1971 Corvette: Service Bulletin: Anti-Diesel Relay

Subject:   Anti-Diesel Relay
Model and Year:   (1971) All Passenger Cars and Light Trucks with Air Conditioning Except Vega
Source:  Chevrolet Dealer Service Technical Bulletin
Bulletin No:   71-T-44
Section:    Ia
Date:   Aug. 5, 1971

TO:  ALL CHEVROLET DEALERS

Delcotron feedback at the anti-diesel relay can result in a shorted transistor in the timing circuit of the relay.  A shorted transistor will cause the anti-diesel relay to hold the air conditioning compressor clutch engaged continuously, after the engine is turned off, draining the battery.

A new anti-diesel relay, with a suppression diode across the relay coil to protect the transistor, entered production the week of April 26, 1971, at all assembly plants.  Also, a blocking diode is being installed at the voltage regulator to prevent Delcotron feedback on all models except Corvette.  The Corvette uses the new relay but, due to the integrated regulator, does not require the voltage regulator blocking diode.

For service on light trucks, to prevent Delcotron feedback to the anti-diesel relay, blocking diode, Part Number 6273302, should be installed at the voltage regulator as outlined under Service Procedure - Truck.

On passenger cars, Delcotron feedback to the anti-diesel relay can be prevented by relocating the relay feed wire at the fuse block, from the ignition terminal to the accessory terminal.  Installing the blocking diode at the voltage regulator is not necessary.

These changes should be made on early production vehicles in for normal service or in dealer stock to avoid future possible customer inconvenience.

In instances where the anti-diesel relay is found to be shorted, the relay should be replaced with relay, Part Number 6273301, in addition to the above changes.

Chevrolet Motor Division
General Motors Corporation