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Undermount AC Wi‑Fi Controller User Manual

Guide for using the controller web interface. Covers normal operation, cooling, fan control, Heat Box, Basic Heat, firmware updates, watchdog recovery, API, and MQTT controls.

CoolingFan speedsHeat BoxBasic HeatFirmware updateWatchdog

1. Connecting to the controller

Power the controller from the normal vehicle or bench supply.

Open Wi‑Fi settings on the phone, tablet, or 5 inch Android display.

Connect to the network beginning with UNDERMOUNTAC-.

Use password 12341234 unless the password has been changed.

Open a browser and go to http://10.10.10.10.

The controller can also join another Wi‑Fi network from the Wi‑Fi & MQTT Settings page. The built-in controller access point remains the normal local access method.

2. Main screen controls

Control	What it does
Mode buttons	Off, Fan, Cool, and Heat. Heat is shown only when Heat Function Enabled is turned on in Settings.
Set temperature	Raises or lowers the target temperature. °F uses whole degrees. °C uses clean 0.5°C steps such as 22.0, 22.5, 23.0.
Fan Mode button	Cycles fan behavior. See the Fan section for Auto, Fixed, and Continuous behavior.
Fan level slider	Sets the selected blower level from 1 to 7 when manual fan control is active.
Compressor speed card	Shown in Off/Fan/Cool. Selects Low, Auto, or High compressor behavior.
Heating card	Shown in Heat mode. It replaces the compressor speed card so the page size and layout remain the same.
Status / Settings button	Opens live diagnostics, configuration, firmware update, and manual access.

3. Cooling operation

When cooling starts and stops

Cooling starts when the cabin temperature is about 1°F above the set temperature.
Cooling stops when the cabin reaches the set temperature, after the minimum compressor run time has been met.
If the controller says Waiting to start, it is protecting the compressor before allowing another start.

Compressor protection delays

Status text	Meaning
Compressor start delay	The compressor has started, but the blower/high stage is delayed briefly to let pressures stabilize. This is normally about 20 seconds.
Waiting to start	The compressor recently stopped and is waiting before restart. This is normally about 2 minutes after a normal cooling shutdown.
Cooling low	Cooling is active in low compressor speed.
Cooling high	Cooling is active in high compressor speed.
Blower post-run	The blower continues briefly after cooling stops to clear remaining cold air from the evaporator.

Compressor speed modes

Mode	Behavior
Low	Uses low compressor speed whenever cooling is active.
Auto	Automatically uses high speed when the cabin is far above setpoint or after a long cooling run.
High	Requests high speed cooling when the system is able to run it.

High compressor speed is only allowed when blower airflow is high enough. If the selected fan level is too low, the controller protects the system by keeping the compressor in low speed.

5. Fan modes and speeds

Fan modes

Fan mode	Behavior
Auto	The controller stages blower speed automatically during cooling based on how far the cabin is from the set temperature.
Fixed	Uses the selected blower level while cooling is active.
Continuous	In Cooling mode, the blower keeps running between compressor cycles at the selected level.
Fan Only mode	Runs the blower without heating or cooling. If fan selection is Auto, Fan Only uses a mid-level blower setting.

Fan levels

The blower has seven protected speed levels. Level 1 is the lowest running level and Level 7 is the highest.

Level	Approximate request
1	Low airflow
2–4	Medium airflow
5–7	High airflow

The displayed percentage is a protected blower request, not a direct electrical duty cycle. The controller maps each level to calibrated blower output.

Blower delays

Cooling start delay: the blower may wait briefly after the compressor starts.
Cooling post-run: after cooling stops, the blower may continue for about 20 seconds.
Heat post-run: after a cabin heat call is satisfied, the blower may continue for about 60 seconds.

5. Heating operation

Heating is available only when Heat Function Enabled is turned on from Status / Settings.

Heat Box

Heat Box is for the external relay box. It supports cabin heat, water heating, and aux heat behavior.

Feature	Behavior
Cabin heat	In Heat mode, the heat valve opens and stays open. When the cabin is below set temperature, the heat call stays ON until satisfied.
Water Heater	Uses the hydronic heater loop to heat water through a heat exchanger. In the current UI it is shown on the Heat card.
Aux Heat	Located in Settings. When enabled, it turns on aux heat behavior and blocks the shared hydronic heat output.

Basic Heat

Basic Heat is for a simpler two-relay installation. It does not use the external RS485 relay box.

Feature	Behavior
Heat valve	Opens while the system is in Heat mode.
Heater call	Turns on when the cabin is below the set temperature and stays on until satisfied.
Water/Aux	Water Heater and Aux Heat are hidden/disabled in Basic Heat.

Heat call behavior

There is no heat start delay.
Heat outputs are latched for the full heat call. They are not momentary pulses.
The heat valve stays open for the full time the controller is in Heat mode.
When the cabin reaches set temperature, the heat call turns off and the blower may run a short post-run.
Leaving Heat mode turns off Heat-mode-only outputs. In the current version, Water Heater is also turned off when leaving Heat mode.

