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Old 7th June 2022, 09:26   #1
Soca
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Default strange noise from air con

I have a 2.5 v6 Connoisseur 2002.
The air con stopped working as there was a leak from a hose from the air con pump. I had it repaired at a local garage and they also had to replace the condenser as it had almost disintegrated. Since then I noticed a strange 'clattering' noise coming from the engine bay, only occurring on start up if the air con is switched on. If you press the economy switch, the clattering sound immediately stops. If you engage the aircon while driving, it works perfectly, with no clattering noise! I would value any ideas as to what's wrong with the air con, before returning it to the garage for further investigation, if I know what needs to be replaced I can get the part as I always like to supply my garage with the parts, much cheaper that way.

Another problem I noticed is that the coolant fan (radiator fan) does not engage at 99 degrees rather the temperature goes up to 115 before the high speed fan engages. If the air con is on the fan seems to work normally. Otherwise running the car, the temperature hovers around 90 degrees.
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Old 7th June 2022, 09:55   #2
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Quote:
Originally Posted by Soca View Post
I have a 2.5 v6 Connoisseur 2002.
The air con stopped working as there was a leak from a hose from the air con pump. I had it repaired at a local garage and they also had to replace the condenser as it had almost disintegrated. Since then I noticed a strange 'clattering' noise coming from the engine bay, only occurring on start up if the air con is switched on. If you press the economy switch, the clattering sound immediately stops. If you engage the aircon while driving, it works perfectly, with no clattering noise! I would value any ideas as to what's wrong with the air con, before returning it to the garage for further investigation, if I know what needs to be replaced I can get the part as I always like to supply my garage with the parts, much cheaper that way.

Quote:
Another problem I noticed is that the coolant fan (radiator fan) does not engage at 99 degrees rather the temperature goes up to 115 before the high speed fan engages. If the air con is on the fan seems to work normally. Otherwise running the car, the temperature hovers around 90 degrees.
Hi Nigel.
Start the car make sure the air con off, the press the demist button only, go round to the front of the car and see if the cooling fan is running continually, if no fan is running then the low speed on your fan as failed, look for a silver resistor if you have one it needs changing.

If you cannot see a silver resistor then you have a four wire three speed fan and the brushes most likely need changing.

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Last edited by Arctic; 7th June 2022 at 09:59..
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Old 7th June 2022, 10:47   #3
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Yes, have checked the low speed fan, seems to work perfectly! It’s just that the temperature gauge reads 99 degrees and the high speed fan doesn’t come on, but will come on when the temperature is much higher. I noticed in the Haynes manual they recommend fitting a new fan if the old one has been removed and I did ask the garage to give take the radiator out and give it a good flush, when they repaired the leaky air con. I am not sure if the removed the fan in the process.

There’s no silver resistor, so I guess the fan needs replacing or the brushes. Do you have to remove the fan to get to the brushes, or can I replace the fan with a new 2 speed fan?

Last edited by Soca; 7th June 2022 at 10:55.. Reason: Added more information
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Old 7th June 2022, 13:06   #4
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Yes, have checked the low speed fan, seems to work perfectly! It’s just that the temperature gauge reads 99 degrees and the high speed fan doesn’t come on, but will come on when the temperature is much higher. I noticed in the Haynes manual they recommend fitting a new fan if the old one has been removed and I did ask the garage to give take the radiator out and give it a good flush, when they repaired the leaky air con. I am not sure if the removed the fan in the process.

There’s no silver resistor, so I guess the fan needs replacing or the brushes. Do you have to remove the fan to get to the brushes, or can I replace the fan with a new 2 speed fan?
Hi Nigel
The low speed on a 2.5 petrol V6 should not come into force until the temp hits 101c yet you say the low speed is working, the fan does not need replacing just because it might have been removed from the car.

Yes you have to remove the front bumper, slam panel, de-gas the car or do the work round on the cowling so as not to disturb the gas.

