NO AIR CONDITIONING COOLING CODE 66 SET. Buick Park Avenue 1992

SUBJECT: NO A/C OR COOLING

VEHICLES AFFECTED: 1991-93 C, H, W AND U-VANS EQUIPPED WITH 3800 (VIN CODE L AND 1 - RPOS L27, L67) ENGINES

Owners of some 1990-93 C, H, W and U-vans equipped with either the 3800 engine (VIN L) or the 3800 S/C (VIN 1) that have comments of "no A/C" or "no cooling", remember to check for ECM Code 66 first. Code 66 is stored in the ECM to protect the compressor from engaging when the system is low on refrigerant. The ECM monitors the A/C request line (CKT 67) for a switching voltage controlled by the pressure cycling switch. If voltage is present at the ECM for less than 1.5 seconds, 10 successive times, Code 66 will set and the ECM will not provide a ground for the A/C relay (CKT 366) for the rest of the ignition cycle. If Code 66 is set 3 times, the ECM will never engage the A/C relay until Code 66 is cleared. A Code 66 will not turn on the "Service Engine Soon" light and can only be cleared with a scan tool or by disconnecting the power supply to the ECM.

Code 66 was designed to protect the compressor from damage by preventing its operation when the system was low on refrigerant. The ECM assumes the system is low on refrigerant if it sees the pressure cycling switch cycling more rapidly than normal, just like a system will do when it is low on refrigerant. Based on this rapid cycling, the ECM sets Code 66 and will not provide a ground to the A/C clutch relay. CAMS and Tech 1 will also be unable to command the A/C clutch relay on when Code 66 is set. Do not replace the ECM if it fails to ground the A/C clutch relay, make sure there is no Code 66 set first. The A/C compressor will start working when a new ECM is installed, as disconnecting the ECM clears the codes. However, the problem has not been found. When Code 66 is set, follow the service manual procedure in Section 6E3 of the Service Manual.

On 1991-93 C and 1992-93 H cars with Automatic Air Conditioning (C68), once Code 66 is set in the PCM, it is also set in the Heater-A/C Programmer. Code 66 in the programmer will not provide a ground for the A/C relay (CKT 366) for the rest of the ignition cycle or until Code 66 is cleared from memory, through on-board diagnostics.

On 1991 C cars Code 66 will not display when entering diagnostics on the HVAC system. Code 66 is masked in the software on all 1991 C cars. Both PCM and Heater-A/C codes must be cleared to allow the compressor clutch to engage.

On 1992-93 C and H cars Code 66 will be displayed on the Heater-A/C diagnostics. The control assembly display will flash for 2-3 seconds when the ignition switch is turned to run and the A/C is on. This will be stored and displayed on the A/C control assembly.

Cams and Tech 1 will also be unable to turn the A/C clutch relay on when Code 66 is set. DO NOT REPLACE THE PCM IF IT FAILS TO GROUND THE A/C CLUTCH RELAY. First make sure Code 66 has not been set. Always remember to clear both PCM and Heater-A/C codes after diagnosis to ensure A/C clutch operation.

Important: If a new PCM is installed without correcting the original problem, the A/C compressor will work until Code 66 is set. Remember, the new PCM does not have any codes stored when it is installed.

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.