A thermostat set to 72 degrees should not leave a commercial space stuck at 78. That was the situation when a customer from Summerville, SC called our office for help with an AC system that would not cool properly. We arrived at 3:15 p.m. and began testing the controls, wiring, and equipment operation step by step.
The problem turned out to be more than a single failed part.
Two control boards were interfering with the system, and the zoned setup required careful troubleshooting to keep cooling available while we prepared the permanent repair.
Finding the First Failure in the Zoned System
We found proper voltage at the zone control board, but the board was not functioning correctly. This board coordinates thermostat calls and damper positions so each zone receives cooling when needed.
To get the system running, we bypassed the failed zone board. That temporary step revealed a second fault. The furnace control board was not sending voltage to the blower fan or the condenser, so the equipment still could not operate through its normal control sequence.
We then wired the fan and condenser directly to the thermostat. This temporary configuration restored interim cooling until both defective boards could be replaced.
The cooling temperature spread was limited during bypass operation.
All zones remained open, the bypass stayed open, and reduced air velocity affected performance. Still, the system was cooling instead of sitting idle, which mattered for a commercial property in Summerville during summer heat.
The National Weather Service maintains seasonal heat guidance for the South Carolina Lowcountry, where dependable cooling supports safe, usable indoor spaces.
Installing New Controls and Restoring Both Zones
We returned on July 15, 2026, checked in, and removed the defective zone control board. We mounted the replacement board directly to the furnace cabinet with self-tapping screws, then disconnected the thermostat wiring from the temporary bypass and completed the proper connections to the new board.
After restoring power, we found that the existing furnace board still would not send a signal to the blower relay. We replaced that board as well, completed the wiring, and powered the system again.
This time, the controls responded as designed.
Both zones cooled, both thermostats communicated properly, and the dampers operated with each zone. We also confirmed that the unit already had two transformers installed, an appropriate feature for this zoned configuration.
A Complete Commercial AC Repair in Summerville
The customer was extremely satisfied with the completed work. For us, the result came from staying methodical. Had we stopped after finding the first defective board, the repair would have remained incomplete. Testing after each step exposed the second failure and let us correct the full control problem.
At Arctic Air Inc., we provide commercial air conditioning service for businesses across Summerville and the Charleston area, including repairs, replacements, and preventive maintenance.
If your Summerville business has uneven temperatures, unresponsive zones, or an AC system that cannot reach its thermostat setting, schedule a diagnostic visit with our team. Prompt testing can help reduce downtime, uncover connected control problems, and restore dependable cooling before indoor temperatures climb further.
