A/C Compressor Control Test

Start engine and allow to idle. Set air control knob in OFF position. For proper test results, temperature outside of vehicle must be 60°F (16°C) or more.
With A/C-heater control panel connected, measure voltage between Yellow wire of A/C-heater control panel connector and ground. If battery voltage exists, go to next step. If battery voltage does not exist, check Yellow wire for open circuit. If wire is okay, go to A/C CONTROL RELAY TEST.
Measure voltage between Black/White wire of A/C-heater control panel connector and ground. No voltage should exist. If battery voltage exists, check Black/White wire for short circuit to voltage. If Black/White wire is okay, replace A/C-heater control panel.
Turn ignition off. Set air control knob in OFF position. Disconnect A/C-heater control panel. Using a DVOM, measure resistance between Yellow and Black/White wires of A/C-heater control panel connector. Resistance should be infinite. If resistance is not infinite, replace A/C-heater control panel.
Set air control knob, in succession, to following positions: MAXIMUM, NORMAL, BI-LEVEL and DEFROST. Using a DVOM, measure resistance between Yellow and Black/White wires of A/C-heater control panel connector at each position. Resistance should be zero ohm. If resistance is zero ohm, go to next step. If resistance is not zero ohm, replace A/C-heater control panel.
Disconnect A/C low pressure cut-out switch. Connect a fused jumper wire between switch terminals on harness side. Measure voltage between Brown wire of A/C compressor relay and ground. If battery voltage does not exist, go to next step. If battery voltage exists, check A/C system refrigerant charge. If A/C system refrigerant charge is okay, replace low pressure cut-out switch.
Disconnect A/C high pressure cut-out switch. Connect a fused jumper wire between switch terminals on harness side. Measure voltage between Brown wire of A/C compressor relay and ground. If battery voltage exists, replace high pressure cut-out switch. If battery voltage does not exist, check Brown wire for open or short circuit.