System descriptions

Fig 1: Identifying EMS Signal Input And Output

Courtesy of VOLVO CARS OF NORTH AMERICA.

Fan control

The engine's cooling fan control (FC) has two speeds, both controlled by Engine control module (ECM). Cars with AC are also equipped with a condenser fan, also controlled by Engine control module (ECM).

Control is determined by the following input signals:

engine's coolant temperature
car's speed
AC pressure
AC request from AC switch or automatic by ECC control module.

Condenser fan control

Control is determined by the following input signals:

car's speed
AC pressure

AC compressor control

Control is determined by the following input signals:

AC request from AC switch or automatic by ECC control module
engine's coolant temperature
AC pressure

The engine's load value is calculated using the mass air flow (MAF) sensor and RPM signal.

If the engine temperature sensor stops working, the condenser fan and cooling fan (FC) are run at speed 1. After start the engine's cooling fan (FC) will run for 2.5 min. with speed 1.

If the mass air flow (MAF) sensor stops working (no calculation of load), the cooling fan (FC) will run 10 min. after the ignition has been turned off.

The Limp-home value for a defective AC pressure sensor is 0 kPa. This means that the AC system will not operate.

After three full throttle signals (WOT) within 2 minutes, the AC remains engaged.

Fan and AC control

The engine's cooling fan will start with first speed under the following conditions:

engine temperature increasing over 100 °C (212 °F) and car speed lower than 115 km/h (71,5 mph).
pressure in AC system increasing above 1600 kPa (218 psi) and car speed lower than 115 km/h (71.5 mph).
if engine temperature increases over 115 °C (239 °F) when the ignition has been turned off, the engagement time is 2.5 min.
if engine temperature increases over 105 °C (221 °F) when the ignition has been turned off and the engine's calculated load level is higher than the limit value, the engagement time is 10 min.

The fan will start with second speed under the following conditions:

Engine temperature increasing over 115 °C (239 °F) and car speed higher than 115 km/h (71.5 mph) and fan has already been engaged for 5 seconds with speed 1.
Pressure in the AC system increasing over 2400 kPa (348 psi) and car speed is lower than 10 km/h and fan has already been engaged for 5 seconds with speed 1.

The condenser fan starts under the following conditions:

If engine temperature increases over 110 °C (230 °F) and car speed is lower than 90 km/h (56 mph).
If pressure in AC system increases above 1000 kPa (145 psi) and car speed is lower than 90 km/h (56 mph).

The AC compressor will be turned off under the following conditions.

engine temperature increases over 125 °C (257 °F)
pressure in AC system drops below 200 kPa (29 psi) or increases above 3000 kPa (435 psi).
at full throttle (WOT) for 10 seconds.