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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers in the diagnostic table.

  1. 8:  This step ensures that the lower air temperature sensors operate properly. The LH and RH Heater Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
  2. 9:  This step ensures that the upper air temperature sensors operate properly. The LH and RH AC Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
  3. 11:  This action ensures that the internal fan of the inside air temperature sensor assembly is providing air flow across the internal sensor.
  4. 15:  Use the following table to determine that the recorded scan tool values are within range for the recorded probe temperatures.
Too Cold in Vehicle

Temperature °C Temperature °F Scan Tool Display
0-4 32-40 206-175 counts
5-9 41-49 194-161 counts
10-14 50-58 180-145 counts
15-19 59-67 166-133 counts
20-24 68-76 150-119 counts
25-29 77-85 136-106 counts
30-34 86-94 121-93 counts
35-39 95-103 107-81 counts
40-44 104-112 94-69 counts
45-49 113-121 83-59 counts
50-54 122-130 72-51 counts
55-59 131-139 63-44 counts
60-64 140-148 55-37 counts
Too Cold in Vehicle

Step Action Values Yes No
Schematic Reference:  HVAC Schematics  
Connector End View Reference:  HVAC Connector End Views  
DEFINITION: The temperature can not be adjusted, or heating is insufficient.
1 Did you perform the HVAC Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - HVAC Systems - Automatic 
2
IMPORTANT: If during this diagnostic procedure the HVAC control module is disconnected a recalibration of actuators must be performed to avoid misdiagnosis.
  1. Recalibrate actuators. Refer to Re-Calibrating Actuators .
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the Diagnostic Trouble Code (DTC) List .
Does the scan tool display any DTC B0229, B0414, B0424 or B3770?		 - Go to Diagnostic Trouble Code (DTC) List  Go to Step 3 
3
  1. Turn ON the ignition, with the engine OFF.
  2. Turn ON the HVAC control module.
  3. Place the mode switch in the PANEL position.
  4. Place the blower motor switch in each speed position.
Does the blower motor operate in any of the speed positions speed?		 - Go to Step 4  Go to Blower Motor Inoperative 
4 Does the blower motor operate in all desired speed positions? - Go to Step 5  Go to Blower Motor Malfunction 
5
  1. Place the recirculation switch in the ON position.
  2. Observe the recirculation door.
  3. Place the recirculation switch in the OFF position.
Does the recirculation door move from the recirculation position to the outside air position?		 - Go to Step 6  Go to Air Recirculation Malfunction 
6
  1. Start the engine.
  2. Place the mode switch in PANEL position.
  3. Place the A/C request switch in the ON position.
  4. Observe the A/C compressor clutch.
  5. Place the A/C request switch in the OFF position.
Does the A/C compressor clutch disengage?		 - Go to Step 7  Go to HVAC Compressor Clutch Does Not Disengage 
7 Perform the Heating Performance Diagnostic. Refer to Heating Performance Diagnostic .
Did you find and correct the condition?		 - Go to Step 28  Go to Step 8 
8 
  1. Start the engine.
  2. Wait until engine coolant temperature reaches its normal operating temperature.
  3. Place the mode switch to the Floor position.
  4. Place the drivers air temperature switch to the warmest position.
  5. With a scan tool, observe the right and left Heater Duct Actual and Heater Duct Desired parameters.
  6. Wait 3 minutes to allow the duct air temperature to stabilize.
Do both of the Heater Duct Actual parameter values increase within 15 Counts of the Heater Duct Desired parameter?		 - Go to Step 9  Go to Step 20 
9 
  1. Place the mode switch to the Panel position.
  2. Place the drivers air temperature switch to the warmest position.
  3. With a scan tool, observe the right and left AC Duct Actual and AC Duct Desired parameters.
  4. Wait 3 minutes to allow the duct air temperature to stabilize.
Do both of the AC Duct Actual parameter values increase within 15 Counts of the AC Duct Desired parameter?		 - Go to Step 10  Go to Step 20 
10 Check the air temperature sensors for proper installation.
Refer to the following procedures:
Did you find and correct the condition?		 - Go to Step 28  Go to Step 11 
11 
  1. Turn ON the ignition, with the engine OFF.
  2. Inspect for air flow through the inside air temperature sensor assembly by placing a 5 cm (2 in) square piece of paper over inlet of the inside air temperature sensor assembly.
