Oklahoma HVACR Journeyman Unlimited

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

Both use electromagnetic coils and can be rebuilt, but the motor starter's distinguishing feature is built-in overload protection that prevents motors from burning out or overheating.

A weight-operated current relay must be mounted in a level position, whereas a current relay using a rotary solenoid can be mounted in any position.

An SSR switches circuits with electronic components (transistors, SCRs, triacs) and has no physical movement of mechanical parts, and is typically used to start single-phase motors; electromagnetic relays switch mechanically.

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 reset, while a soft lockout automatically retries after a waiting period.

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

K-value is heat passing through one square foot of material one inch thick in one hour per 1°F 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.

The subcooling method is used to check charge on systems with thermostatic expansion valves (low subcooling suggests undercharge, high suggests overcharge), while the superheat method is used on fixed-orifice systems such as capillary tubes.

Turning the range screw clockwise raises both cut-in and cut-out an equal amount (differential unchanged), while the differential adjustment turned clockwise raises only the cut-out pressure and does not affect cut-in.

Three-phase supply is already phase-split so the motor develops starting torque without start windings or capacitors, and delivers constant power because there is never an instant when all voltages are zero; single-phase motors need start components.

In an HSI system the glow coil only ignites and cannot sense flame; a separate flame rod performs flame rectification sensing, and if it is dirty or oxidized the module closes the gas valve seconds after ignition (HSI systems use no thermocouple).

Recovering at the liquid line takes refrigerant as subcooled liquid (after the condenser), which speeds recovery, while the discharge service valve delivers superheated high-pressure vapor, making recovery slower and less efficient.

A radial system runs individual branch ducts directly from the central plenum to each outlet with no trunk line, while a perimeter loop system (used with downflow furnaces in slab homes without basements) has branches feeding a perimeter duct cast in the slab.

Per IMC 603.2, Manual D is an accepted duct-sizing method for a single dwelling unit (along with manufacturer's instructions or other approved methods); Manual J is for load calculations and Manual S is for equipment selection, and the ASHRAE Handbook of Fundamentals is required for buildings other than single dwelling units.