The two rooftop HVAC visits a year that pay for themselves

Rooftop units fail in July and January, never in the shoulder months, and never on a Tuesday morning. That is not bad luck. It is the fact that nothing on a roof gets looked at until it is asked to run at 100 percent capacity, and by then a $35 part has already taken out a $2,400 compressor.

The reason to care is that a rooftop unit failing in August is not a repair, it is a closed day. A restaurant cannot seat a 90 degree dining room, and the kitchen behind it gets hotter than the dining room does. A salon with no cooling loses a full Saturday book, because nobody sits through a color service in that room and the staff cannot work in it either. You do not get those hours back the following week.

Two visits a year fixes most of it. Here is what each one has to include and why.

The spring visit, booked for April

Book it before the first 90 degree day, because after that every HVAC company in your market is on emergency calls and a scheduled maintenance visit slides to August.

• Condenser coil cleaning. This is the single highest-value task on the roof. A dirt film on the coil raises head pressure, cuts capacity and adds meaningfully to compressor draw. Where a kitchen exhaust fan discharges anywhere near the unit, the coil loads up in a single season, which is why restaurants get this bill and offices do not.
• Capacitor testing under load. A run capacitor that measures below about 90 percent of its rated microfarads is a replacement, and the part is $20 to $60. A weak capacitor is the most common reason a compressor draws locked-rotor current on a hot afternoon and never starts again.
• Contactor inspection. Pitted or welded contacts run hot and eventually stick closed. A contactor is $40 to $90.
• Refrigerant charge verified by superheat and subcooling, not by gauge pressure alone. A unit that is 15 percent low on charge still cools, badly, and quietly runs the compressor hotter than it should for the rest of the summer.
• Belt tension and blower wheel. A blower wheel caked with dust moves less air across the coil, which looks exactly like a refrigerant problem from the dining room.
• Condensate pan and drain. Clear the trap, treat the pan, confirm the float switch actually cuts the unit. A blocked drain on a rooftop is how a ceiling tile lands on a table at seven o'clock.
• Economizer dampers. An economizer is a linkage, an actuator and a damper blade sitting outdoors in the weather, and when it seizes it seizes in one of two positions: shut, which throws away free cooling in the spring, or open, which lets 95 degree air into the room at noon. Neither failure trips anything or shows on a thermostat, so it goes unnoticed until somebody strokes the damper through its full range. Ask for that on the ticket. Actuators run $180 to $400 and pay back quickly.

The fall visit, booked for October

• Heat exchanger inspection, visual and with a combustion analyzer. Cracks put combustion gases into the supply air. This is the item on the list with a safety consequence, and it is the reason the fall visit is not optional.
• Flame sensor, igniter and burner cleaning. A dirty flame sensor is the classic no-heat call on the first cold morning, and it is a ten minute cleaning.
• Gas pressure and combustion readings recorded on the ticket so next year's numbers mean something.
• Carbon monoxide check in the return and in the store.
• Filters and outdoor air settings for the heating season, with the economizer set back.
• Roof penetrations and curb gaskets. Every technician on a roof should be looking at the flashing around the curb. Water in a store from a rooftop unit almost never comes through the unit itself.

Filters are your job, not theirs

Between visits, change filters on your own schedule. A restaurant or a cafe should be on MERV 8 every 60 days, and every 30 if a fryer or a griddle sits anywhere near a return. A salon breathing hair, powder and aerosol is on the same 30 day interval for the same reason. Write the date on the filter frame in marker. Restricted airflow is the cause of a large share of frozen coils and high-limit trips, and it costs you nothing but attention.

A dining room that drifts to 78 F on a Saturday night shortens how long people stay at the table, and a salon at that temperature becomes a review about the room rather than the haircut. Interior comfort is a sales variable, not just a comfort one.

The numbers that make the case

Two maintenance visits on one 5 ton rooftop unit run $340 to $700 a year, more with multiple units. Against that:

• Compressor replacement: $2,400 to $4,800
• Blower motor: $600 to $1,200
• Gas valve or control board: $450 to $900
• Full 5 ton unit replacement with crane and curb adapter: $9,000 to $14,000
• Emergency after-hours diagnostic in July: $250 to $500 before any part

Maintained units run three to five years longer than neglected ones, and the failures they do have happen during business hours because someone caught the weak part before it took out the expensive one. That is the whole return on the program.

What to keep on file

Photograph every data plate and keep a one-page asset sheet per unit: make, model, serial, tonnage, refrigerant type, filter sizes and quantity, capacitor ratings, install year. When something fails at 5 PM, that sheet is the difference between a pro arriving with the part and a pro arriving to take a look.

Also keep the last two service tickets with the recorded superheat, subcooling and amp draws. Trend beats snapshot: an amp draw that has crept up 12 percent over two years tells you more than any single reading.