Rooftop Package Unit Controller - SMT-850 Halo Freshdesk Guide
Support and commissioning guide for the Smart Temp SMT-850 Halo controller when used as the new rooftop package unit controller.
Safety and scope: Installer menu, wiring, relay outputs, BMS communications and rooftop package unit control settings must only be changed by a competent HVAC technician or electrician. Always follow the rooftop unit wiring diagram and installation instructions first. The Halo controller is low-voltage only and should not have mains voltage applied to low-voltage terminals.
Overview User operation Wi-Fi / App Installer setup Wiring / DIP RTU commissioning flow BMS / Comms Troubleshooting Ticket note
1. Controller overview
| Item | Support summary |
|---|---|
| Controller | Smart Temp SMT-850 Halo, 7 inch colour touch screen controller with Wi-Fi, scheduling, zone control and installer-configurable HVAC logic. |
| Application | Rooftop package unit control, including heat/cool or heat pump logic, fan control, staged outputs, 0-10 V outputs, optional zone dampers, economy functions and BMS interface where configured. |
| Support position | Confirm whether the fault is user operation, schedule/override, Wi-Fi/app, installer configuration, wiring/DIP switches, rooftop unit response or BMS communications before recommending controller replacement. |
| Installer PIN | Default installer PIN is 0021 unless changed by the installer. Do not change the PIN unless the site has agreed to a documented handover process. |
First question for support: Is the controller failing to operate the rooftop package unit, or is the customer asking how to use the screen/app/schedule? This determines whether to use the user flow or installer flow.
2. Basic user operation
| Function | Instruction | Support note |
|---|---|---|
| Mode | Press the Mode icon and select Off, Heat, Cool or Auto depending on the site requirement. | Auto mode allows the controller to decide heating or cooling based on set points and room temperature. |
| Set point | Use the up/down arrows beside Heat Set or Cool Set. | If an override ribbon appears, select the required override duration. In commercial mode, some stop/setback temperatures may be installer locked. |
| Fan | Select Fan Auto or Fan On where available. Fan speed may be shown if configured. | Available fan speeds depend on DIP and installer configuration. |
| Schedule | Press Schedule to edit times and occupied/unoccupied events where enabled. | Commercial mode typically uses Start and Stop events with an after-hours override timer. |
| Info / Alert | Press Info or the alert icon to see current status, errors and installer contact details. | Ask customer for a photo of the Info screen before dispatch where possible. |
3. Wi-Fi and app pairing flow
| Start: Customer wants app control or Wi-Fi connection |
| ↓ |
| Open More → Wi-Fi |
| ↓ |
| Tick Enable Wi-Fi, then select Setup Connection |
| ↓ |
| Scan for networks or use Hidden Network if SSID is not broadcast |
| ↓ |
| Select network, enter password and press Connect |
| ↓ |
| Decision - Does it show connection success and Pair App? |
| Yes | No |
|---|---|
| Open the Smart Temp app, select Add New Device / Scan and scan the QR code shown on the Halo controller. | Check password, Wi-Fi signal, router security setting, firewall/server access, and whether the network is hidden. If Wi-Fi joins locally but server confirmation fails, suspect firewall/router internet access. |
4. Installer setup flow
| Start: New rooftop package controller installation or replacement |
| ↓ |
| Step 1 - Isolate power to the rooftop unit and control circuit |
| ↓ |
| Step 2 - Photograph existing wiring and confirm rooftop package unit control requirements |
| ↓ |
| Step 3 - Mount Halo base level and land wiring to correct terminals |
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| Step 4 - Set DIP switches before powering up |
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| Step 5 - Enter Installer menu using PIN 0021 unless changed |
| ↓ |
| Step 6 - Configure equipment, fan, I/O, schedules, comms and zones/economy as required |
| ↓ |
| Step 7 - Exit and Save, then complete commissioning tests before handover |
5. Wiring and DIP switch reference
| Terminal / setting | Purpose | RTU support note |
|---|---|---|
| 24 / 24C | Controller power supply terminals. | Halo is typically 24 V AC but can run from low-voltage AC/DC within specification. Confirm polarity if DC powered. |
| R | Relay common for main outputs. | Factory link between 24 and R may be used or removed where volt-free outputs are required. |
| G / G1 | Fan or low fan speed. | If multi-speed fan is used, check SW1 and Aux relay allocation. |
| Y1 / Y2 | Cooling/compressor stages depending on heat/cool or heat pump logic. | Confirm stage count, anti-cycle timer, minimum run timer and rooftop unit staging logic. |
| W1 / O/B, W2 | Heat/reversing valve and auxiliary heat depending on DIP settings. | If heating runs in cooling or cooling runs in heating, check SW2/SW3 and reversing valve logic first. |
| Aux relays 1-5 | Assignable relay functions. | Can be used for additional compressor stages, alarms, economy dampers or other assigned functions. |
| UI 1-4 | Universal inputs for sensors, switches, alarms or 0-10 V inputs. | Use for outside air sensor, occupancy, fault or override inputs where configured. |
| AO 1-3 | 0-10 V analogue outputs. | Use for damper, valve, DC fan or inverter capacity control. The controller provides signal only; actuator motive power is external. |
