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Old 16-04-2011, 09:22   #1
holland.666
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Exclamation Rover 75 coolant sensor

Hi!
Been reading the forum regarding coolant temp and coolant fan.
Is it right that if the coolant sensor is sending incorrect information to the ECU then the fan won't kick in.
Only the reason i'm posting this is that i started the car from cold plugged the diagnostic machine in to read the temp and took coolant temp to 104-108 celsius (reading from diagnostic machine) but the fan did not come on.
Checked the fan was working via the air con and runs at high speed after 10 seconds after the air con is switched on.
But the temp on the dash is reading middle on the gauge. Need to get the coolant fan working and wondered what sensor i need to check>

thanks
paul
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Old 16-04-2011, 10:10   #2
T-Cut
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I'd say the slow speed in the fan motor has failed. The coolant sensor is probably OK from your readings. If the slow speed fails, the high speed will be tripped when the systems get to emergency state. For engine cooling, that's around 112C in the 1.8. The aircon system also needs slow speed cooling, but without that, the system overheats (due to lack of condensing function) and trips emergency cooling (high speed). This will cycle on and off every 30 seconds or so as the system overheats, then cools.

Since your car is a 2002 registration, it's probably got the original brush-controlled motor. The slow speed brushes have worn away. IF it has the later resistor-controlled motor, then the resistor has blown. Check behind the fan blades in the 2 o'clock position for the thin aluminium resistor unit. If itt's there, you're in luck (cheap fix). If not, you need a new motor.

The temperature gauge on the dash reads 'normal' across the range 75-115C. So not very useful.

TC
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Old 16-04-2011, 10:27   #3
holland.666
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Thanks for that
So if the is not running constantly running at slow speed when the air con is on, then as you say the fault lies in the fan. Is it the same fan that runs the engine coolant the same fan for the air con.

paul
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Old 16-04-2011, 10:45   #4
holland.666
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Just to update when the air con is switched on the fan will run constantly at high speed and not intermittently.
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Old 16-04-2011, 14:28   #5
Mike Noc
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Quote:
Originally Posted by holland.666 View Post
Thanks for that
So if the is not running constantly running at slow speed when the air con is on, then as you say the fault lies in the fan. Is it the same fan that runs the engine coolant the same fan for the air con.

paul
Paul yes there is only one fan and as TC said sounds like it has failed on the slow speed. If you can see a silver resistor then it is worth replacing it with the gold coloured uprated type.


Mike
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Old 16-04-2011, 16:35   #6
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Originally Posted by holland.666 View Post
Just to update when the air con is switched on the fan will run constantly at high speed and not intermittently.
If that's so, then there must be two issues. The aircon and normal engine cooling require the slow speed fan. The high speed is ONLY used for emergency cooling of the aircon and after hot engine shut down (heat soak condition). If aircon invokes continuous high speed than the trinary valve is stuck in the high pressure mode. If the trinary is functioning correctly, it will trip high speed in 30 second pulses as the system cools then reheats. The same trinary condition will appear if the aircon condenser has lost efficiency so the fan is ineffective. The condenser is succeptible to weathering being at the sharp end of the car and the fins can disintegrate.

TC
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Old 17-04-2011, 10:41   #7
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Exclamation rover 75 coolant fan

Hi!
Can any body tell me if it is possible to change the brushes on the old type motor the one without the resister, and where to get them.

thanks

paul
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Old 17-04-2011, 11:16   #8
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Changing the brushes has been done but the chances of the motor being in a recoverable state are about 50/50. Often the commutator is damaged. You should check the condenser matrix before stripping down the motor.

TC
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Old 17-04-2011, 12:42   #9
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Thanks!
Can you tell me where the condenser matrix is.
One other thing if i need to change the fan can i get the one with the resister and plug it in without rewiring.

thanks

paul
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Old 17-04-2011, 12:58   #10
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Originally Posted by holland.666 View Post
Just to update when the air con is switched on the fan will run constantly at high speed and not intermittently.
Hi, Are you sure it's high speed? When I got my car the resistor had blown so no fan when the aircon was on. I replaced the resistor with the gold one and it surprised me how fast the fan goes. It's described as slow speed but looks quite fast. Obviously not as fast as full speed but I wouldn't describe it as slow. Just a thought.

Regards, John
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Old 17-04-2011, 14:06   #11
holland.666
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As it goes if you take the climate controle down to low the coolant fan will kick in, if you take the climate controle up to 20 then the fan will kick in and out while the car is stationary, don't know if it the same whist driving.

regards, paul
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Old 17-04-2011, 14:42   #12
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Originally Posted by holland.666 View Post
As it goes if you take the climate controle down to low the coolant fan will kick in, if you take the climate controle up to 20 then the fan will kick in and out while the car is stationary, don't know if it the same whist driving.

regards, paul
Hi, that sounds normal. When my resistor failed and had the climate control on low the fan did not spin at first. After about 2 minutes the fan would come on flat out for about 30 seconds then go off. This would keep doing this until the aircon was turned off. Now fixed when the aircon is on the fan starts immediately but at a slower speed. Definitely slower than flat out but still looks quite fast.

Regards, John
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Old 17-04-2011, 17:58   #13
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Originally Posted by holland.666 View Post
As it goes if you take the climate controle down to low the coolant fan will kick in, if you take the climate controle up to 20 then the fan will kick in and out while the car is stationary, don't know if it the same whist driving.
Whenever the refrigeration system is running, the slow speed cooling fan must also run continuously. Obviously, whether the refrigeration system runs depends on what temperature you set the interior. If this is set below ambient, then the system has to run to cool the air to below ambient. If you set the temperature above ambient, the only the heating system will be used. If you set the temperature a degree or so below ambient, then the freezer system may run intermittantly as the interior temperature is trimmed to your setting. I've not read of the system doing this. I believe the fan runs whenever the aircon is in Auto mode. The fan may not run when ambient is so low that forced cooling for the condenser isn't needed. When the slow speed fan has failed, the aircon may appear fully functional while the car's running forward. The air flow from the ram effect suffices. When stationary, problems start.

If the fan's slow speed has failed (whether it's a 2 or a 3-speed motor), then normal condenser cooling isn't immediately available So, the aircon gas overheats, raising the internal pressure. The compressor exacerbates the problem. The high pressure trips the trinary valve to invoke high speed emergency cooling. This runs for about 30 seconds, sufficient to reduce the temperature/pressure, so then trinary stops the fan. This cycle will obviously repeat and so you get high speed cycling. This is different from a slow speed cycle that may happen when the interior setting is just below ambient with an otherwise functional fan (though I don't think it actually does so).

TC

Last edited by T-Cut; 17-04-2011 at 18:05.
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Old 17-04-2011, 18:21   #14
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Originally Posted by holland.666 View Post
Can you tell me where the condenser matrix is.
It's mounted on the front of the main radiator. You need the front bumper off to check the fins. These often disintegrate into a pile of dust. When that happens, the aircon system can go into melt down if the slow speed fan has failed. Even the high speed fan may not cool the gas enough. I think the system may actually shut down before the bottom drops out.

Quote:
if i need to change the fan can i get the one with the resister and plug it in without rewiring.
New 2-speed fans are basically plug'n'play with existing wiring. A second hand one may require minor wiring adjustment. It's all on record somewhere.

TC

Last edited by T-Cut; 17-04-2011 at 19:38.
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