Auxiliary Heater Inoperative 1998

The HEAT switch completes a circuit to pin C4 of the HTCM when closed. This input is used by the HTCM to determine whether to operate the Refrigerant/Heat Pump (R/HP) compressor as a heat pump or an A/C compressor, or to activate the Auxiliary Fuel-Fired Heater. If the ambient temperature is between 2°C (35.6°F) and 16°C (60.8°F) and this switch is closed, the HTCM will operate the R/HP compressor as a heat pump. If the temperature is below 2°C (35.6°F), the HTCM will inhibit the R/HP compressor operation and activate the Auxiliary Fuel-Fired Heater. Above 16°C (60.8°F) turning this switch on will inhibit A/C operation. Run0 voltage (approximately 13.8 volts) is provided to the HVAC Mode Select switch through the HVAC 20A fuse when the ignition is ON. The HVAC Mode Switch supplies voltage to the HEAT switch at pin 2 in any position except OFF. If the HVAC fuse is open, the blower motor, and the A/C Request to the HTCM will be inoperative as well. When the HEAT switch is closed, voltage is supplied to the LED in the switch which is grounded at pin 4 and to the HTCM through pin 3. When the HTCM receives a auxiliary heater request input from the heat switch, the HTCM checks the ambient temperature, or the state of the Auxiliary Heater Service Request Input to determine whether or not to energize the Auxiliary Heater Relay. If the temperature conditions are correct, or the Auxiliary Heater Service Request input is High, the HTCM will provide a ground to the relay energizing it. Once the relay is closed, battery voltage is applied to the Switch Signal Input CKT 925 (DK BLU) wire at pin C of the Auxiliary Heater. This starts the Auxiliary Fuel-Fired Heater. As long as this input is present on pin C, the Auxiliary Fuel-Fired Heater will continue to operate. Once the input is removed, the Auxiliary Fuel-Fired Heater will turn off. However, the heater must complete it's purge cycle to clear out any residual diesel fuel, before it will shut off completely.

1. Start (0 seconds)

•	Water pump starts working, humming noise of waterflow through heater is noticeable)

•	Blower starts working in part load, humming noise, high frequency will be noticeable)

•	Glow pin starts pulsed glowing (Relay's ticking can be heard from electronic unit)

2. After 35 seconds

•	Fuel metering pump starts pumping (2-4 ticking pulses per second can be heard)

•	The ticking noise will be louder during initial start or after a new installation and turns quieter as soon as the fuel pipe from the tank to the fuel pump gets bled

3. After 65 to 120 seconds

•	Within 120 seconds from switching on, the flame detector will recognize combustion and switch off the glow pin (Relay's ticking from the Electronic Unit will disappear). Typically it takes 30-60 seconds after the fuel pump has started.

•	A burning noise (howling with deep frequency) will be heard.

4. After 85 to 140 seconds

•	The heater is working in partial load for 20 seconds. (Water pump is on with humming noise, blower is on with humming high frequency noise, fuel pump is ticking at 2 pulses per second).

•	The heater continuously to full load for 60 seconds. (Water pump is on with humming noise, blower gets a little bit louder with the this high frequency humming noise, the fuel pump will tick with approximately 4 pulses per second).

•	The deep frequent burning noise of the heater gets a little bit louder. The unit is working in full load.

5. After 300 seconds (5 minutes)

•	The vehicles cabin heater blower should provide warm air though the selected vents

•	The air should be heated to approximately 65°C (150°F)

6. After 480-600 seconds (8-10 minutes)

•	The heater will turn to part load

•	The blower and burner noise will decrease and the fuel pump will reduce to 2 pulses per second.

7. Switching off

•	The heater goes through a purge cycle to eliminate any excess fuel and to prevent the orifice from clogging.

•	Fuel pump turns off, blower and water pump stay on for 2 minutes.

A potentiometer can be connected in place of the Ambient Air Temperature (AAT) sensor to simulate the temperature ranges. It is recommended, however, that the system be tested in the environment for which the symptom exists.

Inserting a fuse into the Auxiliary Fuel-Fired Heater Service Port will allow operation of the Auxiliary Fuel-Fired Heater at any ambient temperature.

The following describes normal operation of the Auxiliary Fuel-Fired Heater: