Texas HVAC Contractor Course Notes

Air Distribution is the largest Environmental Air Class A domain (18 of 120 scored items). Work from design airflow to measured airflow: load calculation establishes room demand, equipment selection establishes available airflow and pressure, Manual D-style duct design accounts for friction and fitting equivalent length, and balancing verifies delivery. Diagnose low airflow by measuring total external static pressure and component pressure drops rather than guessing from room temperature. Filters, coils, dampers, undersized ducts, return restrictions, leakage, and closed-door return-path problems can all move the blower away from its rated operating point.

• Adding refrigerant or replacing a blower before correcting a known airflow restriction.

• Read the blower-table reference point carefully: a higher measured external static generally means less airflow at the same blower setting.

Equipment Requirements and Design is 14 of 120 scored items. Separate sensible load (temperature) from latent load (moisture), use building-specific load inputs, then select equipment from performance data rather than nominal tonnage or square-foot rules. Design changes such as west glass, occupancy, outdoor-air requirements, insulation, infiltration, and moving ducts into a vented attic can materially change load. Electrical design questions require reading nameplates and diagrams, checking voltage under load, and distinguishing an upstream supply problem from a unit fault. Code questions require the adopted jurisdictional requirements plus applicable listing/manufacturer instructions.

• Treating sensible and latent load as interchangeable.

• Write SHR as S/T and remember total = sensible + latent.

Service is 12 of 120 scored items and rewards a disciplined diagnostic sequence. Confirm the complaint, identify the equipment/refrigerant, inspect for hazards and obvious defects, establish stable operating conditions, follow the wiring/refrigeration sequence, measure defined test points, compare results with approved data, repair the demonstrated cause, and verify full operation. Never diagnose charge from one pressure. Superheat is actual vapor temperature minus saturation temperature at the same pressure/location; subcooling is saturation temperature minus actual liquid temperature at the specified liquid-line location. EPA Section 608 recovery requirements vary by appliance/refrigerant conditions and include limited evacuation exceptions for leaking equipment.

• Adding refrigerant because suction pressure is low.

• Calculate first, interpret second: SH = actual vapor − saturation; SC = saturation − actual liquid.

Testing is 12 of 120 scored items. Select the test that directly measures the suspected condition and perform it under safe, meaningful operating conditions. Air-side examples include delivered CFM, total external static pressure, and component pressure drop. Electrical testing may require energized voltage/current measurements when deenergized testing cannot reveal the fault, but such work is for qualified persons using appropriate work practices, PPE, and properly rated instruments. Combustion and gas testing must reflect actual operating load, code requirements, and manufacturer data rather than arbitrary adjustment.

• Using room temperature to diagnose filter resistance.

• Direct measurement beats inference when the question gives access to a test point.

HVAC Systems is 11 of 120 scored items. Understand component function, installation compliance, startup/commissioning, and refrigeration-system behavior. The compressor creates pressure difference and moves vapor, the condenser rejects heat and condenses refrigerant, the metering device creates the controlled pressure drop and meters flow, and the evaporator absorbs heat and boils refrigerant. Installation questions emphasize approved drainage, listed clearances, current instructions, and final operational verification. Diagnosis questions require correcting air-side or heat-rejection defects before interpreting refrigerant charge.

• Replacing a metering device because of low airflow.

• Trace the refrigerant path before naming a failed component.

Basic Refrigeration Components is 6 of 120 scored items. Diagnose components by their function in the cycle and corroborating measurements, not one pressure reading. Weak compressor pumping is supported by inadequate pressure differential after external causes are ruled out. Condenser performance depends on heat rejection, so verify air or water flow and temperature change before altering charge. Evaporator starvation, uneven frost, or abnormal superheat can point toward refrigerant feed/distribution after airflow and load are confirmed. Metering-device diagnosis includes sensing, control, wiring, restrictions, and commanded position for electronic valves.

• Condemning a compressor from close pressures without eliminating external causes.

• Ask what the component is supposed to do, then choose the measurement that directly tests that function.

Combustion Air is 6 of 120 scored items. The exam emphasizes whether the appliance has a reliable air path under actual building conditions. Natural-draft appliances that spill only when exhaust fans run point to building depressurization/combustion-air interaction. Direct-vent appliances depend on their dedicated intake/vent terminations, so recent landscaping or blockage is a high-value first check. Do not compensate for inadequate combustion air by changing burner input, inducer settings, or vent dimensions outside approved instructions.

• Changing vent size before investigating building depressurization.

