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Components
The following image and list outlines the typical direct fired heater components and their functions.
1. Gas Inlet – Main gas supply connection
2. Motor Starter – Contactor with overload protection to start and protect motor.
3. Freeze-Stat Thermostat (Optional) – De-energizes blower motor if the discharge air
temperature falls below the set point.
4. Cooling Interlock Relay (Optional) – Energizes power to cooling circuit on call for cooling.
5. Inlet Gas Pressure Tap – Inlet gas pressure should be measured here.
6. Combination Gas Valve - A combination of redundant solenoid valves, pilot valve and gas
regulator built into one unit.
7. Pilot Tubing – Pilot tube connection to combination gas valve.
8. Manual Reset High Temperature Limit – Safety device that prevents the heater from
overheating.
9. Maxitrol Modulating Amplifier - Regulates temperature by modulating gas valve
10. Power Transformer – Installed when motor voltage > 120V. Used to provide 120V service to
controls.
11. Circuit Breaker – Protects electrical components from high current spikes.
12. Terminal Strip – Central location to terminate control wiring. Should be used for troubleshooting.
13. Control Transformer – 120V primary; 24V secondary control transformer.
14. Low Pressure Airflow Probe – Measures profile pressure downstream of burner.
15. High Pressure Airflow Probe – Measures profile pressure upstream of burner.
16. Modulating Gas Valve – Modulates gas flow to burner to provide proper air temperature.
17. Manifold Gas Pressure Tap – Manifold gas pressure should be measured here.
18. Flame Safety Control – Initiates and monitors flame.
19. Airflow Switch – A safety device insuring proper air flow during burner operation.
20. Ignition Transformer – Produces high voltage spark to ignite flame.
21. Intake Air Thermostat – De-energize heating circuit when intake air exceeds set-point.
22. Damper Actuator – Motor containing end switch that opens intake damper.
23. Manual Gas Shut-Off Valve Allows gas flow to burner to be shut off to leak test gas train
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