HVAC Maintenance Checklist

The data plate carries all of it, and a wash-down tends to render that plate illegible before anything else on the machine. Serial and model are what a Supplier goes by when selling the right part, while refrigerant type settles which gauges leave the truck.

A meter across the terminals is the proof; the handle position on its own is not. Wear inside a disconnect can leave a leg live while the handle reads off, and a rooftop unit is often fed from a panel nobody on site can locate.

Solid footing and an escape route matter before any panel comes off. Anything outside your scope — spongy roof decking, an absent guard rail, pooled water — still belongs in the writeup, so it is worth catching now.

About half an inch of deflection at the midpoint of the span is the target. Over-tightening destroys bearings quicker than a slack belt does, and a wheel with dirt packed between its blades shifts noticeably less air on the same current draw.

Even a healthy belt is worth recording. That number is stamped into the belt and wears away long before the belt itself gives up, which is how a ten-minute swap turns into a return trip.

Size and quantity belong in the notes alongside condition. Restriction here is the leading reason behind a no-cooling call and it skews every reading taken afterward, so the swap comes before any measurement.

Sitting outside the filter rack, this screen is usually the one part nobody has touched. Blocked, it holds the economizer on mechanical cooling in weather that should be running on outside air — something that surfaces on the bill rather than as a complaint.

Dirt gathers on the upstream face, not the side that is easy to reach. Ice on the coil at the time of the visit makes every reading meaningless until it has thawed, so a second look later beats pressures taken across ice.

If the drain is on the suction side of the fan, an empty trap pulls in air instead of water. The pan then overflows even though nothing is blocking the drain line. The trap wants refilling once flushed, and the pan has to slope toward its outlet.

The display tells you less than an actual call for cooling and then for heat. Wrong mode, or a position above a supply register, is often the whole reason for the complaint that generated the call.

Discoloration and lug torque are the two things worth attention. Scorching around a contactor terminal is evidence of arcing, and that joint will fail again within a few cycles no matter how good it reads today.

With the power off it should turn freely by hand, and running it should not produce bearing noise. Too hot to keep a hand on after a short run means the motor is finished even while it still turns.

Hail damage or a split hub unbalances the fan, and that vibration eventually claims the motor bearings. Blade height inside the shroud counts too — a setscrew that has crept quietly costs a surprising amount of airflow.

Washing from the inside out sends dirt back out the way it arrived. Bent fins want straightening and anything crowding the unit — shrubs, a fence, a dryer vent — wants clearing, because head pressure tracks airflow through this coil above all else.

Any temperature drop you can measure across it says the dryer is restricted and due for replacement. Worth noting if none is fitted at all: a system opened for a repair and closed without a fresh dryer keeps throwing moisture-related failures.

The crankcase heater is what stops refrigerant migrating into the oil during the off cycle, so it has to be working. Flooded starts kill a compressor slowly, and testing a heater costs almost nothing.

One filter covers both seasons, making this a second look rather than duplication. Restriction during heating drives supply temperature up and short-cycles the unit on its high limit, which presents as an intermittent fault.

Use a light and a mirror to look for cracks, rust and seams that have opened. If anything looks wrong, red-tag the unit rather than writing a note. A cracked heat exchanger lets exhaust gas, including carbon monoxide, into the air people breathe. This is a safety item, not a maintenance item.

Burners want to be seated square with the flame travelling cleanly across them, neither lifting nor rolling out. Soot found anywhere on the assembly means the combustion side has to be sorted before the unit returns to service.

Joints you have disturbed and any showing corrosion want a leak check, and the manual shutoff has to sit somewhere a person could actually get to it. Whether the valve holds tight with the unit off is something to test, not assume.

The inducer has to build enough pressure to close the pressure switch before the gas valve will open. If the inducer is weak, the unit tries to light and then stops. The usual causes are dirt on the wheel or water in the pressure tubing. Water in the tubing is the more common of the two.

Ports open up once scale and rust come off the burners, and the flame pattern across all of them tells the rest of the story once lit. Yellow tips or an uneven flame indicate either a plugged port or a shortage of combustion air.

The diagnostic light's fault history is the only account of what the unit has done between visits, so it is worth reading before it gets cleared. Flame-sensor cleanliness matters here too, being the commonest reason a board that is otherwise fine locks out.

A heat call has to carry the sequence all the way through in the right order, staging included. Wire a thermostat for the wrong system type and the heat looks fine on a mild day, then falls behind when it turns cold.

Terminals on the combustion side see more heat cycling than the cooling side and work loose sooner. Grounding deserves the same attention, because flame rectification depends on a solid ground and a poor one throws intermittent lockouts that mimic a failing sensor.