1.8L PRIZM: Description

Engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. Relays are arranged in a series/parallel configuration that allows Powertrain Control Module (PCM) to operate both fans together at low or high speeds. Cooling fans and fan relays receive battery voltage on 2 individual power circuits, from fuse and relay block 1 and from junction block 2. During high speed operation, which is when ECT reaches 199°F (93°C) or A/C system pressure exceeds 220 psi, PCM removes ground for fan 1 and fan 2 relays through cooling fan relay control circuit. This de-energizes fan 2 relay which switches relay contacts and provides a ground path for auxiliary fan motor. At the same time, fan 1 relay is de-energized, closing relay contacts and providing battery voltage on main fan motor supply voltage circuit to main fan motor.

During low speed operation, which is when A/C is operating and Engine Coolant Temperature (ECT) is less than 181°F (83°C), PCM supplies ground path for fan 1 and fan 2 relays through cooling fan relay control circuit. This energizes both relays, opens fan 1 relay contacts and switches contacts in fan 2 relay. Engine main relay supplies battery voltage through cooling fan motor supply voltage circuit to auxiliary fan motor. When A/C is operating, compressor clutch (MG) relay energizes fan 3 relay. Ground path for auxiliary fan motor is through switched contacts in fan 2 relay, through closed contacts of fan 3 relay and through main fan motor to ground. Result is a series circuit with both fans running at low speed.

During high speed fan operation, both engine cooling fans have their own power and ground path. Result is a parallel circuit with both fans running at high speed. A/C high pressure switch is in series with PCM controlled ground for coils of fan 1 and fan 2 relays. If A/C system pressure exceeds 220 psi, pressure switch opens ground circuit to coils of fan 1 and 2 relays. This has same effect as if PCM had removed ground for relays. PCM will control ground for fan relays based on input from ECT sensor in order to maintain cooling system at normal operating temperature.

Main and auxiliary fan motors run at half speed in series configuration when all of the following conditions occur:

• A/C system is operating.
• A/C system pressure is less than 178 psi.
• ECT is less than 181°F (83°C).

Main and auxiliary fan motors run at full speed in parallel configuration when either of the following conditions occur:

• ECT reaches 199°F (93°C).
• A/C system pressure exceeds 220 psi.