Description
System consists of an A/C control head, A/C refrigerant high and low pressure switches, A/C high and low temperature sensors, a control relay, compressor clutch and PCM.
When A/C control head is placed in A/C mode, request signal is sent to PCM. PCM will then energize A/C clutch relay, unless abnormally high or low A/C pressure is detected by A/C refrigerant pressure switches. PCM also monitors A/C low temperature sensors to cycle A/C clutch on and off. If PCM detects an A/C evaporator temperature less than 36°F (2°C), A/C clutch will be prohibited from being enabled. PCM will also energize cooling fans on when A/C is requested.
When PCM commands low speed fan operation it grounds cooling fan relay No. 1 which allows current to flow through both cooling fans in a series circuit to ground. If PCM commands high speed fan operation it grounds all cooling fan relays (including fan relay No. 1) which changes circuit to a parallel circuit to ground. If a fault occurs certain symptoms will occur due to series/parallel circuit design.
To determine if a fault is present perform COOLING FAN FUNCTIONAL CHECK. If DTC P1660 is present, or sets during functional check, it must be diagnosed before proceeding with any of the symptom checks.
PCM will command fan during low speed operation when engine coolant temperature exceeds 229°F (109°C), transmission fluid temperature exceeds 302°F (150°C), A/C operation is requested, if coolant temperature at key-off is more than 304°F (151°C), and system voltage was more than 12 volts, fans will stay on for about 3 minutes.
PCM will command fan during high speed operation when engine coolant temperature is less than 216°F (102°C), coolant temperature reaches 234°F (112°C), transmission fluid temperature is greater than 304°F (151°C), or when certain DTCs present. Fans will switch from high to low (except when DTCs set) when coolant drops to less than 229°F (109°C).
Note. Cooling fan No. 1 is left cooling fan. Cooling fan No. 2 is right cooling fan.
See also:
• K - SENSOR RANGE CHARTS