Thermo fans operation

[codybailey]

Should both thermo fans switch on as soon as air con switched on ? Or only one, been told leftside only comes on if engine getting too hot ???

[heartzzonfire]

Usually both the fans come on as soon as you switch on the A/C.

I have noticed that the A/C thermo fan speed is slow compared to the Radiator Fan, wanted to know if this is normal on a VZ Commodore 05 ?

Thanks..

[slidways]

yeah both fans come on when the a/c is switched on

[Torquative]

hmm.......

Stage 1 Fan Operation

The large cooling fan operation is enabled with the ECM via circuit 335 energises the Engine Cooling Fan Relay 1 (R7). When the negative terminal is connected to ground through Engine Cooling Fan Relay 1 (R7), the large cooling fan (right) operates.

The ECM determines when to enable the Engine Cooling Fan Relay 1 (R7), based on inputs from the A/C request signal, Engine Coolant Temperature sensor (ECT) and Vehicle Speed Sensor (VSS)

Condititions for stage 1 cooling fan engagement

The ECM turns Engine Cooling Fan Relay 1 (R7) ON when:

* Air conditioning request indicated (YES) and the vehicle speed is less then 30kph
*Air conditioning pressure is greater then 1,500kPa
*Coolant temperature is greater then 104 C or
*an ECT sensor failure is detected by the ECM.

When the ignition switch is turned from ON to OFF and the engine coolant temperature is above 117C the ECM will continue to energise the Engine Cooling Fan Relay 1 (R7) for approximately four minutes.

The ECM turns Engine Cooling Fan Relay 1 (R7) OFF when the following conditions have been met;

*Air conditioning request not indicated (NO) and the coolant temperature is less then 99C or
*Air conditioning request indicated (YES) with pressure less than 1,700kPa, vehicle speed greater than 50kph and coolant temperature less then 99C

Stage 2 Fan Operation

The small (left) cooling fan operation is enabled when the ECM via circuit 473 energises the Engine Cooling Fan Relay 2 (R5). When the negative terminal is connected to earth via the Engine Cooling Fan Relay 2 (R5), the small cooling fan operates. Both cooling fans are now operational, the large fan via the Engine Cooling Fan Relay 1 (R7) and the small cooling fan via Engine Cooling Relay 2 (R5)

Conditions for Stage 2 Fan Operation

The ECM determines when to enable the Engine Cooling Fan Relay 2 (R5), based on inputs from the ECT sensor.

The ECM turns Engine Cooling Fan Relay 2 (R5) ON if the Engine Cooling Fan Relay 1 (R7) has been energised for one second and the following conditions have been met:

*if there is a ECM message response fault, setting a DTC (P1258)
*The ECM detects an ECT sensor failure
*Engine coolant temperature is above 108C, or
*Air conditioning pressure is greater than 2000kPa

Note - if the large engine cooling fan is off when the criteria for turning the small engine cooling fan on are first met, the small engine cooling fan will turn on 5 seconds after the large engine cooling fan is switched on.

If both the large and small cooling fans are enabled, the ECM turns the small engine cooling fan OFF via Engine Cooling Fan Relay 2 when,

*The engine coolant temperature is less than 103C,and
*Air conditioning request is not indicated (NO) OR
*Air conditioning request is indicated (YES) and the pressure is less than 1500kPa

So basically the small one shouldnt turn on unless you have an ECM fault, ECT failure, although more realistically it would be because your coolant temp is above 108C or the AC pressure is more then 2000Kpa. I have never seen mine running in the Acclaim, and have only ever heard it kick in once in the Adventra after towing a heavy load up a hill on a 40 degree day.

Hope this helps!

[codybailey]

Thanks for info always thought both came on when aircon on !!! Did on vt

[Little Red VZ Go-Kart]

When the techie was instructing me at delivery with the bonnet up and engine running with air-conditioning on, I did not see either of the two fans operating. Is the fan operation described in this thread consistent from one model to the next, or subject to revisions here and there?

[FnomnaVZ]

Was it a cold day? There may not have been enough pressure in the A/C to turn on stage 1 of fans (see above). I notice on mine if I have the A/C on on a cold day and stop, it takes a while until the fan turns on.