Commercial RTU Controls Repair at Panera Bread in Melbourne, FL

2R Cooling & Refrigeration responded to a commercial HVAC control concern at a Panera Bread location in Melbourne, Florida. Four Honeywell commercial thermostats controlled separate rooftop systems. The primary concern involved thermostat and RTU #3, where the occupied area felt considerably warmer than the temperature being used for control.

• The rooftop controller showed the building occupied and the blower operating at approximately 83%.
• The G fan input was active, but Y1 and Y2 cooling inputs were inactive.
• Return-air temperature was approximately 76°F and discharge-air temperature approximately 80°F, confirming the blower was operating without an active mechanical cooling demand.
• A stored blower fault was investigated, but the blower motor was physically operating and continued running during inspection.
• A humidity-sensor notification was also present, but it was not identified as the cause of the missing cooling demand.

The remote sensors were installed and wired, but the installer configuration was incorrect: the sensor input was configured for 20K instead of the installed 10K sensor, the wired remote indoor sensor was not selected correctly, the thermostat's internal sensor was selected for temperature control, and the remote-zone sensor was not being used as the controlling temperature. Because all four thermostats were mounted together away from their respective served areas, the systems were controlling from the temperature at the thermostat bank instead of the actual remote zones.

• Inspected all four thermostat and remote-sensor circuits.
• Verified the two-wire S1/S1 sensor wiring.
• Tested remote-sensor resistance.
• Confirmed sensor response to temperature changes.
• Corrected the sensor type from 20K to 10K.
• Selected S1 as the wired indoor-sensor input.
• Enabled each remote indoor sensor.
• Disabled the thermostat's internal sensor for temperature control.
• Configured each thermostat to control from its respective remote zone.
• Verified the primary cooling demand after the normal compressor protection delay.

After correcting thermostat #3, its displayed indoor temperature changed from approximately 77°F to 81°F and then stabilized near 82°F. The measured temperature near the remote sensor was approximately 83.1°F. The thermostat initially displayed “System Wait” during the normal compressor anti-short-cycle delay and then changed to “System Cool On,” confirming that the thermostat recognized the warmer remote-zone temperature and restored the cooling demand. The other three thermostat configurations were also inspected and corrected to use their corresponding 10K remote sensors. No equipment was replaced — the correction was completed through testing, configuration and verification.

The thermostats were equipped with two-wire remote indoor temperature sensors connected to S1 and S1. These are non-polarized resistive sensors, so conductor color and polarity do not affect operation.

The remote sensor and field circuit were isolated and tested by resistance. Measurements included approximately 8.55 kΩ directly at the sensor and approximately 9.05–9.30 kΩ through the field wiring as the sensor stabilized. Temperature near the remote sensing location was approximately 82.9–83.1°F. The resistance changed normally with temperature, demonstrating that the remote sensor itself was responding properly.

Thermostat displays #3 and #4 were temporarily exchanged as an A/B diagnostic test. The incorrect displayed temperature followed the thermostat display rather than the remote sensor circuit. This established that the issue was related to thermostat configuration — not a failed remote sensor or rooftop blower motor.

The thermostat setup showed the Indoor Sensor Type configured for a 20K sensor while the installed remote sensor was a 10K NTC type. Because the thermostat interpreted the sensor's resistance against the wrong curve, that mismatch contributed to the inaccurate displayed temperature.

All four thermostats were then audited for the same configuration condition.

Systems evaluated

Four commercial rooftop HVAC systems

Primary concern

RTU/thermostat #3

Sensor configuration

Two-wire S1/S1

Sensor type

10K NTC

Direct resistance measurement

Approximately 8.55 kΩ

Field-circuit measurement

Approximately 9.05–9.30 kΩ

Remote-area temperature

Approximately 82.9–83.1°F

Initial RTU condition

Blower operating; no Y1/Y2 demand

Final thermostat #3 condition

Approximately 82°F; System Cool On

Corrective action

Remote sensor configuration corrected on all four thermostats