02-05 Buick Rendezvous - Pontiac Aztek Evaporator Core Rattle or Chatter While Braking - kw brake chatter HVAC noise R134a

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Rattling or chattering type noise coming from the evaporator core area. The noise is present when the evaporator core is cold and system has run for sometime with the blower speed on between 3 to 5 (high). The noise is most prevalent on braking to a stop, however can be heard to some degree on a moderate acceleration from a stop. Cases have been reported where it can be heard with the nose of the vehicle pointed downward, setting still (a steep grade).

Cause: Evaporator core becomes loose and allowed to move around. The main noise is where the plastic bracing acts as a webbing supporting the upper and lower case contacts the evaporator core near the center. Contact points (witness marks) can be seen on the brace and core fins when the HVAC case module is taken apart.

To ensure the Evaporator core is the cause, remove the blower fan and shim between the evaporator core and HVAC case. Reinstall the blower fan and test the system. If the noise is gone follow the below listed steps. Remove the HVAC module case per SI. Split the case halves and shim the sides of core with thicker foam. Replace the system water channel tray at the bottom of lower case. Installed a piece of butyl tape on the bottom of case to act as a shim and also to hold the new tray in position. On the leading edge of the tray run a bead of RTV to keep the tray from vibrating due to air flow (may be overkill). Install a piece of one sided sticky foam between core and case support bracing. Use caution when installing upper case half to make sure this piece retains it proper position.

Installed a strip of butyl tape on the top of evaporator core to act as a shim, to ensure a tight fit. It is imperative that all procedures are done correctly. Any mistake could mean a lot of time to go back inside the case to repair. Follow SI to reinstall HVAC module. Note: Pay particular attention to the routing of the main dash wiring harness on disassembly as if you do not reinstall it the exact same way (snakes around crossbeam) means the crossbeam will have to come out again to reroute harness.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

(2002-05 Buick Rendezvous ) and (2002-05 Pontiac Aztek)

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