WHITE SMOKE CONTROLLER AND AIR HEATER (OPERATION & SERVICE)
SUBJECT: AIR HEATER OPERATION AND TROUBLESHOOTING
MODELS: 1988 C7 AND S7 W/8.2L
The air inlet heater was previously released on the 230 H.R Federal engine to reduce white smoke at start-up and most recently on the 225 H.P. California certified engine to improve cold weather startability and to reduce white smoke on both the 225 California and 230 H.R Federal certified engine.
The former air heater controller, P/N 8926618, used on the 230 H.P. Federal certified engine has been superseded with the new controller P/N 23503679.
There are no physical external differences between the two engines (model 4087-7336) nor the controller. This also includes the coolant sensor (P/N 8927122), on pressure switch (P/N 8927121) and heater element (P/N 8926619). There is, however, a change to the engine s sequence. To improve cold weather startability and reduce white smoke at start up, the air heater controller has been modified to add a pre-heat cycle.
IMPORTANT: FOR COMPONENT DESCRIPTIONS, OPERATION AND TROUBLESHOOTING OF FORMER AIR HEATER SYSTEM, REFER TO SERVICE INFORMATION NUMBER 2-8.2L-86 PUBLISHED BY DETROIT DIESEL ALLISON IN FEBRUARY, 1986.
Components
The air heater system consists of five (5) major components supplied with the engine:
1. Heater Controller/Wire Harness (P/N 23503679)
The heater controller is mounted on the air inlet crossover housing on the right-bank side of the engine. It controls the pre-heat cycle and the regular heat cycles of the heater element and depends on input from the coolant sensor and the oil pressure switch. The controller has a built-in Circuit board which allows the heater to stay on for 30 seconds for pre-heating when the ignition is turned to the on position and turns the heater off when the ignition switch is turned to the start position. It also allows the heater to stay on for a maximum of six (6) minutes during the regular heating cycle after the engine is operating. The controller also houses the heater solenoid, which supplies power to the heater element.
2. Heater Element (P/N 8926619)
The heater is a 12-volt, 1.2 kilowatt, self-contained heating element mounted in the air inlet housing, close to the turbo-charger.
3. Coolant Sensor (PIN 8927122)
The coolant sensor is mounted in the off cooler housing where it senses the coolant temperature. Once the coolant temperature reaches 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius), the sensor signals the controller to turn off the power to the heater. The system will not work unless the coolant temperature is below 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11. 12 degrees Celsius).
4. Oil Pressure Switch (PIN 8927121)
The oil pressure switch is also located in the oil cooler housing. This normally open switch allows the heater to operate for the regular heat cycle when the engine is running and oil pressure reached 50 psi plus or minus 5 psi (345 kPa plus or minus 34.5 kPa).
5. Gasket, Air Heater (P/N 8926620)
Two gaskets are required, one on each side of the air heater.
Operation
Pre-heat Cycle: When the ignition switch is turned to the run position the coolant temperature is below 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius) and the heater has not timed out for six (6) minutes in the regular heat cycle, the controller is programmed to engage the heater solenoid and supply power to the heater element. The heater will operate for as long as 30 seconds prior to the ignition switch being moved to the start position. There are three (3) ways for the pre-heat cycle to end:
1. The ignition switch is moved to the start position.
Turning the switch to the start position shuts down the pre-heat cycle. When the engine starts, switch is returned to the run position, on pressure exceeds 50 psi plus or minus 5 psi (345 kPa plus or minus 34.5 kPa) and coolant temperature is below 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius) the heater will operate/run its regular cycle of approximately six (6) minutes.
2. The ignition switch is turned off.
This shuts down the pre-heat cycle.
3. Engine coolant temperature is above 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius)
Regular Heat Cycle: If the key is in the run position after starting engine, oil pressure is at 50 psi plus or minus 5 psi (345 kPa plus or minus 34.5 kPa), coolant temperature is below 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius), and the heater has not been timed out for 6 minutes, the controller will engage the heater solenoid and supply power to the heater element. Once on, there are three (3) ways for the air inlet heater to turn off.
