The clutch on the ac compressor free spins when it's not engaged.

It's electrically activates so when the computer sees the right conditions, it will engage and turn the pump.

If it never engages then it may be low system pressure (ie: leaking at the compressor or at a joint somewhere) or the compressor clutch may have gone bad electrically. Most shops will want to just change the compressor if the clutch goes bad. New compressor comes with a new clutch.

 

On the first gen Mini (and it may be similar on yours) the AC compressor clutch has coil in it that can fail. The coil can be replaced. The system does not need to be degassed to change the clutch coil.

If you only have one electrical wire going to the AC compressor then first measure the resistance to ground. Mine is around 200 Ohms. If it's short circuit or open circuit then you have a coil problem.

Alternatively unplug the coil and apply 12V (just for a moment) to the compressor, you should hear the compressor clutch click on and off. It will be a pretty clear if it is working.

You can also check 12V to the AC compressor - see if 12V reaches the compressor connector when you switch the AC on. Like you say it could be a relay or fuse.

However if the gas pressure is too low the AC compressor will not engage to protect it from damage - in that case 12V will never be sent to the compressor.

 

I've got another car battery , if I'm very briefly touching the coil connectors with a wire from the battery and there's 2 wires on the coil green and red do I need to touch one with positive and one with negative or does the chassis ground it ? , also from what I see it's not to difficult to change the coil through the wheel arch , lots of YouTube videos are talking about taking half of the car off ! , The concern I've got is getting the belt back on , always tricky!

 

I'll see if I can find out how to do it on your car, on mine it's simple, just the one wire.

 

Sorry, I can't find the wiring information for your car. Don't apply 12V until you know where to apply though - you could blow something!!! You could check the resistance between red and green, then green and chassis, then red and chassis.

 

Thanks , I'll have a look , the reason this all started is that I took car into be regassed and after waiting in the waiting room for about 2 minutes they guy said there was something wrong with the compressor and therefore he wouldn't waste my time regassing . Now I'm not sure about this after further investigation because after 2 minutes what checks could he have done? , if he's only going on the compressor not turning I've learnt since that it probably doesn't turn to avoid damage if the gas is low anyway, has anyone had any experience of this , not sure him looking at it for 2 minutes could have told him anything .

 

I don't know if it's the same in the UK, but a shop is legally not allowed to charge a system with a fault in this country. They can be subject to loss of license to work on air con and some pretty hefty fines if they're found to be outside the laws on it. Its an environmental thing.

2 mins is more than enough time to put the gauges on it and assess the charge. Air con is a sealed system and doesn't leak down unless there's a fault. Can be something as simple as the carbon seal on the compressor shaft has a little too much wear and is allowing refrigerant to bypass it.

Now the compressor clutch not working and condemning it simply because it's not engaging with a potentially low charge system? that
s a little bit of a "leap".

There might have been more going on than they told you though. Shops normally don't describe the troubleshooting process to the customer. That's time and time i money. they tell you what needs to be fixed and get on with it or push it out if you say no. It's a business after all....time is money.

 

The AC clutch won't engage if there isn't enough pressure.

In the UK virtually everyone uses an automatic machine that first evacuates any gas present, then runs a vacuum test, then fills the gas (and injects a small volume of oil).

The vacuum test takes something like 20 mins on its own.

I guess they could have connected the machine, read the manual gauges on the machine, seen there was good pressure on both the high pressure and low pressure sides, then checked operation of the clutch. You could do that in under 5 mins...but no one does that! Garages just hook up the machine let it run and come back when it's done. It won't fill if the vacuum test fails. If it does fill, then they double check the compressor kicks in and the temperature at the vents is cold.

But maybe, if the operator was particularly astute, then when they connected the machine they could have observed very good pressure readings and thought to check the AC clutch.

You could go somewhere else and ask for a regas. You could warn them and they could do the manual pressure check and if good check the AC clutch before gassing. It won't take long.

Using diagnostics you may be able to manually activate the AC clutch. On my older Mini you can trace the wire back to the relay and apply 12V there. You can see and hear the clutch activate. Using diagnostics you may be able to see if the car is seeing enough pressure on the AC system too.

 

get a second opinion from a different shop.