GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2004 🢒 Isuzu MD F-Series 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Too Cold in Vehicle

Test Description

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

  1. This checks for proper cooling system operation.

    2.

  2. The voltage will vary between 0-12 volts during normal operation. The HVAC control module connector must be connected during this step.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

DEFINITION: Temperature can't be adjusted or heating insufficient.

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2
  1. Turn ON the ignition, with the engine OFF.
  2. Place the blower control in each speed position.

Does the blower motor operate in any of the speed positions?

--

Go to Step 3

Go to Blower Motor Inoperative

3

Does the blower motor operate in each speed position?

--

Go to Step 4

Go to Blower Motor Malfunction

4

Turn the blower motor fan ON and select an air outlet mode.

Does air flow out of the selected HVAC outlet ducts?

--

Go to Step 5

Go to Air Delivery Improper

5

Inspect the cooling system for the following conditions:

    • A low coolant level
    • A loose or worn accessory drive belt
    • A leaking radiator hose or heater hose
    • A kinked radiator hose or heater hose
    • Missing radiator filler cap pressure seal
    • A missing radiator cap pressure seal
    • A leaking radiator cap

Did you find and correct the condition?

--

Go to Step 20

Go to Step 6

6
  1. Start the engine.
  2. Place the mode switch in the vent or heat positions.

Does the A/C compressor operate?

--

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 7

7
  1. Place blower switch in any position but OFF.
  2. Place mode switch to HEATER position.
  3. Place the air temperature switch from the coldest position to the warmest position.
  4. Measure the voltage from the signal circuit of the air temperature actuator to a good ground.

Does the voltage measure within the specified values with a smooth transition between COLD to HOT?

0.5-4.5 V

Go to Step 10

Go to Step 8

8
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect air temperature actuator.
  3. Measure the voltage from the 5 volt reference circuit of the air temperature actuator to a good ground.

Does voltage measure near the specified value?

5 V

Go to Step 9

Go to Step 13

9

Inspect the air temperature door and the air temperature actuator for the following conditions:

    • A misaligned air temperature actuator
        Refer to Air Temperature Actuator Replacement .
    • Broken or binding linkages
    • A broken or binding air temperature door
    • An obstruction that prevents the air temperature door from operating within its full range of motion

Did you find and correct the condition?

--

Go to Step 20

Go to Step 10

10

  1. Place the blower switch in any position but OFF.
  2. Place the mode switch to HEATER position.
  3. Place the air temperature switch from the coldest position to the warmest position.
  4. Measure the voltage from the door control A circuit and door control B circuit of the air temperature actuator.

Does the voltage measure near specified value?

1-12 V

Go to Step 16

Go to Step 11

11

Test the door control A circuit of the air temperature actuator for an open, a high resistance, a short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 12

12

Test the door control B circuit of the air temperature actuator for an open, a high resistance, a short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 13

13

Test the 5 volt reference circuit of the air temperature actuator for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 14

14

Test the signal circuit of the air temperature actuator for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs a in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 15

15

Test the low reference circuit of the air temperature actuator for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 17

16

Inspect for poor connections at the harness connector of the air temperature actuator. 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 20

Go to Step 18

17

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 20

Go to Step 19

18

Replace the air temperature actuator. Refer to Air Temperature Actuator Replacement .

Did you complete the replacement?

--

Go to Step 20

--

19

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

--

Go to Step 20

--

20

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2