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Engine Fans: Low works normal but high never comes on

3K views 11 replies 8 participants last post by  exigegus 
#1 ·
I have searched for something realatively close to this, but haven't had any luck. So, the car (2005 Lotus Elise, sport and touring pack, with a/c) I am looking at has some a/c issues which seem to be caused by engine fan opperation. From what I can tell there is 4 opperations for the dual engine fans.

1) Cold engine with a/c off, fans off
2) Cold engine with a/c on, fans operate on high
3) Hot engine with a/c off, fans operate on low
4) Hot engine with a/c on, fans operate on high

Below are how the car operates.

1) Cold engine with a/c off, fans off
2) Cold engine with a/c on, fans off
3) Hot engine with a/c off, fans operate on low
4) How engine with a/c on, fans operate on low

Since the fans never go to high, the a/c doesn't perform.

The owner says he took it to the dealer in Austin, TX and they told him one of the fans were bad. This doesn't sound right to me. I would think if one fan was bad, only one would act out of the norm, but both do. I am thinking wiring or maybe a module, but I don't have much experience with this. Thanks for your expert help.
 
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#2 ·
- RADIATOR FAN & RE-CIRC. PUMP CONTROL
The two cooling fans are fitted beneath the radiator or (with a.c.) condenser/radiator package, and the coolant re-circulation pump is mounted below the header tank. Both the fans and pump are controlled by the engine management ECU using data provided by the engine coolant temperature sensor mounted in the back of the cylinder head.
The cooling fans are switched as a pair, and will operate at half speed (connected in series) when coolant temperature reaches 208°f on rise, and switch off at 201°f on fall.
The fans will also operate at half speed irrespective of coolant temperature if the a.c. is switched on and the compressor is running.
If coolant temperature rises to 217°f, the fans will switch to full speed (connected in parallel), reverting to half speed at 208°f.
The fans will also run at half speed, unless high coolant temperature dictates otherwise, when the a.c. is switched on and the compressor is running, or if the engine management system detects a fault with the inlet air temperature or coolant temperature circuits.
At road speeds in excess of 85 mph (135 km/h), equating to the fan stall speed, all fan functions are switched off.

A trinary switch fitted into the top of the receiver-drier senses the pressure of refrigerant and allows
system operation only within a pressure range of 2 to 32 bar (29 – 464 psi) in order to prevent system damage from too high
a pressure, or from compressor oil starvation damage caused by too low a pressure. A third switching point is
used to engage the two condenser fans at half speed at pressures over 17.5 bar (see also sub-section KH.5).
An additional safeguard is provided in the form of a high pressure relief valve in the condenser inlet pipe, which
opens at 38 - 41 bar.

Michael
 
#5 ·
I had a fan go out on my exige, the symptoms are different than yours. The fan would only come on with the high speed mode (ac on or hot) because the fans are power in parallel effectively bypassing the bad fan in the circuit.

Aj
 
#12 ·
I didn't do anything, that is how it acts. I actually replaced the fan control module and it acts the same way, so it is not a mod. It does not appear to be the way the shop manual describes it

I would check the behavior of your system with a proper charge of 134 and a very hot day and see how it acts

Oh, and the trinary switch turns the ac compressor off for low pressure, off for too high pressure and turns the fans on at a certain pressure
 
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