Initial Inspection and Diagnostic Overview

GENERAL DIAGNOSTIC INFORMATION

COOLING FAN LOGIC
There are two cooling fans - a pusher and a puller. The fans run together at three different voltage levels to create three speeds or stages.
- Low speed - both fans in series - 6 volts each.
- Medium speed - both fans in parallel with resistor in series - 9 volts each.
- High speed - both fans in parallel without resistor -12 volts each.
The fan speed selected is based on coolant temperature or A/C system high side pressure.

Low Speed
- Enabled if coolant temperature exceeds 96 degrees C (204 degrees F) or A/C system pressure exceeds 1199 kPa (174 psi) high side.
- Disabled if coolant temperature goes below 92 degrees C (198 degrees F) and A/C system pressure goes below 799 kPa (116 psi) high side.

Medium Speed
- Enabled if coolant temperature exceeds 99 degrees C (210 degrees F) or A/C system pressure exceeds 1695 kPa (246 psi) high side.
- Back to Low speed if coolant temperature goes below 97 degrees C (207 degrees F) and A/C system pressure goes below 1399 kPa (203 psi) high side.

High Speed
- Enabled if coolant temperature exceeds 102 degrees C (216 degrees F) or A/C system pressure exceeds 2398 kPa (348 psi) high side.
- Back to Medium speed if coolant temperature goes below 100 degrees C (212 degrees F) and A/C system pressure goes below 2198 kPa (319 psi) high side.