Seasonal HVAC Maintenance Guide
A working tech's checklist for what to verify heading into cooling season and heating season — with the target numbers that turn a "looks fine" visit into a documented, callback-proof tune-up.
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In This Guide
Why Seasonal Maintenance Pays Off
A seasonal maintenance visit is the cheapest diagnostic call a customer will ever pay for. The whole point is to catch the failure before the 98°F Saturday when the system locks out on high head pressure. Two visits a year — one in spring before cooling season and one in fall before heating season — cover the two hardest transitions on the equipment.
The mistake techs make is treating a tune-up as a wipe-down. A real PM is a set of measured readings compared against target ranges. A weak run capacitor still spins the fan on a mild day but drops out under load in July. A condenser coil packed with cottonwood adds 40–60 psi of head pressure that the homeowner never notices until efficiency craters. You find those by measuring, not by looking.
The two big transitions
Spring / cooling season: airflow, condenser coil, capacitor, and refrigerant charge take the heat. Fall / heating season: ignition, flame sensor, heat exchanger, and combustion safeties are the priority. Some checks — filter, static pressure, wiring, condensate — belong in every visit.
Before You Start: Safety First
Every seasonal PM starts the same way, regardless of the season:
- Kill power at the disconnect before removing panels — the condenser disconnect and the furnace switch, not just the thermostat.
- Discharge capacitors with an insulated resistor before probing. A charged 45/5 dual-run cap will bite.
- Verify EPA 608 handling. Any time you break into the refrigerant circuit, recovery is required — venting is a federal violation under Section 608.
- Respect A2L equipment. On R-32 and R-454B systems, follow the manufacturer's ignition-source and leak-detection procedures; these refrigerants are mildly flammable (ASHRAE 34 class A2L).
- Treat gas as gas. On the heating side, smell and sniff for leaks, and never bypass a rollout or limit switch to "get it running."
Cooling-Season Checklist (Spring)
Head into cooling season with airflow first — most refrigerant-side symptoms are actually airflow problems wearing a disguise. Work the list in this order:
- Filter. Replace or clean it. A loaded filter is the single most common cause of low airflow, frozen coils, and high head pressure.
- Evaporator coil & blower. Inspect for dirt and biofilm. A dirty evaporator raises static pressure and starves airflow; a dirty blower wheel can cut CFM by 20% or more.
- Condensate drain. Flush the line, confirm the trap holds water, and test the float switch. Algae clogs are the top cause of nuisance shutdowns and ceiling stains.
- Condenser coil. Wash from the inside out with a coil cleaner. Spring debris and cottonwood are the classic cause of high head pressure after winter.
- Capacitor. Read microfarads with a meter and compare to the nameplate — a cap that has drifted below about 90% of rated µF is on its way out.
- Contactor. Inspect the points for pitting or welding; arcing contacts drop voltage to the compressor and cause hard starts.
- Electrical connections. Check for discoloration and torque lugs to spec. Loose connections are a heat source and a callback waiting to happen.
- Refrigerant charge. Verify by superheat (fixed orifice) or subcooling (TXV) — not by topping off on pressure alone. See the target ranges below.
- Temperature split. Once it's running steady, measure return and supply air to confirm the system is actually moving heat.
Field tip: don't chase pressure
If suction is low and superheat is high, the reflex is to add refrigerant. Check the filter and coil first. Low airflow mimics an undercharge — you can end up overcharging a system that only needed a clean filter, and then it slugs the compressor on the next humid day.
Target Numbers for Cooling
A tune-up is only credible if you write down readings and compare them to targets. These are the field ranges to carry into cooling season:
| Measurement | Target Range | What It Tells You |
|---|---|---|
| Temperature split (ΔT) | 14–22°F | Overall cooling performance |
| Superheat (TXV) | 8–14°F | Evaporator feed / charge |
| Subcooling (TXV) | 10–18°F | System charge (per nameplate) |
| Total external static pressure | ≤ 0.50 iwc | Duct / filter restriction |
| Airflow | ~400 CFM/ton | Blower delivering rated flow |
| Run capacitor | ≥ 90% of rated µF | Motor / compressor start health |
Superheat and subcooling
Superheat = suction line temp − evaporator saturation temp. Subcooling = condenser saturation temp − liquid line temp. On a fixed-orifice system, charge to target superheat; on a TXV system, charge to subcooling. Always confirm the manufacturer's target on the nameplate before you commit a reading.