6. Status / Settings page

This page is used for configuration and live status. Normal users may only need it for temperature units, heat setup, firmware updates, and the manual.

Item	Purpose
Firmware	Shows the installed controller firmware version and boot count.
Uptime	Shows how long the controller has been running since the last restart.
Sensor	Shows live sensor status, temperature/humidity, and whether the sensor is responding.
Control phase	Shows what the controller is currently doing, such as Ready, Cooling Low, Cooling High, Waiting to Start, Heating, or Blower Post-run.
Wi‑Fi AP	Shows the controller access point name, IP address, connected clients, and station/MQTT state if configured.
Temperature units	Switches between °F and °C.
Heat Function Enabled	Shows or hides Heat mode and heat settings.
Heat Type	Selects Heat Box or Basic Heat.
Aux Heat	Heat Box only. Enables aux heat behavior and blocks the shared hydronic heat call.
Outputs	Shows the current output states for blower, compressor, heat valve, heater, water heat, and aux heat.
Event log	Shows recent restarts, recoveries, watchdog status, network recovery, and memory warnings.

7. Firmware update page

The controller includes a built-in firmware update page for customer updates.

Connect to the controller web page.

Open Status / Settings.

Press Firmware Update.

Select the update file provided for your controller.

Press Upload and install firmware.

Keep power connected until the controller finishes and restarts.

Do not turn power off during a firmware update. If the page does not return immediately after the restart, wait about a minute and reconnect to the controller Wi‑Fi.

8. Wi‑Fi and MQTT settings

The controller can run from its built-in access point and can also join another Wi‑Fi network. MQTT is optional and is intended for advanced integration systems such as Home Assistant.

Feature	What it does
Controller access point	Lets you connect directly to the controller even when there is no router or internet.
Station Wi‑Fi	Allows the controller to join another Wi‑Fi network.
MQTT	Allows status and control through an MQTT system when configured.
Home Assistant discovery	When MQTT is configured, the controller can advertise controls and sensors automatically.

9. Watchdog, recovery, and event log

The controller includes a built-in health monitor. This is intended to keep the web interface and control loop reliable during long use.

Watchdog

The watchdog checks that the controller firmware is still running normally. If the controller ever becomes stuck, the watchdog can force a restart.

A Status / Settings value of Watchdog: Armed is normal and good.

Network recovery

The controller checks that its web access path is still available. If the network path is lost, it tries to recover the web server and access point. If repeated recovery attempts fail, the controller may restart to restore access.

Event log

The event log stores recent controller events, newest first. It can help explain why the controller restarted, recovered Wi‑Fi, or detected a fault.

Event type	Meaning
WATCHDOG	The watchdog was started or reported a problem.
NETWORK RECOVERY	The controller had to recover the web/network path.
RESTART	The controller restarted itself for recovery or after firmware update.
MEMORY	The controller detected low memory or memory recovered.

If the system is operating normally, occasional boot or setup events are not a problem. Repeating fault or recovery events should be reported with a photo or screenshot of the Status / Settings page.

10. Troubleshooting

Symptom	What to check
Cannot connect to controller	Confirm the controller has power, reconnect to the UNDERMOUNTAC- Wi‑Fi network, then browse to 10.10.10.10.
Controller says Ready but not cooling	Check that Mode is Cool, the set temperature is below cabin temperature, and there is no compressor restart delay.
Controller says Waiting to start	The compressor recently stopped. Wait for the restart protection timer to finish.
Blower does not start immediately with cooling	This may be the normal compressor start delay. The blower should start after the delay if cooling remains active.
Heat option missing	Open Status / Settings and turn on Heat Function Enabled.
Water Heater missing	Water Heater is available only with Heat Box and is currently shown in Heat mode.
Aux Heat missing	Aux Heat is shown only when Heat Type is Heat Box.
Temperature steps look wrong	Switching °F/°C snaps the set temperature to the correct grid. °C should move in 0.5°C steps.
Sensor fault	The temperature/humidity sensor is not responding. Heating and cooling outputs are disabled until the sensor recovers.

11. Advanced API and MQTT reference

These features are optional. They are provided for customers using a remote display, automation system, Home Assistant, or another connected controller. Normal operation from the web page does not require using API or MQTT commands.

HTTP API overview

Endpoint	Purpose	Notes
`/api/status`	Returns live controller status as JSON.	Use this for dashboards, remote displays, and diagnostics.
`/api/set`	Changes controller settings using query parameters.	Examples: `/api/set?mode=cool`, `/api/set?setpoint=72`.
`/firmware`	Opens the firmware update page.	Upload only firmware files supplied for this controller.
`/manual`	Opens this built-in manual.	Available directly from the controller.

