What an HVAC Technician Checks During a Tune Up

Cooling System Tune Up (Spring Visit)

Refrigerant pressure check. The technician connects manifold gauges to the service valves on the refrigerant lines and measures the system pressures on both the high side (discharge) and low side (suction). These pressures are compared against the manufacturer specifications for your system at the current outdoor temperature. Incorrect pressures indicate a refrigerant leak, an overcharge from a previous service visit, or a metering device problem. This single test is the most reliable indicator of whether the cooling system will perform at rated capacity.

Evaporator coil inspection. The technician opens the air handler cabinet to visually inspect the evaporator coil for dirt, biofilm, mold, and physical damage. A dirty evaporator reduces heat absorption and can cause the coil temperature to drop below freezing, leading to ice formation. If the coil is dirty, the technician either cleans it during the visit or recommends a separate deep-cleaning appointment.

Condenser coil inspection and cleaning. The outdoor condenser coil is checked for dirt, bent fins, and debris accumulation. The technician may rinse the coil with a hose or apply a commercial coil cleaner for heavier buildup. Condenser capacity depends entirely on airflow through the fins, so even a thin layer of grime affects performance measurably.

Condensate drain line check. The technician verifies the drain line is flowing freely by checking for water at the outdoor termination while the system runs. If the line is slow or clogged, it is flushed during the visit. The drain pan is inspected for standing water, corrosion, cracks, and biological growth.

Electrical testing. Using a multimeter and clamp meter, the technician measures voltage at the disconnect and the contactor, tests capacitor strength in microfarads against rated values, checks contactor contacts for pitting and wear, measures motor amperage against the rated full load amps listed on the motor nameplate, and inspects all wiring connections for tightness and signs of heat damage. A weak capacitor or a loose connection caught during a tune up prevents the emergency failure that would result if left unaddressed.

Thermostat calibration. The technician verifies the thermostat temperature reading against a calibrated thermometer and adjusts the calibration offset if the readings differ by more than two degrees. The cooling cycle operation is tested to confirm the system responds properly to thermostat commands and shuts off at the correct temperature.

Airflow measurement. The temperature split between the return air and supply air is measured. A properly operating system produces a 15 to 22 degree Fahrenheit temperature drop across the evaporator coil. A smaller split indicates low refrigerant, a dirty coil, or excessive airflow. A larger split indicates restricted airflow, a clogged filter, or closed supply registers.

Heating System Tune Up (Fall Visit)

Heat exchanger inspection. This is the most critical safety check in the entire tune up. The technician inspects the heat exchanger cells for cracks, rust holes, and separation at the seams using a mirror, camera, or visual inspection through the burner openings. A cracked heat exchanger can leak carbon monoxide into the airstream. If a crack is found, the technician should shut down the furnace immediately and recommend either heat exchanger replacement (if under warranty) or full furnace replacement (if the warranty has expired).

Burner inspection and cleaning. The burners are removed or accessed and inspected for carbon buildup, rust, and corrosion. The technician checks the flame pattern, which should be a steady blue flame with slight yellow tips across all burners. An uneven flame, a lazy yellow flame, or delayed ignition indicates dirt, gas pressure problems, or a cracked heat exchanger affecting combustion airflow.

Flame sensor inspection. The flame sensor is a small metal rod that sits in the burner flame and sends a signal to the control board confirming that the gas valve should remain open. A dirty flame sensor cannot detect the flame, causing the control board to shut down the gas valve as a safety measure. The technician either cleans the sensor with fine emery cloth or replaces it if it is heavily corroded. This is the most common cause of furnace ignition failure and one of the simplest repairs in the HVAC trade.

Ignition system test. Whether your furnace uses a hot surface igniter, an intermittent pilot, or a standing pilot, the technician tests the ignition sequence from the thermostat call through burner light. The hot surface igniter (the most common type in modern furnaces) is checked for cracks, as a cracked igniter can work intermittently before failing completely during the coldest weather. Igniter replacement costs $80 to $200, and catching a failing igniter during the tune up prevents the no-heat emergency call that would cost double or more.

Gas pressure measurement. The technician measures gas pressure at the manifold with a manometer and compares it to the manufacturer specification printed on the furnace rating plate. Gas pressure that is too high causes the furnace to overheat and can damage the heat exchanger. Gas pressure that is too low produces incomplete combustion, generates carbon monoxide, and reduces heating output. Adjustment requires setting the gas valve regulator, which is a professional-only task.

Flue and venting inspection. The technician inspects the flue pipe connections for tightness and proper slope, checks the draft with the furnace running, and looks for signs of backdrafting (soot marks around the draft hood or barometric damper). Proper venting is essential for removing combustion byproducts from your home. A blocked or disconnected flue can cause carbon monoxide to spill into the living space.

Safety control testing. The high-limit switch, pressure switch, and rollout switch are tested to verify they will shut down the furnace if unsafe conditions are detected. These switches are the safety net that prevents overheating, combustion gas spillage, and flame rollout. A faulty safety switch that fails to trip when needed creates a fire or CO hazard.

Blower motor assessment. The technician measures blower motor amperage, checks for unusual noise or vibration, inspects the blower wheel for dirt accumulation and balance, and lubricates the motor bearings if the motor has accessible lubrication ports. A dirty blower wheel can reduce airflow by 20 percent or more, and an unbalanced wheel creates vibration that wears out the motor bearings prematurely.

What to Expect After the Visit

A thorough technician provides a written report at the end of the visit that summarizes the findings, notes any components that are showing wear or approaching failure, and recommends any repairs or follow-up work. This report is your documentation for warranty purposes and your reference point for future maintenance comparisons. If the technician completes the visit in less than 30 minutes, does not use a multimeter, does not open the electrical compartment, or cannot tell you what the heat exchanger looks like, the inspection was not thorough.

Repair recommendations should be prioritized as safety critical (do immediately), performance affecting (schedule soon), or advisory (monitor and address in the future). A reputable technician explains the finding, the risk of leaving it unaddressed, the cost to fix it, and the timeline for when it needs attention. Be cautious of any technician who presents every finding as an urgent emergency or who recommends replacing equipment that a competent technician could repair.

Keep the report and any invoices in your maintenance log for warranty documentation and future reference. If you switch HVAC companies, the next technician benefits from seeing what was inspected and noted during previous visits. Over time, these reports create a history that reveals trends in your system's condition, helps predict upcoming replacement needs, and provides evidence of proper maintenance if you file a warranty claim or sell the home.