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Air-con noise and various

This is a free T4 Operator / owner finding service offered to all owners of 75 / ZT cars.
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Air-con noise and various

Post Number:#1  Post by scandalpete » February 28th, 2017, 11:52

Hi - great club - I've just subscribed having donated in the past. I have an '02 190 ZT-T with less than 58k on the clock and the only thing wrong is the noise from the air-con, which however works well. The noise sounds like bearings and is in direct correlation to engine speed - whichever gear I'm in. One MG garage in Havant, Hants, says its normal and another near Brighton said it was the air-con fan - but fans don't normally run in line with engine speed or do they ? Has anyone any idea ? Also any suggestions for a good servicing garage in the Portsmouth/Chichester area ? And what does T4 stand for ?
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Air-con noise and various

Post Number:#2  Post by Mr Hyde » February 28th, 2017, 2:39

Hi Pete

Thanks for the subscription! I've updated your profile :D
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Air-con noise and various

Post Number:#3  Post by KDA4G » February 28th, 2017, 5:44

A couple of things...
- There is no air-con fan, as such.
- The heater fan, and the radiator fan, have a variety of fixed speeds, but no, they don't go up and down with the engine revs.
- The air-con compressor is driven off the engine, though. Does the noise happen with the air-con off (e.g. economy mode)?
- T4 is the dealer diagnostic system, which can read out any stored fault codes, but that doesn't sound relevant just yet.
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Air-con noise and various

Post Number:#4  Post by Duncan » February 28th, 2017, 8:00

If the fan is not working, it can cause the aircon system to be noisy when the engine is running. So first thing is to check the fan is working on all speeds (2 or 3). T4 has very little diagnostics for the aircon.
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Air-con noise and various

Post Number:#5  Post by scandalpete » February 28th, 2017, 10:08

Many thanks for replies.
The noise in question is not there when the air-con is off. The heater fan works at all speeds and makes a normal background noise consistent with the fan speed setting -independent of engine speed. Immediately the air-con is switched on at whatever setting this intrusive noise begins - enough to encourage me to keep if off. The radiator fan works when needed and is not the cause of the noise.
Thanks for the info about T4 - I thought it might refer to a dealer network.
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Air-con noise and various

Post Number:#6  Post by Duncan » March 1st, 2017, 9:35

scandalpete (view post) wrote:Many thanks for replies.
The noise in question is not there when the air-con is off. The heater fan works at all speeds and makes a normal background noise consistent with the fan speed setting -independent of engine speed. Immediately the air-con is switched on at whatever setting this intrusive noise begins - enough to encourage me to keep if off. The radiator fan works when needed and is not the cause of the noise.
Thanks for the info about T4 - I thought it might refer to a dealer network.


We aren't talking about the heater fan inside the car, but the cooling fan at the front of the car.

Just to explain: If the cooling fan isn't working it may not be the source of the noise, but could be the cause. When the cooling fan isn't running the refrigerant gas in the A/C system gets too hot and the pressure is too high. This has been known to cause a variety of strange noises and could vary with engine speed as the compressor is engine driven. Cooling fan failure is quite common, hence why it was suggested to check it as an easy first step. If its not working you need to fix it anyway as running without it stresses the A/C system.

Your problem could still lie elsewhere (compressor, crank pulley, refrigerant level) but its worth fully checking your cooling fan as a starting point. It has more than one speed and its almost always a part failure where it will still run at full speed but not at the lower speeds required for A/C.
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Air-con noise and various

Post Number:#7  Post by scandalpete » March 1st, 2017, 10:37

Thanks for that info. I used the term radiator fan rather than cooling fan i.e. the fan visible through the front grill. This does not come on when the car is started but does so when the air-con is fired up. It also comes on for example at the end of a run while parking and after a coup,le of minutes turns itself off. I do not know how to check that it is working properly. You suggest this fan has more than one speed. Should it be working whatever the engine temperature e.g. immediately the engine is started ? Would an air-con specialist be the best port of call or an MG dealer ?
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Air-con noise and various

Post Number:#8  Post by KDA4G » March 2nd, 2017, 2:38

The radiator fan should run, either:
- whenever the air-con compressor is running, or
- whenever the engine temperature requires it, which is a bit complicated.

You have the ZT-T 190, so it's a 2.5 V6 engine. It will have either the early 3-speed radiator fan, or the later 2-speed radiator fan, and it's important that it works correctly. Typically, it would not run from a cold start, but would do the normal thing of cycling on and off in heavy traffic, and maybe continuing to run on for a few minutes, after switching off at the end of a long journey. It should always run when the air-con is active.

The suggestion would be to confirm this first, before looking at the air-con itself.
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Air-con noise and various

Post Number:#9  Post by Duncan » March 2nd, 2017, 6:51

An aircon specialist probably can't fully test it as they are unlikely to have something to force it to run. An MG specialist could if they have a T4 which is the diagnostic computer. That can force the fan to run at each speed it should. If you were closer to me I'd test it for you, but Stafford is a long way!
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Air-con noise and various

Post Number:#10  Post by scandalpete » March 3rd, 2017, 5:02

Thanks again for all this help.
In answer to KDA4G's comments it seems to me that these criteria are met although whether the fan runs at 2 (or more) speeds.
To Duncan I would say that I may well be prepared to come to Stafford but maybe should ask if there is a garage equally as capable (and interested in sorting out the problem) as her is nearer to me on the South Coast ?
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Air-con noise and various

Post Number:#11  Post by Duncan » March 3rd, 2017, 6:05

I expect there is someone much closer who could help. For example there's a guy known as T4Phil who is in Milton Keynes. Hopefully someone will come along and recommend someone even closer.
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Air-con noise and various

Post Number:#12  Post by scandalpete » March 3rd, 2017, 6:45

Thanks for that - Having looked at various comments on the forum I'm going to try Gregory's Garage (T4) in Fareham which has had good reviews and is not far from me. I'll report back.
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