Chart C-12C Cooling Fan Check (No Low Speed Fan)

Chart C-12C, Cooling Fan Check - No Low Speed Fan:

A/C Head Pressure Switch Circuit:

*** This information has been updated according to Technical Service Bulletin #416507, dated April 1994.

CIRCUIT DESCRIPTION
Power for the fan motors comes from a 40A maxifuse element to terminal "30" on the relays. The relays are energized when current flows to ground through the PCM Quad-Driver #4. The left fan has two speeds and the right fan is a single speed fan.

Low Speed (Fan 1) Relay - The PCM energizes the relay through terminal "WD11" when engine coolant temperature reaches 100°C (212°F) or when A/C is requested.

High Speed (Fan 2) Relay - The high speed relay is energized by the PCM if the A/C head pressure switch opens, indicating refrigerant pressure above 210 psi (1448 kPa), or engine coolant temperature reaches 108°C (226°F).

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for B+ at relay harness connector.
2. Jumpering terminals "87" to "30" bypasses the relay, which should cause the fans to run if fan motors and wiring are OK.
3. Selecting Fan 1 with Tech 1 misc. tests and turning fans "ON" should cause the PCM to ground CKT 335. At this point, the test light should light, if the PCM is functioning and CKT 335 isn't open.
4. This checks for B+ and ground to the fan motor. A test light "ON" at this point indicates a faulty fan motor connection or motor.