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A/c Question - 1991 Chevy 1-ton Dually

Question

On the dash for the htg & clg....the A/C letters are flashing. The A/C is in a non-operating position. Is the a meaning to the A/C letters to blink or flash?

Thanks

JB

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There are 4 bulletins for your problem.

 

ONE

 

Document ID# 223984

1991 Chevrolet Chevy K Pickup - 4WD

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A/C CONTROL HEAD FLASHES/ ERRATIC OPER. OF A/C CONTROLS #46-12-02 - (May 3, 1994)

SUBJECT: A/C CONTROL HEAD FLASHES OR ERRATIC OPERATION OF A/C CONTROLS (POLISH TERMINALS)

 

MODELS: 1988-94 CHEVROLET AND GMC TRUCK C/K MODELS 1990-94 CHEVROLET AND GMC TRUCK TOPKICK/KODIAK MODELS WITH C60 OR C69 AIR CONDITIONING

 

CONDITION:

 

A/C CONTROL HEAD FLASHES, PERFORMS ERRATICALLY OR MALFUNCTIONS.

 

CAUSE:

 

LIGHT SURFACE CORROSION ON THE CONTROL HEAD TERMINALS.

 

CORRECTION:

 

REMOVE THE A/C CONTROL HEAD AND WHILE HOLDING THE UNIT WITH THE TERMINAL CAVITY DOWN (TOWARD THE FLOOR) SO NO PARTICLES WILL FALL INSIDE ON THE CIRCUIT BOARDS, POLISH THE TERMINALS ON BOTH SIDES OF THE CAVITY WITH A LEAD PENCIL PINK ERASER. DO NOT USE AN INK ERASER OR OTHER ABRASIVE SUCH AS A SMALL WIRE BRUSH OR SANDPAPER, ETC. DOING SO WILL REMOVE THE TERMINAL COATING AND DEGRADE THE CONTACT SURFACE.

 

**PERFORMING THIS PROCEDURE, IN MANY CASES, WILL MAKE REPLACING THE CONTROL HEAD UNNECESSARY.** USING THIS PROCEDURE IN CONJUNCTION WITH THE A/C CIRCUIT DIAGNOSIS FOUND IN THE ELECTRICAL DIAGNOSIS MANUAL AND ESPECIALLY BEFORE REPLACING A CONTROL HEAD FOR ANY REASON IS RECOMMENDED.

 

AFTER POLISHING THE CONTROL HEAD TERMINALS, BUT BEFORE RECONNECTING, CHECK FOR PROPER TERMINAL CONTACT AS DESCRIBED IN THE APPLICABLE ELECTRICAL DIAGNOSIS MANUAL. IF CONTACT IS GOOD, APPLY DIELECTRIC GREASE (P/N 12345579) TO THE HARNESS CONNECTOR TERMINALS. PLEASE DO NOT APPLY GREASE TO THE CONTROL HEAD.

 

TWO

Document ID# 438412

1991 Chevrolet Chevy K Pickup - 4WD

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LOW CHARGE INDICATOR FLASHES DISCONNECT CHARGE DETECTION #93-1B-129 - (Sep 15, 1993)

SUBJECT: A/C LOW CHARGE INDICATOR FLASHES (DISCONNECT LOW CHARGE DETECTION FEATURE)

 

VEHICLES AFFECTED: 1991-93 C/K AND TOPKICK/KODIAK WITH A/C

 

Some owners of 1991-93 C/K and Topkick/Kodiak vehicles may comment that the A/C letter's in the middle of the control head face are flashing. The HVAC control system used on the above subject vehicles incorporates a low A/C charge warning system. If a low charge is detected, the control head will not allow the compressor to engage and the A/C letters in the middle of the control head face that usually signify A/C operation will blink.

 

The HVAC control head determines a low charge by monitoring the circuit from the pressure cycling switch. If the cycling switch will not allow the compressor to run more than 1.5 seconds, ten times in a row, the control head assumes a low charge and disables the compressor until reset.

 

On some vehicles, it has been found that the wire from the pressure cycling switch to the control head is sensitive to EMI (electro magnetic interference) and gives false compressor cycling information to the HVAC control head which then disables the compressor.

 

If you encounter a vehicle with the control head A/C indicator flashing the low charge signal but can find no reason for the flash using normal diagnostic procedures, including checking the wiring harness for chafing, remove the pressure cycling switch feedback wire from the control head connector. This process disables the A/C Low Charge detection feature, however, the customer will still be alerted to a low charge by excessive compressor cycling and poor A/C performance.

 

SERVICE PROCEDURE

 

1. Remove the instrument panel trim bezel.

 

2. Remove the A/C control head.

 

3. Disconnect the control head electrical connector.

 

4. C/K Models: Remove the dark green circuit 59 wire located in harness connector socket number one. Do not cut the wire, remove the terminal (Refer to the C/K Electrical Diagrams and Diagnosis Manual, under the air conditioning section).

