1978 Corvette: Service Bulletin: Air Conditioning Compressor Noise
Subject: Air Conditioning Compressor Noise
Model and Year: 1978 Corvette with RPO L48 Engine and M38 Automatic Transmission
Source: Chevrolet Dealer Service Technical Bulletin
Bulletin No: 78-T-76
Date: February 1979
TO: ALL CHEVROLET DEALERS
Some 1978 Corvettes with air conditioning may exhibit a rumbling type noise most noticeable at or just off idle RPM, with the air conditioning on, and the transmission in drive.
This condition usually occurs under high ambient temperatures and high head pressured and is caused by a reduction of compressor mounting bolt torque which results in compressor "wobble" and subsequent abnormal deflection of the compressor belt.
In production, the compressor mounting has been revised for 1979 Corvettes. Complaint vehicles can be corrected by using a new mounting bracket spacer, P/N 3976216, and the addition of a sleeve fabricated from a Corvette headlamp actuator sleeve, P/N 3922498, as outlined on page 2.
- Obtain P/N 3976216 spacer and P/N 3922498 sleeve from stock.
- Cut the P/N 3922498 plastic sleeve in half, resulting in two .250" long sleeves of which one will be used.
- Remove the compressor belt and disassemble the compressor from the mounting brackets.
- Lift compressor from bracket to allow access to both the original spacer in the mounting bracket hole and the mounting hole in the front face of the compressor where the feed-through bolt will exit.
- Remove original spacer and install new spacer, P/N 3976216 in its place and the fabricated sleeve (.250") in the compressor face mounting hole as shown in Figure 1.
- Reinstall compressor and belt.
- Finalize the repair by tightening the compressor belt to 100 +/- 5 lbs. and torquing the compressor mounting bolts to 30 ft. lbs.