A/C - System Hissing Noise, Component Updates
File In Section: O1 - HVACBulletin No.: 99-01-39-006A
Date: August, 2000
INFORMATION
Subject:
Production Changes to A/C System Components, Revisions to Reduce
Possible Passenger Compartment Hiss Noise and New Charging Guidelines
Models:
1999 Chevrolet Corvette
This bulletin is being revised to clarify and add additional A/C system changes Please discard Corporate Bulletin Number 99-01-39-006 (01 - HVAC).
This information is intended to aid the technician by outlining the 1999 changes to the A/C system and the normal sounds associated with it. On April 12, 1999, several production changes were instituted to reduce a possible hiss type noise. Previous to this production date, a hissing sound may have been audible inside the passenger compartment while the A/C compressor was in operation. A hissing sound may be created when the high pressure R134a liquid refrigerant changes into a gas as it passes through the expansion tube. No attempt should be made to alter the previous system, as it is functioning correctly. The April 12, 1999 revisions to the system are as follows:
^ The expansion tube (or orifice) is relocated to the front refrigerant line, closer to the condenser.
^ The expansion tube goes from a 1.83 mm (.072 in) diameter to a 1.57 mm (.062 in) diameter.
^ The revised front and rear refrigerant lines can only be used as a pair. The new design and old design cannot be mixed.
Charging Guidelines
^ Vehicles built after April 12,1999 equipped with the revised refrigerant lines, were charged from the factory with 0.68kg (1.50 lbs) of R134a refrigerant. Near the end of the 1999 production, a running change was made to increase the refrigerant charge to 0.794 kg (1.75 lbs). The factory charge amount can be verified by checking the A/C system label affixed to the front passenger side wheelhouse.
^ For vehicles factory charged with 0.68 kg (1.50 lbs) of refrigerant, the charge may be increased to 0.794 kg (1.75 lbs) only if the system must be evacuated for repair purposes.
Important:
Do not increase the charge unless repairs to the system or other components necessitate evacuation of the system.
^ If a vehicle's reported customer concern is insufficient cooling, the system charge may be increased to 0.794 kg (1.75 lbs). All A/C system diagnostics in the Service Manual should be followed in conjunction with the refrigerant increase.
Parts are currently available from GMSPO.
^ Increasing the system charge should not be considered a "fix" for insufficient cooling, as it will have only a minimal affect on system performance. If the system charge is increased to 0.794 kg (1.75 lbs), the underhood charge label must be replaced with P/N 10432250.