Commercial Rooftop Units · Central Oklahoma

Commercial rooftop unit repair in Central Oklahoma

4.8 stars, 300+ Google reviews

A rooftop unit is a complete air conditioning system built into one cabinet that sits
on the roof, and when it stops, the whole building stops with it. I am Dave Hartzell.
I have worked in HVAC/R since 1980, and I repair commercial rooftop package units across seven
Oklahoma counties: Kingfisher, Canadian, Oklahoma, Garfield, Major, Logan and Blaine.

What is a rooftop unit and how is it different from a split system?

A rooftop unit, often called an RTU or a package unit, holds the compressor, condenser, evaporator coil and blower in a single cabinet on the roof, while a split system divides those parts between an outdoor condenser and an indoor furnace or air handler. Everything on a package unit is in one place, which makes it faster to diagnose and means nobody has to walk through your building to service it. It also means one failure on the roof takes the whole zone down, because there is no second half of the system to keep running.

How much does commercial rooftop unit repair cost in Oklahoma?

A commercial HVAC diagnostic from Hartzell’s Heat & Air is $389 flat for light commercial equipment up to 15 tons, and it is the same price day or night. That covers the trip and the diagnosis, and it is bookable online. There is no after hours surcharge and no weekend uplift. Units larger than 15 tons are sized and quoted by the technician on site. Repair cost on top of the diagnostic depends on the part, and I tell you the number before I do the work.

What are the most common commercial rooftop unit failures?

The failures I find most often on commercial rooftop units are burnt contactors, failed run capacitors, seized condenser fan motors, dirty condenser coils, worn blower belts, control transformer failures and economizer linkage problems. Most of them are control side or airflow side rather than the compressor itself. That matters to a building owner, because a compressor is the expensive part and it is usually not the part that failed. It is the part that gets blamed.

Why will a brand new rooftop unit not run?

A brand new rooftop unit that will not run is almost always a control problem rather than a failed compressor, and the diagnosis starts by proving whether incoming power is good and then working through the control circuit. On a September 2026 commercial call in Guthrie, the equipment on the roof was new, had been installed by a different company, and would not run. The chain was a burnt control transformer, a phase monitoring fault, and a failed machine control board. Voltage balance measured good, which pointed away from incoming power and toward the control side, and the equipment manual confirmed the transformer lands on the same connection as the phase monitor.

What is a phase monitor and why does it shut a rooftop unit down?

A phase monitor is a protective device on three phase equipment that watches the incoming power for a lost leg, reversed rotation or voltage imbalance, and it shuts the unit down before those conditions can destroy the compressor. Because it is a protection device, a phase monitor fault reads like a power problem when it is often a wiring or control fault instead. The test is to measure voltage balance across all three legs. If the power is balanced and the monitor is still faulting, the problem is on the control side, and chasing the utility is wasted time.

Can a rooftop unit be run temporarily while parts are on order?

Yes, a commercial rooftop unit can sometimes be run temporarily using documented workarounds when factory parts are not immediately available, and any contractor doing it should tell you plainly that the measure is temporary. On the Guthrie call, factory parts were roughly a week out. Two variable speed condenser fan motors could not be driven with the control board dead, so they were replaced with standard motors tied into the compressor contactors, and the indoor blower drive was bypassed. That kept the building cooling through the weekend. It was described as temporary at the time, not as a completed repair, and the proper parts still had to go in.

Do you work on rooftop units installed by another contractor?

Hartzell’s Heat & Air regularly services commercial rooftop equipment installed by other companies, including new equipment still inside its manufacturer warranty. A second opinion on new equipment is one of the more common commercial calls I take. The equipment being new does not mean it is right, and it does not mean you have to wait on the original installer while the building is hot.

For commercial pricing, response times, and what I service across central Oklahoma, see my commercial HVAC page. Restaurants are one of the most common buildings I do this work in, so if you run one, see my restaurant HVAC page for makeup air, grease and refrigeration questions. The Guthrie call I walk through above is written up in full in my Guthrie commercial AC case study.