A/C Compressor

AC Compressor:

Cars without TCS:
On activation of A/C, a 12 V signal is applied to pin 59 of the ECM. The ECM then shorts pin 54 to ground, the A/C relay operates and battery positive voltage (+30) is connected to the compressor and fan.

Engine speed compensation is incorporated in the ECM.

AC Compressor:

Cars with TCS:
On activation of A/C, a 12 V signal is applied to pin 37 of the ETS control module. This control module then shorts pin 38 to ground, the A/C relay operates and battery positive voltage (+30) is connected to the compressor and fan.

Engine speed compensation is incorporated in the ETS control module.

To ensure that engine speed compensation is as smooth and unobtrusive as possible, a signal is applied to pin 59 of the ECM unit which causes it to add a little extra fuel.