A new 10-ton unit running on a 1980s building automation system
A 38-year-old rooftop unit failed on a multi-tenant office building in Commerce Township. Two days on the roof later, a new Trane unit was running the building's zones through its original Trane Tracer system, and every tenant kept zone control.
- 38 yearsAge of the unit that was replaced
- 2 daysOn the roof, about 34 team hours, plus start-up
- 10 unitsNow on a three-visit maintenance agreement
The challenge
The middle rooftop unit on this multi-tenant office building had been working since the 1980s. In June 2026 it lost its first-stage compressor. The building's zones are run by an original Trane Tracer building automation system: the rooftop units feed VAV boxes in each suite, and the Tracer system decides how much air each zone gets.
Our team tried to save the old unit first. Steve Locher and Doug Hebert installed a new compressor, pressure-tested the system with nitrogen and repaired four leaks in the lines and the coil. Then a fifth leak showed up in the coil. A coil with that many leaks is finished, and more repairs would have been money spent on a unit that could not last. They stopped and told the owner's representative, who decided to replace the unit.
The hard part was the controls. Nobody could promise that a brand-new controller would talk to a building automation system from the 1980s, so the quote for the new unit said in writing that the VAV box controls and the building automation system were not included. The fallback, if the new unit would not work with the old system, was to open every VAV box by hand, run thermostat wire down, and hang one thermostat in one office for the whole building.
What we did
1. Stop repairing when the evidence says stop
The compressor that had just been installed came back out when the old unit reached the shop. Telling the owner to stop spending on the old unit was the right call, even with a new part already in it.
2. Quote the whole job and state the risk
The quote covered a 10-ton Trane unit with a Symbio 700 controller, 10:1 modulating gas heat, a low-leak economizer, a VAV supply fan motor and BACnet communication, plus custom insulated duct, a steel I-beam to carry the heavier unit, a disconnect bracket and start-up. It was approved in July.
3. Set the unit in two days
On August 4 Steve Locher, Hazen Draves and Joe Burton disconnected the old unit, craned it off, set the new beam and the new unit, and made the duct connections. Steve had built the transition duct in the shop beforehand. When the old feeder wires turned out to be burned, the team removed them and installed a new fused disconnect, a junction box and spliced feeders. Hazen and Steve finished the install on August 7.
4. Make the new unit talk to the old system
The team kept the Tracer boards from the old unit instead of scrapping them with it. On August 10 Robert Black took those boards back up to the roof, checked and corrected the electrical phase, and wired the new unit to operate with the building's Tracer system. He set up the economizer, checked the amp draw on every motor and compressor, and cycled the unit. The building kept its zone control.
5. Finish the roof while we were there
Robert found the older cooling-only unit next to it low on charge and brought it back with 20 lb of R-22. Later in August, when suites 120 and 130 had no cooling, Kory Pass traced it to two failed 24-volt zone actuators and replaced them. The rooftop units were fine; the zones were not getting the signal.
6. Turn a breakdown into a plan
With the roof fresh in the owner's mind, we offered a three-visit maintenance agreement for the building's 10 rooftop units and exhaust fan: a fall heating check, a spring cooling check and a summer coil wash. The owner signed. The first visit ran in late September: Ian Smith and Kory Pass spent 17.5 hours on the roof, replaced 32 filters and 2 belts, and wrote an inspection report for every unit.
Results
- Zone control kept. Tenants kept suite-by-suite control from the system they already had, instead of one thermostat for the building.
- A current unit on an old building. A 10-ton Trane with a Symbio 700 controller, BACnet and a 15-year heat exchanger warranty.
- A fully inspected roof. Every unit has a report, and the building is on a maintenance agreement three times a year.
Worth knowing
When a new unit lands under an old building automation system, decide before install day how it will be controlled, keep the old controller boards until start-up is proven, and write the fallback plan on the ticket. The mechanical service trade's own standards put controls skills, documented safety programs and first-time fixes at the center of what separates good contractors; this job needed one more trip than planned, and the ticket says why.
Sources: MSCA STAR contractor qualification, as described by FacilitiesNet; ServiceTitan field service metrics guide (first-time fix, repeat visits). From the AHS service records for this job.