Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There has been a service bulletin for that type of concern. Here is what it states.
BULLETIN NUMBER: 93-1B-109
SECTION: 1B Air Conditioning
CORPORATE REFERENCE NUMBER: 261201R
DATE: August 1993
THIS BULLETIN IS BEING REVISED TO INCLUDE THE 1993 MODEL YEAR AND THE TOPKICK/KODIAK MODELS.
Some owners of 1991-93 C/K and Topkick/Kodiak vehicles may comment that the A/C letters 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.
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).
Remove the dark blue circuit 248 wire located in harness connector # XXXXX 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).