API status fields

Field	Meaning
`version`	Installed firmware version.
`mode`	Current operating mode: `off`, `fan`, `cool`, or `heat`.
`phaseText` / `phase`	Human-readable current activity, such as Ready, Cooling, Waiting to Start, Heating, or Fan Post-run.
`temp` / `temperature`	Live cabin temperature.
`humidity`	Live humidity reading.
`setpoint`	Current set temperature.
`temperatureUnit` / `temperature_unit`	Current display unit: `F` or `C`.
`fanMode` / `fan_mode`	Fan behavior: Auto, Continuous, Fixed, or Cycle depending on firmware options.
`fanLevel` / `fan_level`	Selected fan level from 1 to 7.
`fanPercent` / `fan_percent`	Actual blower output percentage.
`compressorMode` / `compressor_mode`	Compressor speed selection: Low, Auto, or High.
`compressor`	Whether compressor output is currently active.
`blower`	Whether blower output is currently active.
`heatFunctionEnabled` / `heat_function_enabled`	Whether Heat mode and heat features are enabled.
`heatType` / `heat_type`	Selected heat hardware: `box` for Heat Box or `basic` for Basic Heat.
`heating`	Whether cabin heat demand is currently active.
`heatValveOpen` / `heat_valve_open`	Whether the heat valve output is active.
`waterHeating` / `water_heating`	Whether Water Heater is currently active. Heat Box only.
`auxHeating` / `aux_heating`	Whether Aux Heat is enabled. Heat Box only.
`heatSharedRelay` / `heat_shared_relay`	Whether the shared hydronic heat demand output is active.
`fault`	Fault text, if a fault is active.

API set commands

Command	Allowed values	What it does
`/api/set?mode=...`	`off`, `fan`, `cool`, `heat`	Changes operating mode. Heat is accepted only when Heat Function Enabled is on.
`/api/set?setpoint=...`	Valid temperature value	Changes the set temperature. °F uses whole-degree steps. °C uses 0.5°C steps.
`/api/set?unit=...`	`F`, `C`	Changes the displayed temperature unit.
`/api/set?fanMode=...`	`auto`, `continuous`, `fixed`, `cycle`	Changes fan behavior where supported by the firmware.
`/api/set?fanLevel=...`	`1` through `7`	Changes selected fan level.
`/api/set?compressor=...`	`low`, `auto`, `high`	Changes compressor speed behavior in Cool mode.
`/api/set?heatEnabled=...`	`1`, `0`, `on`, `off`	Shows or hides Heat mode and heat settings.
`/api/set?heatType=...`	`box`, `basic`	Selects Heat Box or Basic Heat.
`/api/set?waterHeating=...`	`on`, `off`, `toggle`	Controls Water Heater. Heat Box only; not used in Basic Heat.
`/api/set?auxHeating=...`	`on`, `off`, `toggle`	Controls Aux Heat. Heat Box only; not used in Basic Heat.

MQTT overview

MQTT is optional. When enabled, the controller publishes a retained status message and accepts command topics. The base topic defaults to undermountac/<controller-id>. The exact base topic is shown on the Wi‑Fi & MQTT settings page.

Topic	Purpose
`<base>/state`	Retained JSON status payload containing live controller state.
`<base>/availability`	Reports `online` or `offline`.
`<base>/set/#`	Command topic area. Publish values to the specific command topics below.

MQTT command topics

Topic	Allowed payloads	What it controls
`<base>/set/mode`	`off`, `fan`, `fan_only`, `cool`, `heat`	Operating mode.
`<base>/set/setpoint`	Number in the currently selected temperature unit	Set temperature.
`<base>/set/temperature_unit`	`F`, `C`	Temperature display unit.
`<base>/set/fan_mode`	`auto`, `continuous`, `fixed`, `cycle`	Fan behavior.
`<base>/set/fan_level`	`1` through `7`	Manual/fixed fan level.
`<base>/set/continuous_fan`	`on`, `off`, `1`, `0`, `true`, `false`	Continuous fan toggle.
`<base>/set/compressor_mode`	`low`, `auto`, `high`	Compressor speed selection.
`<base>/set/heat_enabled`	`on`, `off`, `1`, `0`, `true`, `false`	Enables or disables Heat Function.
`<base>/set/heat_type`	`box`, `basic`	Selects Heat Box or Basic Heat.
`<base>/set/water_heater`	`on`, `off`, `toggle`	Water Heater control. Heat Box only.
`<base>/set/aux_heat`	`on`, `off`, `toggle`	Aux Heat control. Heat Box only.

MQTT state JSON fields

The <base>/state payload includes the current mode, setpoint, live sensor readings, fan state, compressor state, heat state, output state, phase text, fault text, and firmware version. Important fields include:

versionmodesetpointtemperaturetemperature_unithumiditysensor_okfan_modefan_levelfan_percentcompressor_modecompressorblowerphaseheat_function_enabledheat_typeheatingheat_valve_openwater_heatingaux_heatingheat_shared_relayfault

Home Assistant discovery can expose climate, fan, compressor, humidity, phase, heat enable, heat type, Water Heater, and Aux Heat entities when MQTT and discovery are enabled.