GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B1348

Circuit Description

The HVAC control processor monitors the A/C low pressure switch signal circuit. If no voltage is detected on the signal circuit the HVAC control processor interprets that as low refrigerant pressure and disables the A/C compressor clutch. If voltage is detected on the signal circuit the refrigerant pressure is considered to be normal. The A/C low pressure switch is normally closed above 10 PSI.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC
    • The HVAC control processor detects that A/C has been requested.
    • The HVAC control processor does not detect voltage on the A/C low pressure switch signal circuit.

Action Taken When the DTC Sets
    • The HVAC control processor will not illuminate the Malfunction Indicator Lamp (MIL).
    • The message LOW REFRIGERANT--A/C OFF is displayed on the driver information center (DIC).
    • The A/C compressor clutch is disabled.

Conditions for Clearing the DTC
    • The DTC will become history if the HVAC control processor no longer detects a failure.
    • The history DTC will clear after 50 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. Verify the ambient air temperature and the refrigerant level before continuing with the diagnosis of the DTC.

    2.

  2. Verifies that battery voltage is supplied to the A/C low pressure switch.

    3.

  3. Verifies the condition of the fuse that supplies voltage to the A/C low pressure switch is good.

    4.

  4. Inspects the ignition 1 voltage circuit for a short to ground.

    5.

  5. Verifies the condition of the A/C low pressure switch.

    6.

  6. Inspects the A/C low pressure switch signal circuit for a high resistance or an open.

    7.

  7. Inspects the ignition 1 voltage circuit for an open.

    8.

  8. Inspects the A/C low pressure switch signal circuit for a short to ground.

    9.

  9. Perform the recalibration procedure for the HVAC control processor.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

Important: Verify that the ambient air temperature displayed on the driver information center is above 5.5°C (42°F).

Verify that the A/C system is properly charged. Refer to Refrigerant Recovery and Recharging and Refrigerant System Capacities in Heating Ventilation and Air Conditioning.

If the A/C system operates verify the performance. Refer to Air Conditioning (A/C) System Performance Test in Heating Ventilation and Air Conditioning.

  1. Install a scan tool.
  2. Turn ON the ignition, with the ignition OFF
  3. With a scan tool, observe the Low Refrig. Pressure Sw. parameter in the Body, Heating and Air Conditioning Inputs list.

Does the scan tool display that the Low Pressure Sw. parameter is Open?

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect the low pressure switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a test light probe the ignition 1 voltage circuit at the low pressure switch connector with the test lamp connected to ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 4

4

Important: For fuse location refer to Electrical Center Identification Views in Wiring Systems.

Test the fuse in the underhood electrical center with the test lamp.

Does the test lamp indicate that the fuse is good?

Go to Step 10

Go to Step 5

5

Test the ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

6

Install a 3-amp fused jumper wire between the ignition 1 voltage circuit and the low pressure voltage circuit at the A/C low pressure switch connector.

With a scan tool, observe the Low Refrig. Pressure Sw. parameter.

Does the scan tool display that the Low Pressure Sw. parameter is Open?

Go to Step 7

Go to Step 8

7

Test the A/C low pressure switch signal circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

8

Inspect for poor connections at the A/C low pressure switch. 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 14

Go to Step 12

9

Inspect for poor connections at the harness connector of the HVAC control processor. 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 14

Go to Step 13

10

Repair the open in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

11

Test the A/C low pressure switch signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

12

Replace the A/C low pressure switch. Refer to Air Conditioning (A/C) Low Pressure Switch Replacement in Heating Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 14

--

13

Important: Perform the recalibration procedure for the HVAC control processor .

Replace the HVAC control processor. Refer to HVAC Control Processor Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK