A/C - Slow to Cool in Hot/Humid Conditions

Bulletin No.: 04-01-38-019A

Date: June 07, 2005

TECHNICAL
Subject:
Intermittent Slow to Cool HVAC Performance Concerns in High Ambient Temperatures and/or High Humidity Conditions After Start Up, Especially at Low Engine Speeds (Install New Engine Cooling Fan Clutch)

Models:
2004-2005 Buick Rainier
2002-2005 Chevrolet TrailBlazer Models
2002-2005 GMC Envoy Models
2002-2004 Oldsmobile Bravada
2005 Saab 9-7X

Supercede:

This bulletin is being revised to provide repair information for this customer concern. Please discard Corporate Bulletin Number 04-01-38-019 (Section 01 - HVAC).

Condition

Some customers may comment on slow to cool Air Conditioning (A/C) performance or high A/C outlet temperatures after start up or that the A/C system is not cooling sufficiently, especially in high ambient temperatures. This may be an intermittent condition and the performance of the Heating, Ventilation and Air Conditioning (HVAC) system may not meet customer expectations.

Cause

This condition may be caused by the response of the Electro-Viscous (EV) fan clutch and can be related to airflow across the condenser. This low A/C system performance can occur for longer periods of time if the vehicle is allowed to idle or is driven in low speed conditions. The response of the EV fan clutch will affect A/C system performance. As higher road speeds are attained, the increased airflow across the condenser will usually improve A/C system performance and the response of the EV fan clutch. This condition may be more evident after the vehicle has set for a period of time and can be difficult to duplicate. The condition may occur after the vehicle has set for as little as 10 minutes or as long as overnight. It is most prevalent intermittently during the first 15 minutes of operation.

Correction

Technicians are to replace the EV fan clutch with a new design part, P/N 15293048, on vehicles built before June 2005. Vehicles built in June 2005 may already have the updated EV fan clutch and it will not need to be replaced. For 2004 model year vehicles and older, update the Powertrain Control Module (PCM) with a software calibration that was developed to improve coolant temperature gauge readings. This new calibration will cause the PCM to command small amounts of additional fan engagement to better control engine coolant temperatures. Model year 2005 vehicles already have this calibration installed. Refer to Corporate Service Bulletin Number 04-06-02-005 for more information about this calibration.

Proper diagnosis of any customer concern is essential. Refer to the Diagnostic Starting Point-Heating, Ventilation and Air Conditioning procedure in SI to begin a diagnosis of any HVAC concerns. Refer to the Diagnostic Starting Point-Engine Cooling procedure in SI to begin a diagnosis of any engine cooling or engine cooling fan concerns. If an attempt is made to diagnose an HVAC system concern, all parameters must be measured. As an example, both the low and high side refrigerant pressure readings must be measured. If only the low side pressure readings were measured, it would appear that the A/C compressor is disengaging at a higher pressure than expected. If both the low and high side pressures were being measured, it would be noted that the A/C compressor is probably disengaging due to the maximum high side pressure cut out point being reached. This occurs to protect the HVAC system from damage. The updated PCM software calibration along with the updated EV fan clutch will improve this condition due to increased air flow across the condenser. The new EV fan clutch has an increased minimum operating fan speed and an improved response time. Additional engine cooling fan noise can be expected with the updated PCM software calibrations.

The last area of customer concern is the operation of the HVAC system blower motor. For vehicles equipped with automatic control HVAC systems (RPO CJ2), the blower motor fan speed will be limited to 80% of maximum when the HVAC system is operating in the automatic mode. To obtain maximum blower motor speed, instruct the customer to manually adjust the blower motor speed to the highest setting.