Static pressure is your airflow proxy
If you only own a manometer and not a flow hood, total external static pressure is your fast airflow check. Anything much above 0.50 iwc on a residential system points to a dirty filter, undersized ductwork, or a restricted coil — diagnose it before you touch the charge.
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Heating-Season Checklist (Fall)
Come fall, the priority shifts from refrigerant and coils to combustion and ignition. On a gas furnace, work the list in this order:
- Filter and airflow. Same as spring — a restricted filter trips the high-limit and short-cycles the furnace.
- Flame sensor. Pull it and clean the rod with a fine abrasive pad. A dirty flame sensor is the single most common no-heat call, full stop.
- Igniter. Inspect the hot-surface igniter for cracks and check resistance; a spark igniter should have a clean, consistent gap.
- Heat exchanger. Inspect visually and, where warranted, with a combustion analyzer. A cracked heat exchanger is a carbon-monoxide hazard and a red-tag.
- Inducer & pressure switch. Confirm the inducer spins freely and the pressure switch closes; blocked flues and cracked drain traps are the usual culprits on 90%+ furnaces.
- Condensate (high-efficiency). Clear the condensate trap and drain on condensing furnaces — a clogged trap trips the pressure switch and locks out heat.
- Gas pressure. Verify manifold pressure with a manometer against the nameplate (commonly ~3.5 iwc for natural gas), and check incoming supply pressure.
- Safeties. Confirm the rollout switch, high-limit, and flame rollout all function. Never jumper a safety to force a cycle.
- Temperature rise. Measure return and supply and confirm the rise falls within the nameplate range.
Temperature rise out of range = red flag
Gas furnace temperature rise (supply − return) must land inside the nameplate window, typically 35–75°F. Rise that's too high means low airflow and an overheating heat exchanger; rise that's too low can mean overfiring or oversized ductwork. Adjust blower speed to bring it into range — don't leave it out of spec.
Heat pumps run all year
On a heat pump, fall is when you verify defrost operation and the reversing valve, and confirm supplemental heat strips energize and lock out on schedule. In heating mode, charge and diagnostics rely on superheat at the outdoor coil — the indoor coil is now the condenser.
Worked Example: Verifying Cooling Capacity
Suppose you're on a 3-ton system in spring and want to confirm it's delivering rated sensible capacity. Use the airside sensible heat formula:
Sensible BTU/hr from airflow and temperature split
Step 1: Confirm airflow
A 3-ton system should move ~400 CFM/ton → 3 × 400 = 1,200 CFM.
Step 2: Measure the temperature split
Return air 75°F, supply air 57°F → ΔT = 75 − 57 = 18°F (within 14–22°F).
Step 3: Apply the formula
Qs = 1.08 × 1,200 × 18
Step 4: Solve
Qs = 23,328 BTU/hr sensible
Result: performing as expected
About 23,300 BTU/hr sensible on a 36,000 BTU/hr (3-ton) system is a healthy result — the balance is latent (moisture removal). If ΔT had come in at 10°F, sensible output would drop to roughly 13,000 BTU/hr, and you'd go hunting for low airflow or a charge problem before leaving the site.
Documentation That Prevents Callbacks
The difference between a tune-up and a professional PM is the paper trail. Record every reading — capacitor µF, static pressure, superheat/subcooling, delta-T or temperature rise, and gas pressure — with the target beside it. That record does three things:
- Proves the value of the visit to the customer with real numbers, not a checkbox.
- Builds a baseline so next season's tech can spot a capacitor or coil drifting out of range over time.
- Protects you if the system fails later — a documented in-spec reading shows the component was healthy on your visit.
Pro tip: photograph the nameplate
Snap the condenser and furnace nameplates on every PM. You'll have the rated capacitor value, refrigerant type and charge, and temperature-rise range on hand — and a photo tool can pull those specs for you so you're charging and setting rise to this unit's numbers, not a guess.
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