Room Fan Motor Testing for TQ/TQM Heaters
Overview
Most TQ/TQM heater models include a Forward-Curved Centrifugal (FCC) room fan, typically sized 9x7 or 10x10. The fan is powered and controlled by the ICS (Integrated Control System), with speed modulation managed via a triac circuit.
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Fan Speed Configuration
Single-Stage Heaters
• Maximum System Fan Speed Adjustment Method: Trim-pot on ICS (next to thermostat connector)
• Speed Range: 7 (min) to 10 (max)
• Fully anticlockwise = Speed 7
• Fully clockwise = Speed 10
Two-Stage & Modulating Heaters
• Maximum System Fan Speed Adjustment Method: MagIQtouch Controller setup routine - 7378 to access
• Speed Range: 7 to 10 (via on-screen prompts)
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Fan Speed Operation
Single-Stage Heaters
• Starts at speed 1 ~10 seconds after ignition
• Increases 1 step every 5 seconds until max speed
Two-Stage & Modulating Heaters
• Starts at speed 1 ~10 seconds after ignition
• Increases 1 step per °C from 40°C to 50°C
• Max speed reached at 50°C
• Speed decreases only when:
• Heat cycle ends
• Thermistor temp drops to 40°C
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Incorrect Fan Speed Settings – Effects
Incorrect fan speed settings can lead to:
Poor heater performance
Increased running costs
Fan speed is determined by:
Maximum system fan speed set at installation (Speed 7–10)
Programmed zone fan speed settings
User-set fan speed (not applicable to single-stage heaters)
Thermistor temperature (not applicable to single-stage heaters)
Gas Rate Limiting (Modulating Heaters Only)
If the user adjusts the fan speed the gas rate will modulate down as per below
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Troubleshooting
Fan Does Not Start
Power Off Checks:
• Ensure wiring is secure and correct at ICS (brown, blue, black wires)
• Verify capacitor connections (blue wires)
• Refer to wiring diagram under heater lid
Motor Resistance Check (fan must be stationary):
Capacitor Testing:
• Disconnect power and discharge the capacitor safely.
• Use a multimeter with capacitance mode or a dedicated capacitor tester.
• Compare measured capacitance to the rated value (typically printed on the capacitor).
• A reading significantly lower than the rated value or no reading at all indicates a faulty capacitor.
• Visually inspect for bulging, leakage, or discoloration.
IMPORTANT NOTE: Check correct value from service and spare parts manual NOT what is on motor label as the capacitors change depending on the heater model
Additional Checks:
• Inspect for physical obstructions or debris in the fan housing
• Confirm ICS is receiving power and functioning correctly
• Check for blown fuses or tripped breakers
• Inspect for signs of overheating or burnt components
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Fan Does Not Reach Full Speed
Verify:
• Maximum speed setting
• Zoned operation speed
• Programmed time period speed
Voltage Check:
To verify correct voltage supply to the motor, follow the steps below:
Run Voltage Measurement:
Using a multimeter, measure the voltage across terminals “A” (Active) and “N” (Neutral) at the ICS (Integrated Control System).
This voltage corresponds to the motor’s run winding and will vary depending on the fan speed selected by the heater.
Start Voltage Measurement:
Additionally, measure the voltage across terminals “CAP” (Capacitor) and “N” (Neutral) at the ICS.
This voltage energizes the start winding via the capacitor and is typically higher than the voltage across “A” and “N”, especially during motor startup.
Note: The presence of voltage at “CAP” and “N” confirms that the start capacitor circuit is functioning. If there is no voltage present on these terminals, then strongly recommend testing the separate Room Fan Capacitor connected to CAP and CAP on the ICS.
Thermistor Function and High Temperature Troubleshooting in Supply Air Ductwork
To check the temperature at the thermistor
ON the MagIQtouch, while the heater is running enter the service screen and view thermistor temperature
Or you can turn on the information button (Settings – general – Status Information display) ***remember to turn off before leaving***
Overview
The thermistor installed in the supply air ductwork plays a critical role in monitoring air temperature and modulating the gas rate accordingly. It also controls the fan speed based on the supply duct temperature to ensure optimal heating performance and energy efficiency.
Fan Speed Modulation Based on Thermistor Temperature
The fan speed increases incrementally with the temperature detected by the thermistor:
< 41°C: Fan Speed 1
42°C: Fan Speed 2
43°C: Fan Speed 3
44°C: Fan Speed 4
etc...
50°C: Fan Speed 10
Ideal operating temperature at the thermistor after 10 minutes of heater operation on Fan Speed 10 with all outlets open is approximately 53°C.
Common Causes of High Thermistor Temperatures
If the thermistor temperature exceeds expected levels, it may indicate restricted airflow or installation issues. Below are common causes:
- Airflow Restrictions
- Insufficient outlets installed for the heater size, reducing room air circulation.
- User-selected low fan speed, limiting air movement and causing heat buildup.
- Blocked return air filter, restricting airflow back to the heater.
- Incorrect duct diameter for supply or return air, affecting air velocity and pressure.
- Return air grille undersized, limiting air intake.
- Ductwork Issues
- Tight radius bends or excessive duct length, increasing resistance and reducing airflow.
- Squashed or damaged ducting, impeding air movement.
- Thermistor Placement
- Too close to the heater may result in artificially high readings.
- Too far from the heater may prevent the thermistor from heating up correctly, affecting fan modulation.
- Recommendations
- Ensure ducting is installed according to manufacturer specifications.
- Verify the number and size of outlets match the heater’s capacity.
- Regularly inspect and clean return air filters.
- Confirm correct placement of the thermistor as per installation guidelines.
- Avoid sharp bends and long duct runs where possible.