A/C Signal: Description and Operation

A/C Clutch Control Circuit - 3.1L 92 U Body:

PURPOSE
Provides ECM control of the A/C clutch to improve idle quality and engine performance.

CONSTRUCTION
The ECM controlled A/C circuit system consists of:
- Heater and A/C control assembly located at the dashboard.
- Low pressure switch (Front A/C option).
- High pressure cut-out switch (Front and Rear A/C option).
- Control relay
- Compressor
- High pressure fan control switch

OPERATION
The low pressure switch, mounted in the compressor, is closed when the system contains a sufficient refrigerant charge and warm climate temperature exists. This switch opens when A/C pressure is less than about 40 psi (276 kPa).

The high pressure cut-out switch (normally closed) opens when pressure is greater than about 440 psi (3034 kPa). This disables the A/C clutch before damage can occur to the system.

The A/C control relay is controlled by the ECM. This allows the ECM to:
- Delay clutch engagement (about 8 seconds) until idle speed is increased.
- Release clutch when engine temperature exceeds 125~C (257~F).
- Release clutch during Wide Open Throttle (WOT).
- Prevent clutch engagement until engine RPM is below 4000 RPM for 3 seconds.

TCC engagement is also affected by A/C operation by:
- A/C "ON" engagement speed is approximately 35 mph.
- A/C "OFF" engagement speed is approximately 30 mph.

High pressure fan control switch will open, if the A/C pressure exceeds about 200 psi (1380 kPa)

The compressor is a variable displacement compressor called a V-5. The V-5 meets A/C requirements without cycling.