Tennessee CMC-C Mechanical HVAC/Refrigeration Contractor

A pictorial diagram shows all connections plus the approximate physical location of devices in the unit (and may show wire colors), while a ladder diagram shows the order of component operation as horizontal rungs (individual circuits with loads and controls) between two vertical power lines.

K-value is heat passing through one square foot of material one inch thick in one hour at a 1°F temperature difference (Btu·in/hr·ft²·°F), while C-value is based on the material's actual measured thickness rather than a standardized 1-inch thickness.

BRI is a specifically diagnosable illness caused by exposure to airborne agents whose symptoms do NOT disappear when the occupant leaves, while SBS has no specific cause or identifiable illness and its symptoms disappear when occupants leave the building.

ACR tubing is designated by its actual outside diameter, while copper water tubing nominal size equals the outside diameter minus 1/8″.

Galvanized pipe is treated with a zinc anticorrosion material and is used primarily in water systems to prevent rust, while black pipe is usually less expensive and is used for gas lines and applications that do not carry water.

A hard lockout shuts the system down for an unspecified time after a failed trial for ignition and requires a service call or power interruption to the ignition control module to reset, while a soft lockout automatically retries after a waiting period.

The subcooling method is generally used to check charge on systems with thermostatic expansion valves, while the superheat method is used on systems with fixed orifice metering devices such as capillary tubes.

An SSR switches circuits with electronic components (transistors, SCRs, triacs) and has no physical movement of mechanical parts, while an electromagnetic relay switches through mechanical contacts; SSRs are typically used to start single-phase motors.

Three-phase supply is already phase-split so the motor develops starting torque without start windings or capacitors, and delivers constant power because the voltages never all reach zero at the same instant; single-phase motors need start windings/capacitors for phase splitting.

Per IFGC 2021 Section 305.5, appliances in private garages require a minimum 6 ft clearance above the floor while public garages require 8 ft; an exception applies where the appliance is protected from motor vehicle impact and installed per Section 305.3.

Per the IECC, maximum leakage is 3 cfm per 100 ft² of conditioned space when tested before the air handler is installed, versus 4 cfm per 100 ft² when tested with the air handler installed.

A vertical riser is sized smaller in diameter than the horizontal run because oil return requires 1,000–1,500 fpm in the riser versus only 500–700 fpm in horizontal runs.

At the liquid line the refrigerant is already subcooled liquid, which speeds recovery, while at the discharge service valve it is superheated high-pressure vapor, making recovery slower and less efficient.

A liquid line restriction gives low suction pressure, low head pressure, high superheat and normal subcooling, while an inefficient compressor gives HIGH suction pressure with LOW head pressure.