Description - engine management (ENGINE MANAGEMENT SYSTEM - V8) (page 42 of 43)

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-47

ATC compressor clutch relay

The ATC compressor clutch relay is located in the engine compartment fuse box. It is a four pin normally open relay. 
The relay must be energised to drive the ATC compressor clutch.

Input/Output
The ECM provides the earth for the relay coil to allow the relay contacts to close and the ATC clutch drive to receive 
battery voltage. The ECM uses a transistor as a switch to generate an open circuit in the earth path of the relay coil.  
When the ECM opens the earth path, the return spring in the relay will pull the contacts apart to shut down the ATC 
clutch drive.

Input to the ATC clutch relay switching contacts is via fuse 6 located in the engine compartment fuse box. The relay 
coils are supplied with battery voltage from the main relay, also located in the engine compartment fuse box. The earth 
path for the relay coil is via pin 29 of the ECM C0657 connector. When the relay is energised the output from the 
switching contacts goes directly to the ATC compressor clutch.

The ATC clutch relay can fail in the following ways:

l

Relay open circuit.

l

Short circuit to vehicle supply.

l

Short circuit to vehicle earth.

l

Broken return spring.

In the event of an ATC clutch relay failure, the ATC does not work.

Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by 
TestBook.

P Code

J2012 Description

Land Rover Description

P1536

Air conditioning compressor request range/
performance

ATC compressor clutch relay open circuit

P1537

Air conditioning compressor request low input

ATC compressor clutch relay short to earth

P1538

Air conditioning compressor request high input

ATC compressor clutch relay short to battery supply