A. The ignition key is turned off.
Turning off the ignition key shuts down the heater system. If the key is turned off before the system times out (6 minutes on), and turned back on, the heater win operate for the remainder of the 6 minutes. If the coolant temperature is below 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius), at the end of six (6) minutes the heater will recycle.
B. The coolant temperature reaches 100 plus or minus 20 degrees Fahrenheit (37.8 plus or minus 11.12 degrees Celsius). When the coolant reaches this temperature, the coolant sensor shuts off the power to the heater element. The system stays off as long as the coolant temperature is above this range.
C. The system is on for more than 6 minutes. he heater controller limits the amount of time the heater is on to six (6) minutes. After the six (6) minute period, the heating system will turn back on again only if the coolant has not reached 100 degrees Fahrenheit (37.8 degrees Celsius).
Troubleshooting
If for any reason the system malfunctions, the engine will start start and run. The only concerns may be the amount of "white smoke" present and the possible requirement of the use of another starting aid. If a malfunction occurs in the heater system, make no assumptions that the primary cause lies in the heater system. Use a systematic approach by looking for the most obvious things first. The following troubleshooting guide and diagnostic procedures should make your job easier.
There are normally three symptoms that Win occur when there is a malfunction in the heater system, which are: 1) Heater stays on longer than the allotted time during either or both cycles, 2) The heater does not come on or 3) Heater causes excessive drain on batteries.
Heater stays on longer than allotted time - Both cycles
1. Replace the air heater controller/harness (P/N 23503679)
Heater does not come on
1. Should this symptom occur, check for the following:
- A defective controller
- A defective oil pressure switch (regular heater cycle only)
- A defective coolant sensor
- A defective heater element
Controller check/regular and pre-heat cycles
CAUTION:
TO AVOID PERSONAL INJURY (BURNS) MAKE SURE COOLANT TEMPERATURE IS BELOW 100 DEGREES FAHRENHEIT (37.8 DEGREES CELSIUS) BEFORE PERFORMING THIS TEST.
Pre-Heat Cycle
With the help of a co-worker, tum the ignition switch to the "on" position and feel the heater solenoid for a "click. The cover must be removed from the controller to gain access to the solenoid. The click indicates that the solenoid is working properly. If no click is felt when switch is turned to the on position, proceed as follows:
1. Disconnect the 4-prong connector at the controller assembly. Attach a voltmeter between terminal "D" of the vehicle end of the wiring harness and ground.
2. With the key in the "on" position, a reading of 12 volts should be evident.
3. If no reading is noted, inspect the vehicle's wiring system for a blown fuse, cut/broken wire or poor connection.
4. If a reading of 12 volts is noted, reconnect the 4-prong connector.
5. Disconnect the wiring harness at the coolant sensor. With a small "jumper" wire, connect the two (2) terminals on the controller end of the wiring harness.
6. With the help of a co-worker, turn the ignition switch to the "on" position and feel the heater solenoid for a "click".
7. If the click is felt, the temperature is above 100 degrees Fahrenheit (37.8 degrees Celsius) or coolant sensor is defective.
8. Replace the coolant sensor with a new one and reconnect the wiring harness.
9. Turn the ignition switch to the "on" position and check for the click in the solenoid. If the solenoid clicks, then the original coolant sensor was defective.
Regular Heat/Run Cycle ---------------------- If the heater does not come on when the engine is started and is running or if the heater shuts down after the 30 second pre-heat cycle proceed as follows:
Heater Does Not Come On When Engine Is Started And Running
A. Follow steps 1-9 with the only exception being that the engine is started and running.
If the system does not work with the coolant sensor jumped, proceed as follows:
B. Leave the coolant sensor lead jumped.
C. Disconnect and jump the oil pressure switch.
D. With the help of a co-worker, start the vehicle and feel for the "click" in the solenoid.
E. If the solenoid clicks, then the pressure switch should be replaced.
F. If the coolant sensor and pressure switch are both jumped and the solenoid does not click, then the controller is defective.
Heater Shuts Down After 30 Second Pro-Heat Cycle
If the heater shuts down after the 30 second Pre-Heat cycle the cause is either coolant temperature above 100 degrees Fahrenheit (37.8 degrees Celsius), a defective oil pressure switch or defective controller. To troubleshoot for this malfunction follow steps B - F.
