A/C CONTROL HEAD LOCK-UP DUE TO LOW REFRIGERANT (DIAG.)

SUBJECT: A/C CONTROL HEAD LOCKS UP (LOW REFRIGERANT DETECTION FUNCTION)

MODELS: 1991 C/K LIGHT DUTY TRUCKS WITH C60 AIR CONDITIONING

The above subject vehicles have electric control heads and may experience a control head lock up due to the low refrigerant detection system which is new for 1991. To unlock the control head, disconnect the battery and reset the controller memory.

The controller monitors the state of the low pressure cycling switch if the compressor has been activated. In addition it measures the duration of the time the compressor is engaged. If the compressor is engaged for less than 1.5 seconds before disengaging for 10 consecutive cycles the controller will turn off the compressor. The compressor will remain off until correction of the low charge symptom has been performed and the battery disconnected to reset the memory.

The A/C indicator on the controller will also flash for a period of 2 minutes and then turn "off" when the low charge condition has been detected. It will also flash at every ignition cycle for 2 minutes until the servicing has been performed and the battery disconnected to reset the memory.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.