• Look for what changed: exhaust fan operation, landscaping, closed doors, or blocked openings.

Controls is 6 of 120 scored items. Follow the control sequence from initiating input through safeties, logic, outputs, loads and feedback. A disagreement between measured process pressure/temperature and a safety switch state calls for testing the sensing/control path: setpoint, tubing, wiring, sensor calibration and switch operation. Safety devices are not permanent troubleshooting jumpers. Temporary bypassing is only for an authorized controlled test when appropriate, followed by restoration and verification of protection before normal service.

• Replacing a control without verifying its input and wiring.

• Follow the schematic in order; don't jump randomly among components.

Piping is 6 of 120 scored items. Match material, size, fittings, supports and valves to the fluid/refrigerant, pressure, temperature, compatibility and system function. Condensate drains need approved material, minimum sizing, continuous drainage slope, required trap/vent arrangements and approved disposal; the drain should not be reduced below the code-required size downstream. Refrigerant line sizing is a tradeoff among pressure drop, velocity, oil return, capacity and operating range — larger is not automatically better. Hydronic serviceability requires intentional isolation, not merely a check valve or stopped pump.

• Reducing condensate pipe because the downstream section is steeper.

• First identify the fluid and function; then size/material/support/valve requirements become easier.

Refrigeration Principles is 6 of 120 scored items. Use pressure-temperature relationships to determine saturation state, then calculate superheat or subcooling at the correct location. Heat moves because of temperature difference; the refrigeration cycle creates conditions that absorb heat at the evaporator and reject it at the condenser. System pressure is contextual: refrigerant identity, indoor/outdoor load, airflow or water flow, and component condition all matter. A pressure value by itself does not prove charge or component failure.

• Reversing the superheat or subcooling subtraction.

• Write the equations before doing the arithmetic.

Safety is 6 of 120 scored items. The default electrical strategy is to deenergize and establish an electrically safe work condition before employees work on or near exposed parts. Verify absence of voltage with properly rated equipment before treating conductors as deenergized. Some diagnostics require energized measurement because the condition cannot be determined deenergized; those tasks require qualified persons, appropriate PPE/work practices and instruments rated for the circuit. Refrigerant safety includes identifying the refrigerant, controlling pressure/energy hazards, using compliant recovery practices and never leaving required safeties defeated.

• Assuming a locked disconnect proves zero voltage without verification.

• Distinguish 'test for absence of voltage' from 'measure an energized operating voltage' — both can be correct in different stages of the task.

Texas Laws and Rules is 6 of 120 scored items. For Environmental Air Class A, know the TDLR license class, endorsement scope, supervision and business-compliance requirements. Class A permits work on any size unit; Class B is limited to cooling systems of 25 tons and under and heating systems of 1.5 million Btu/h and under. Environmental Air Conditioning covers treating air for human comfort by controlling temperature, humidity, cleanliness, ventilation and circulation. Current TDLR Class A liability minimums are $300,000 per occurrence, $600,000 aggregate bodily injury/property damage, and $300,000 products/completed operations. Contractor licenses are one year and renewal requires 8 approved CE hours, including 1 hour of Texas law/rules.

• Believing the Environmental Air endorsement removes Class B size limits.

• Class A = no unit-size limit; Class B = 25 tons cooling / 1.5M Btu/h heating ceiling.

Ventilation is 6 of 120 scored items. Evaluate outdoor air as both a total-system quantity and a zone-distribution requirement. Correct total outdoor airflow does not prove each occupied zone receives its design share; balancing and distribution must be verified. Machinery-room questions focus on code-required ventilation to outdoors and the difference between normal and emergency exhaust/control modes. Commissioning should demonstrate the actual control sequence rather than assume emergency operation will occur.

• Closing outdoor-air dampers and relying on infiltration.

• Separate quantity from distribution: 'how much total?' and 'where does it go?' are different questions.

Venting is 5 of 120 scored items. For clothes dryers, verify an independent, unobstructed exhaust path to outdoors and apply the code/manufacturer requirements; screens at the termination are prohibited under the IRC provisions used by the bank because lint accumulation restricts flow. For fuel-fired appliances, a separated/corroded vent or draft-hood spillage is a safety issue, not something to mask by increasing firing rate. When spillage begins only with a large exhaust fan, investigate building depressurization, combustion air and vent performance together.

• Increasing dryer heat instead of clearing a lint restriction.

• For venting questions, first identify appliance type and whether the problem is restriction, physical vent integrity or building-pressure interaction.