Mississippi Residential HVAC

A pictorial diagram shows the approximate physical location of devices and may show wire colors, while a ladder diagram shows the order of component operation using horizontal rungs between two vertical power lines.

When cool, the PTC thermistor has low resistance (3–12 Ω) and carries startup current; once heated to its set point, resistance rises dramatically (10–20 kΩ), forcing current through the run capacitor instead.

An SSR switches circuits using electronic components (transistors, SCRs, triacs) with no mechanical movement, whereas an electromagnetic relay uses physical mechanical parts to open or close contacts.

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 identifiable illness or specific cause and its symptoms resolve once occupants leave.

K-value measures heat flow through a standardized one-inch thickness of material per square foot per hour per 1°F difference, while C-value measures thermal conductance based on the material's actual measured thickness.

ACR tubing is sized by its actual outside diameter, whereas copper water tubing nominal size equals the actual outside diameter minus 1/8 inch.

Galvanized pipe is coated with zinc for corrosion resistance and is used primarily in water systems, while black pipe has no zinc coating and is used for gas lines and non-water applications.

Time-terminated defrost runs for a fixed preset duration regardless of actual coil condition, while temperature-terminated defrost ends the cycle when a sensor on the coil reaches a set temperature confirming frost has melted.

The glow coil is used only for ignition and cannot sense a flame, while the flame rod uses flame rectification to send a microamp signal back to the ignition control module to confirm burner flame presence.

Arc-resistant-jacketed CSST is considered bonded when connected to a properly grounded appliance and requires no separate bonding jumper, while standard CSST requires a bonding jumper of not less than 6 AWG copper wire connected to the grounding electrode system.

A pilot-operated reversing valve uses a solenoid pilot valve and capillary tubes to harness the suction-to-discharge pressure difference to shift the piston, while a direct-acting reversing valve uses direct mechanical action of the solenoid plunger and is used in smaller systems.

A system with volume less than 10 cubic feet or in a single-family dwelling requires a minimum test duration of 10 minutes, and in all cases test pressure must not be less than 3 psig regardless of design pressure.