A/C Compressor Mode Control Test

Start engine and allow to idle. Turn air control knob to 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 ground and Red/Black/White wire (backprobe wire) of A/C-heater control panel connector. If battery voltage is present, go to next step. If battery voltage is not present, check Red/Black/White and Brown wires for open. Repair wiring as necessary.
Measure voltage between ground and Black/White wire (backprobe wire) of A/C-heater control panel connector. No voltage should be present. If no voltage is present, go to next step. If voltage is present, check Black/White wire for short to voltage. Repair wiring as necessary. If Black/White wire is okay, replace A/C-heater control panel.
Turn ignition off. Ensure air control knob is in off position. Disconnect A/C-heater control panel 3-pin connector. Using a DVOM, measure resistance between Red/Black/White and Black/White wires of A/C-heater control panel connector. Resistance should be infinite. If resistance is infinite, go to next step. If resistance is not infinite, replace A/C-heater control panel.
Set air control knob, in succession, to maximum, normal, bi-level and defrost. Using a DVOM, measure resistance between Red/Black/White and Black/White wires of A/C-heater control panel connector at each knob position. Resistance should be zero ohms. If resistance is zero ohms, go to next step. If resistance is not zero ohms, 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 ground and Blue wire (backprobe connector) of A/C compressor relay connector. If battery voltage is not present, go to next step. If battery voltage is present, 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 ground and Blue wire (backprobe connector) of A/C compressor relay connector. If battery voltage is present, replace high pressure cut-out switch. If battery voltage is not present, check Blue wire for open or short.