| Comms A/B | RS-485 communications. | Used for Modbus RTU, BACnet MSTP and high-level/protocol adapter applications. |
| DIP | OFF | ON |
|---|---|---|
| SW1-1 Fan speeds | Single speed fan | Multi speed fan |
| SW1-2 Equipment logic | Heat / Cool | Heat Pump |
| SW1-3 Fan / reversing valve logic | Gas heat in HC mode or reversing valve on in cool when SW2 is ON | Electric heat in HC mode or reversing valve on in heat when SW2 is ON |
| SW1-4 | Leave OFF | Not used |
6. Rooftop package unit commissioning flow
| Start: Controller wired and installer options configured |
| ↓ |
| Step 1 - Test zones/dampers first if fitted Open all zones, physically confirm open. Close one at a time and physically confirm operation. Do not run rooftop unit with unsafe airflow. |
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| Step 2 - Test fan only Confirm G/fan output energises and rooftop unit fan responds correctly. Confirm speed control if configured. |
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| Step 3 - Test cooling call Set Cool mode and lower cool set point. Confirm correct Y/compressor stage, fan and any damper/economy output response. |
| ↓ |
| Step 4 - Test heating call Set Heat mode and raise heat set point. Confirm heat output, reversing valve logic and fan logic suit the rooftop unit. |
| ↓ |
| Step 5 - Test schedules and after-hours override Confirm occupied/unoccupied times, setback values and after-hours run timer if commercial mode is used. |
| ↓ |
| Step 6 - Test BMS or high-level interface if fitted Confirm address, baud, parity, stop bits, protocol and BMS point operation. |
| ↓ |
| End: Record settings, save/backup if required, and hand over basic user operation |
7. BMS / communications checks
| Check | Action |
|---|---|
| Protocol | Confirm communications mode: Modbus RTU, BACnet MSTP, Temperzone, Smart Temp UI, Intesis or other configured adapter. |
| Address | Confirm no two devices on the same node share the same network address. |
| Baud / parity / stop bits | Confirm all devices on the same RS-485 network share the same settings. |
| Wiring polarity | Check A/B polarity and shield grounding. Avoid star or branched wiring where RS-485 instability occurs. |
| Termination / bias | If communications are unstable after confirming settings and wiring, test SW2 communications DIP options for termination and bias according to site network requirements. |
8. Troubleshooting flow
| Symptom | First checks | Likely direction |
|---|---|---|
| Blank screen | Check 24/24C power, polarity if DC, control transformer and wiring at base. | Power supply or wiring issue before controller failure. |
| Rooftop unit does not start | Check mode, schedule, override, set point, installer lockout, anti-cycle/minimum run timers and output relay status. | If Halo output energises, fault may be rooftop unit wiring or rooftop control circuit. |
| Heating when cooling / cooling when heating | Check SW2 heat pump vs heat/cool, SW3 reversing valve logic, Y/W wiring and rooftop unit logic. | Configuration or crossed wiring issue. |
| Fan not operating | Check Fan Auto/On, SW1 fan speed selection, G/Aux relay allocation and fan control settings. | Fan configuration or rooftop fan control wiring. |
| Zone temperature inaccurate | Check correct Smart Temp sensor type, sensor wiring, sensor input assignment, RS-01/02 switch and location. | Sensor type, wiring or configuration issue. |
| Wi-Fi cannot connect | Check Enable Wi-Fi, password, signal strength, hidden network entry, security type and internet/server access. | Router/firewall issue if local Wi-Fi joins but server/app pairing fails. |
| BMS not seeing controller | Check protocol, address, baud, parity, stop bits, A/B polarity, shielding, topology and termination/bias. | Communications settings or RS-485 wiring issue. |
9. Freshdesk ticket note template
Suggested wording:
SMT-850 Halo rooftop package unit controller support completed. Site issue reported as: [insert]. Controller screen status checked: [OK / blank / alert shown]. Mode/schedule/set point checked: [insert]. Installer menu access required: [yes/no]. Default/known PIN: [insert only if appropriate]. Wiring checked: 24/24C power, R common, G/Y/W outputs, Aux relays, UI/AO and Comms A/B as applicable. DIP settings checked: SW1 fan speed, SW2 heat/cool vs heat pump, SW3 fan/reversing valve logic, SW4 left off. RTU output test completed: fan [OK/not OK], cooling [OK/not OK], heating [OK/not OK], zones/economy [OK/not applicable], BMS [OK/not applicable]. Result/recommendation: [insert].
SMT-850 Halo rooftop package unit controller support completed. Site issue reported as: [insert]. Controller screen status checked: [OK / blank / alert shown]. Mode/schedule/set point checked: [insert]. Installer menu access required: [yes/no]. Default/known PIN: [insert only if appropriate]. Wiring checked: 24/24C power, R common, G/Y/W outputs, Aux relays, UI/AO and Comms A/B as applicable. DIP settings checked: SW1 fan speed, SW2 heat/cool vs heat pump, SW3 fan/reversing valve logic, SW4 left off. RTU output test completed: fan [OK/not OK], cooling [OK/not OK], heating [OK/not OK], zones/economy [OK/not applicable], BMS [OK/not applicable]. Result/recommendation: [insert].
Escalation trigger: Escalate before replacing the controller if outputs are energising correctly but the rooftop unit does not respond, if BMS settings are unknown, if the installer PIN has been changed and not documented, or if mains voltage may have been applied to a low-voltage terminal.