You can fit a two wire 2 speed fan with gold resistor it would be plug and play.

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Do not take in all the Haynes manual says it's only any good for guidance, could you do a video and post it up with the true temp on the TPK 19 then 7 let the car run until the cooling fan kicks in so we can see what temp it's getting to.
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Old 7th June 2022, 13:30   #5
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I do have a spare 2 speed fan as I have been collecting spares for my rover for a while, along with a spare air con compressor. So I might just change the fan.

Any ideas on the clattering noise coming from the air con on start up? I’ve never heard anything like it before, the sound is something like you get when a fan fouls on something. I wondered if the clutch plate/bearing on the air con pump has worn and now the system has been re-gassed it has more work to do. It’s strange that it doesn’t do it every time, and is not there if you switch the air con on while going along.
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Old 8th June 2022, 07:17   #6
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... I did ask the garage to give take the radiator out and give it a good flush ...
Hello Nigel,

I suspect that your cooling system problems are related to this. The garage hasn't refilled and bled the system properly and you have an air lock.

First and most importantly, as Arctic has said, if your fan runs continuously with the windscreen demist button pressed then the fan does not need replacing. Don't waste your time and money on speculative purchases.
  • First thing in the morning with the engine cold, check the coolant level in the expansion tank. Is it near the bottom and looking into the tank through the filler neck can you see a tab marked 'MAX'?

Regarding the rattle heard only when you start the engine in 'Auto' mode but not when it's already running, this is a difficult one but it could be a cracked ancillary drive belt or its tensioner.

Club member Trikey is only down the road from you and I'm sure he'd be only too pleased to give you his diagnosis.

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Old 8th June 2022, 16:43   #7
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Are the fan blades loose on the motor spindle ?
This does happen !
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Old 8th June 2022, 17:24   #8
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Thank you for the help. Just went for a drive today, with the air con on the temperature was around 90 to 93 degrees for most of the journey, the temperature would climb to to 100 when stationary but would quickly drop to around 90 when moving again. So I don’t think I have air trapped in the coolant as air in the system usually has the effect of widely fluctuating temperatures as the air circulates around the system. Checking the water level when cold, the level has remained at maximum every time I have checked, so nothing leaking. With the air con off, the fan doesn’t seem to come on until the temperature goes up to above 105 by then my digital temperature gauge that I wired into the Canbus, is beeping a warning alarm! It’s weird that the fan seems to work normally when the air con is on but doesn’t seem to work properly if it is off.

At the moment I have to switch the air con on when going along, if I forget and start the engine with it on I get that strange clattering sound which goes away as soon as I turn off the air con or press the econ button. I am planning to have all the belts changed this year as its been 10 years (the car was garaged for two years) the car’s done about 40,000 miles since they were last changed. So might be able to sort the fan and econ noise when everything’s apart!
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Old 9th June 2022, 06:56   #9
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... the fan doesn’t seem to come on until the temperature goes up to above 105 by then my digital temperature gauge that I wired into the Canbus ...
Hi Nigel,

Thanks for the helpful temperature information, particularly the above. In your shoes I would disconnect your digital gauge from the CAN bus and use the car's built-in instrument pack diagnostics to confirm at what temperature the low speed fan is being triggered. Although your figures are good, I have a suspicion that your own digital gauge may be over-reading and I'm also concerned at tapping into the bus which controls engine function.

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Old 10th June 2022, 08:32   #10
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The digital temperature gauge has been fitted for 8 years now and has never been a problem, it was designed for the rover 75/mg zt. It’s easier to keep an eye on how the engine is performing than relying on the rover one.
The display sits in the middle of the row of switches underneath the heater controls, I would show you a photo of it but cannot seem to insert photographs from my iPhone!

I managed to speak to a mechanic who has years of experience with working on Rover75’s and MG ZT’s and he said the noise on start up was the air con pump failing as he had come across it before and also the problem with the fan would be due to the brushes failing. So planning to replace these next week and hopefully this will remedy the problems.
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