What is wrong? › Commercial HVAC
Something else: the general first aid for a commercial system
Most commercial HVAC calls come down to power, filters, drains or controls. Rule those out before paying for a diagnosis, then use the seven universal questions on the call.
What is probably happening
- Noise, a smell when the fan starts, one room off, a unit that runs all the time, a thermostat that does what it wants.
- If it is a smell of gas or a CO alarm, stop and use the gas or CO leaf now.
- If it is a walk-in or reach-in cooler, that is a refrigeration contractor. If it is a kitchen hood, that is a hood contractor.
Do this in the next five minutes
- Check the thermostat: mode, setpoint, schedule, batteries.
- Check the unit's breaker. Reset once. If it trips again, leave it off.
- Change reachable filters and note the date.
- If you rent, read the HVAC clause in the lease before calling anyone.
- Write down what you see, hear and smell, and when it started. Then call a licensed commercial HVAC contractor with the seven universal questions ready.
Do not
- Do not go on the roof. OSHA's fall protection duty starts at 4 feet above a lower level.
- Do not open the unit's panels. There are high voltage terminals and, on gas units, a burner section.
- Do not accept a replacement quote before a written diagnosis.
Who to call
A licensed commercial HVAC contractor
Rooftop units and commercial split systems combine gas, electrical and refrigerant in one cabinet. Check the state license (in Texas, for example, the TDLR requires a license to install, repair or maintain air conditioning, refrigeration or heating) and EPA Section 608 certification.
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What it should cost
$100 to $250 service call; repairs $100 to $3,000, averaging $350
HVAC diagnostic visit and repair, national range
Source: Angi, HVAC repair cost, updated August 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the commercial hvac page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- Are you licensed for commercial HVAC work in this state, and what is the license number?
- What is your EPA Section 608 certification type?
- What is the diagnostic fee, and is it credited against the repair?
- Will you put the finding and the price in writing before any work?
- Can you send a certificate of insurance naming my business as certificate holder?
End the call if
- A replacement quote on the first visit with no readings.
- Full payment up front or cash only.
- No license number offered.