Heater Trouble Diagnosis

South Wind (Steward Warner) Models 8240 through 8472 Series

The following are just basic troubleshooting tips. Most problems will be identified using the following steps. For detailed servicing or overhaul see the following manual. For 8240 thru 8259 series see service manual form no 09-998. For 8472 series see form no. 09-1015.

  1. Test Equipment needed:
    1. Basic hand tools
    2. Voltmeter
    3. Temperature monitor 0-500
    4. Fuel pressure gauge 0-50 psi
    5. Auxiliary power supply
  2. Identifying features of the South Wind (Stewart Warner) 8240 thru 8472 service heater
    1. . 2” exhaust
    2. Combustion air blower mounted separate from the heater with a fuel pump on the end of the motor
  3. General: 35,000-45,000 BTU heaters
  4. Electrical:
    1. 24 Volt applications
    2. Terminal strip numbered “4, 5, 6, 7, 8, 10”
    3. Normal heater operation for all models with solid-state ignitions will provide power at the heater terminal strip numbers “4, 5, 6, 7, 8, and 10.” As the heater reaches preset temperature, power will remain at all but “8” on non-pressurized aircraft until heat is again required at which time power will again be present at terminal “8”. Pressurized aircraft will interrupt power at terminal “7” for heat control.
      1. Early heaters 8240A, 8259A and DL with mechanical ignition will have no wires on “10” but still interrupt power to “8” for heat control
  5. Basic requirements for heater operation:
    1. . There are five basic requirements for a combustion heater to function.
      1. Electrical power
      2. Ignition
      3. Fuel
      4. Combustion air
      5. Ventilating air
    2. If any of these are absent or out of tolerance the heater will not operate correctly
  6. Trouble Diagnosis: (The following basic troubleshooting steps are in order of ease of inspection and are the most common cause of failure)
    Note: It is suggested that one person operate the heater controls and another person perform the checks at the heater.
    1. Common Problems
      1. Most common problems in order of their probability are:
      2. Fuel pressure (22-30 psi) See step 4.
      3. Ignition (fuel dripping from heater drain or exhaust) See step 3.
      4. Air flow switch See step 2.
    2. b. Problem 1 - Heater inoperative or intermittent
      1. Step 1 - Ventilation Air
        1. Verify air flowing from distribution points in the aircraft.
          1. If no air flow:
            1. Check for voltage on the heater terminal strip numbered “5.”
              1. Power present at terminal 5 means vent blower is bad.
              2. No power present, follow to source of power and correct. Possibly circuit breaker for ventilation blower, heater switch, or broken wire.
      2. Step 2 - Combustion air and electrical power to heater circuit troubleshooting
                1. Verify air is flowing from exhaust of heater. Any airflow is sufficient for preliminary inspection.
                  1. Airflow from exhaust:
                    1. If power is present at heater terminal #6 but not at terminal #7 then airflow switch is sticking or bad.
                      1. Clean only with electrical contact cleaner. Do not lubricate.
                  2. No Air flow from exhaust:
                    1. Check for power at terminal number “6” on the heater terminal strip.
                      1. If power is present and no air flow from the exhaust, combustion air blower is bad.
                      2. If power is not present at terminal “6” the overheat switch has probably activated. Reset. (See wiring schematic at end of troubleshooting.)
                        1. The most common cause of overheat switch activation is caused by the pilot not allowing for the heater to cool off prior to shutting down the aircraft.
      3. Step 3 – Ignition troubleshooting (Note wiring schematic)
        1. Verify there is power to the ignition unit from heater terminal number “10.” (on very early heaters 8240A, 8259A & DL with mechanical ignitions it will be terminal number “6” that supplies power to ignition. There will be no wires on “10.”)
          1. If power is present at the ignition unit:
            1. Turn the heater off and remove the igniter from the heater and reinstall it in the lead.
            2. Allow the igniter to lie against the heater to provide grounding to the case. Make sure the igniter end disc is not touching ground. Only the main body should be grounded.
            3. Turn the heater back on and observe the disc on the end of the igniter.
              1. A bright blue consistent spark should be visible.
              2. Weak, absent of a single spark indicates a faulty ignition and it should be replaced.
          2. If power is not present at the ignition unit:
            1. If power is at terminal number “6” and not at “10” (early heaters 8240A, 8259A & DL with mechanical ignitions power on “6” but not at ignition) the airflow switch is faulty.
      4. Step 4 – Fuel troubleshooting
        1. Remove the fuel pump cover and visually inspect the fuel box below the pump for brass particles.
          1. If brass particles are present replace the pump.
          2. Also turn the heater on and verify the coupling between the motor and pump are complete and pump is turning. Replace pump if coupling is sheared.
        2. “Tee” in 0-50 PSI fuel pressure gauge between the fuel pump and heater.
          1. Turn the heater on and temperature control in full hot.
          2. Verify fuel pressure is above 22 psi with heater calling for heat.
          3. If less than 22 psi with heater in operation replace pump. Fuel pressure must be more than 22 psi for proper operation especially at altitude.
        3. If fuel pump and pressure is good check the exhaust for fuel smell.
          1. No fuel smell at exhaust, no fuel dripping from heater drain, or exhaust.
            i. Check for power at terminal “8” (pressurized aircraft “7”).
            1. If no power at “8” (pressurized aircraft “7”) but if power is at “7” (pressurized aircraft power at “8”) the thermostat is not working. Refer to wiring schematic.
              1. The thermostat can be checked by placing a jumper across terminals seven and eight. If heater operates with jumper replace thermostat.
          2. Fuel smell at exhaust or fuel dripping:
            1. If all previous steps check out good the problem is most likely inside the heater. (i.e. fuel solenoid or nozzle contamination)
            2. This will require removal of the heater from the aircraft for servicing. We recommend at this point sending the heater and combustion air blower/fuel pump assembly to C&D Associates Inc. for evaluation/repair

View the troubleshooting chart (pdf)


Disclaimer: The following info is to assist our customers. We accept no responsibility for the outcome of the preceding procedures.