 

5. Topkick/Kodiak: Remove the dark blue circuit 248 wire located in harness connector #C244 socket number one. Do not cut the wire, remove the terminal and tape (Refer to Topkick/Kodiak Electrical Diagrams and Diagnosis Manual, under the air conditioning section).

 

6. Fold the wire back along the harness and tape it so that it cannot short when the control head is installed.

 

7. Install the control head.

 

8. Install the instrument panel bezel.

 

 

THREE

Document ID# 250168

1991 Chevrolet Chevy K Pickup - 4WD

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LOW CHARGE INDICATOR FLASHES DISCONNECT CHARGE DETECTION #92-201-1B - (May 13, 1992)

Subject: AIR CONDITIONING LOW CHARGE INDICATOR FLASHES

 

Model and Year: 1991-92 C/K TRUCKS

 

Some owners of 1991-1992 C/K vehicles may comment that the A/C letters in the middle of the control head face are flashing. The HVAC control system used on 1991 and 1992 C/K vehicles incorporates a low A/C charge warning system. If a low charge is detected, the control head will not allow the compressor to engage and the A/C letters in the middle of the control head face that usually signity A/C operation will blink.

 

The HVAC control head determines a low charge by monitoring the circuit from the pressure cycling switch. If the cycling switch will not allow the compressor to run more than 1.5 seconds, ten times in a row, the control head assumes a low charge and disables the compressor until reset.

 

On some vehicles, it has been found that the wire from the pressure cycling switch to the control head is sensitive to EMI (electro magnetic interference) and gives false compressor cycling information to the HVAC control head which then disables the compressor.

 

If you encounter a vehicle with the control head A/C indicator flashing the low charge signal, but can find no reason for the flash using normal diagnostic procedures; including checking the wiring harness for chafing; remove the pressure cycling switch feedback wire from the control head connector using the service procedure outlined below. This process disables the A/C Low Charge detection feature, however, the customer will still be alerted to a low charge by excessive compressor cycling and poor A/C performance.

 

SERVICE PROCEDURE

 

1 . Remove the instrument panel trim bezel.

 

2. Remove the A/C control head.

 

3. Disconnect the control head electrical connector.

 

4. Remove the dark green circuit 59 wire located in harness connector socket number one. Do not cut the wire, remove the terminal (Figure 1).

 

5. Fold the wire back along the harness and tape it so that it cannot short when the control head is installed.

 

6. Install the control head.

 

7. Install the instrument panel bezel.

 

FOUR

Document ID# 437695

1991 Chevrolet Chevy K Pickup - 4WD

--------------------------------------------------------------------------------

LOW CHARGE INDICATOR FLASHES DISCONNECT CHARGE DETECTION #92-1-118 - (May 13, 1992)

SUBJECT: A/C LOW CHARGE INDICATOR FLASHES (DISCONNECT LOW CHARGE DETECTION FEATURE)

 

VEHICLES AFFECTED: 1991-1992 C/K TRUCKS WITH AIR CONDITIONING

 

Some owners of 1991-1992 C/K vehicles may comment that the A/C letters in the middle of the control head face are flashing. The HVAC control system used on 1991 and 1992 C/K vehicles incorporates a low A/C charge warning system. If a low charge is detected, the control head will not allow the compressor to engage and the A/C letters in the middle of the control head face that usually signify A/C operation will blink.

 

The HVAC control head determines a low charge by monitoring the circuit from the pressure cycling switch. If the cycling switch will not allow the compressor to run more than 1.5 seconds, ten times in a row, the control head assumes a low charge and disables the compressor until reset.

 

On some vehicles, it has been found that the wire from the pressure cycling switch to the control head is sensitive to EMI (electro magnetic interference) and gives false compressor cycling information to the HVAC control head which then disables the compressor.

 

If you encounter a vehicle with the control head A/C indicator flashing the low charge signal but can find no reason for the flash using normal diagnostic procedures, including checking the wiring harness for chafing, remove the pressure cycling switch feedback wire from the control head connector. This process disables the A/C Low Charge detection feature, however, the customer will still be alerted to a low charge by excessive compressor cycling and poor A/C performance.

 

SERVICE PROCEDURE:

 

1. Remove the instrument panel trim bezel.

 

2. Remove the A/C control head.

 

3. Disconnect the control head electrical connector.

 

4. Remove the dark green circuit 59 wire located in harness connector socket number one. Do not cut the wire, remove the terminal (Figure 1).

 

5. Fold the wire back along the harness and tape it so that it cannot short when the control head is installed.

 

6. Install the control head.

 

7. Install the instrument panel bezel.

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