Does the paper stay in place?		 - Go to Step 13  Go to Step 12 
12
  1. Turn the ignition OFF.
  2. Disconnect the inside air temperature sensor assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the inside air temperature sensor assembly control circuit of the inside air temperature sensor assembly with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 18  Go to Step 17 
13
  1. Turn ON the ignition with the engine OFF.
  2. Install a scan tool.
  3. Cover the sunload sensor.
  4. With a scan tool, observe the Left Solar Sensor and Right Solar Sensor parameters in the Body Control Module data list.
Does the scan tool indicate that the Left Solar Sensor and Right Solar Sensor parameters are greater than the specified value?		 220 Counts Go to Step 14  Go to Step 23 
14
  1. Place the temperature probe of the J 43600  near the inside air temperature sensor assembly.
  2. With a scan tool, observe the Inside Air Temp parameter in the Heating and Air Conditioning Data list.
Does the scan tool indicate that the Inside Air Temp parameter is within 3°C (5°F) of the probe temperature?		 - Go to Step 15  Go to Step 19 
15 
  1. Start the engine.
  2. Place the blower motor switch in the minimum speed position.
  3. Allow the engine to reach normal operating temperature.
  4. Place the blower motor switch in the maximum speed position.
  5. Place the left and right air temperature switches in the FULL HOT positions.
  6. Place the mode switch in the bi-level position.
  7. Wait 3 minutes to allow the discharge air temperatures to stabilize.
  8. With a scan tool, record the values of the following parameters in the Heating and Air Conditioning data list:
    • LH AC Duct Actual
    • LH Heater Duct Actual
    • RH AC Duct Actual
    • RH Heater Duct Actual
  9. With the temperature probes of the J 43600  , record the air temperatures near the following sensors:
    • The left upper air temperature sensor
    • The left lower air temperature sensor
    • The right upper air temperature sensor
    • The right lower air temperature sensor
Are the parameter values within the specified range for the recorded air temperatures?		 - Go to Diagnostic Aids Go to Step 16 
16
  1. Turn OFF the ignition.
  2. Disconnect the suspect air temperature sensor.
  3. Place the temperature probe of the J 43600  near the air temperature sensor.
  4. Record the probe temperature.
  5. Measure the resistance of the air temperature sensor. Refer to the Sensor Resistance Table (Primary HVAC) .
Does the resistance measure near the specified range?		 - Go to Step 24  Go to Step 20 
17 Test the inside air temperature sensor assembly control circuit of the inside air temperature sensor assembly for an open, a high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 24 
18 Test the ground circuit of the inside air temperature sensor assembly for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition		 - Go to Step 28  Go to Step 22 
19
  1. Turn OFF the ignition.
  2. Disconnect the inside air temperature assembly.
  3. Place the temperature probe of the J 43600  near the inside air temperature sensor assembly.
  4. Record the probe temperature.
  5. Measure the resistance of the inside air temperature sensor. Refer to the Sensor Resistance Table (Primary HVAC) .
Does the resistance measure within the specified range ?		 - Go to Step 24  Go to Step 20 
20 Test the signal circuit of the suspect air temperature sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 21 
21 Test the low reference circuit of the suspect air temperature sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 22 
22 Inspect for poor connections at the harness connector of the suspect air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 25 
23 Inspect for poor connections at the harness connector of the sunload sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 26 
24 Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 28  Go to Step 27 
25 Replace the suspect air temperature sensor. Refer to one of the following procedures:
Did you complete the replacement?		 - Go to Step 28  -
26 Replace the sunload sensor. Refer to Sun Load Sensor Replacement .
Did you complete the replacement?		 - Go to Step 28  -
27 Replace the HVAC control module. Refer to HVAC Control Module Replacement .
Did you complete the replacement?		 - Go to Step 28  -
28 Operate the system in order to verify the repair.
Did you correct the condition?		 - System OK Go to Step 2 
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