, or a mechanical link between parts (see legend)	—
Solid dot at a crossing	Wires connected	—

Key points

Field wiring vs factory wiring: Many makers draw factory wiring solid and field wiring dashed. Others use the opposite or a different color. Check the legend.
A crossing with no dot usually means the wires cross without connecting.
The same symbol can mean different parts on different brands. Use the parts list to confirm.
Safety controls are usually drawn in series with the coil they protect.

Common mistakes

Reading NC contacts as open because the unit is off.
Assuming all dashed lines are field wiring.
Using a symbol chart from one brand to troubleshoot another without reading its legend.

Governing standards: IEEE 315 (graphic symbols for electrical diagrams); the equipment manufacturer's wiring diagram and legend.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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