Heater Element Check
If, during the inspection of the controller, no malfunction can be found and the heater still does not seem to work, the heater element might be defective. Inspect the heater element as follows:
1. With the coolant temperature below 100 degrees Fahrenheit (37.8 degrees Celsius) or with the coolant sensor lead jumped, measure voltage on the controller side of the heater.
2. If no reading is recorded, then check for voltage across the solenoid. The best way to do this is with a test light. Check both sides of the heater solenoid. If the light does not work on the heater side of the solenoid, but works on the opposite side, then the solenoid is defective and the complete controller should be replaced. If the light does not work on either side of the solenoid, then the power lead to the solenoid is defective and should be repaired.
3. If a voltage was measured on the controller side of the heater element, disconnect the 8AWG (American Wire Gage) wire on the controller side of the heater element (key in the OFF position). Using an ohmmeter, measure the resistance across the two (2) terminals of the heater. The reading should be .08 -.12 ohms.
a. If the meter reads an infinite resistance (open circuit), then the heater element is defective and should be replaced.
b. If the ohmmeter records the correct resistance, then the 8AWG lead from the heater element to ground should be checked.
Coolant Sensor Check
The coolant sensor used in the air heater system is a PTC thermistor sensor with a nominal resistance of 100 ohms @ 100 degrees Fahrenheit (37.8 degrees Celsius). To inspect the coolant sensor, proceed as follows:
1. Remove the sensor from the oil cooler housing and place the sensor in a container of water.
2. Connect an ohmmeter across the terminals of the sensor (a digital meter will work the best).
3. Place a thermometer in the container of water and heat the water gradually.
4. Record the temperature and resistance of the sensor. Replace the sensor if resistance is not within the following limits:
TEMPERATURE RESISTANCE (ohms) ----------- ----------------- Fahrenheit Celsius ---------- ------- 80 (26.7) 878 plus or minus 100 90 (32.2) 969 plus or minus 100 100 (37.8) 1000 plus or minus 100 110 (43) 1375 plus or minus 100 120 (49) 2355 plus or minus 100
A rough check of the coolant sensor can also be made without removing the sensor from the oil cooler housing. Use the following procedure:
A. With the cooling system at room temperature (cold engine), disconnect the sensor lead and connect an ohmmeter across the sensor.
B. Start the engine and let idle.
C. Watch the ohmmeter as the temperature of the coolant rises. The resistance of the sensor should increase to the values shown above. If it does not, the sensor should be replaced.
Oil Pressure Switch Check
To determine if the oil pressure switch is working correctly, proceed as follows:
1. With the engine stopped, disconnect the lead to the off pressure switch in the oil cooler housing.
2. Connect a digital ohmmeter across the oil pressure switch leads.
A. With the engine stopped (0 psi, 0 kPa oil pressure), the ohmmeter should read infinite resistance (open circuit).
B. Start the engine and increase the speed until the oil pressure is 50 psi (345 kPa). At this point, the resistance across the oil pressure switch should be 0 ohms (closed circuit).
C. If either of these conditions are not met, the oil pressure switch should be replaced.
Wiring Schematic For Air Heater System
Figure 2 provides a wiring schematic of the 230 H.P. 8.2L engines air inlet heater system. This will serve as an installation aid during retrofit and as a reference when troubleshooting the air heater system.
Special Instructions
1. The negative terminal of the heater must be grounded to the engine using at least 8AWG wire.
2. The positive terminal of the solenoid must be connected to a 12 volt, continuously hot lead from the battery or starter of the vehicle. This wire must also be at least 8AWG wire.
3. Use terminal "B" of the four-pin weatherpack connector for a dash light; "D" should be wired to the ACC of the vehicle's ignition switch.
4. All wiring should be 16AWG for these connections, unless noted otherwise.
5. Optimally, the ground should be brought back to the engine.
6. The wiring insulation should be capable of withstanding 250 degrees; Fahrenheit (125 degrees Celsius).
The wiring should be securely fastened so that chaffing and wear on the insulation is minimized.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
