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[Doctor Gollum]

Better to have it done properly than DIY with a refill/bodging kit for several reasons...

[Marks DTM Calib]

So, this where I struggle to understand....

If the aircon or climate is managing to frost the windscreen, it suggests to me the air coming from the vents must be below 0c 
A temp inside the vents of about 5c is norm I would have thought 
Also if climate why is it venting the air onto windscreen, unless you have it on manual and selected the windscreen vents....climate on my cars left on auto have always vented through the dash vents ....

As an example, sun on the screen means the climate directs additional air to the screen for cooling (thanks to the sun sensor).

No aircon setup will have the condenser temp at less than 4 deg C or it would freeze up, most are about 5-6.

[TD]

So, this where I struggle to understand....

If the aircon or climate is managing to frost the windscreen, it suggests to me the air coming from the vents must be below 0c 
A temp inside the vents of about 5c is norm I would have thought 
Also if climate why is it venting the air onto windscreen, unless you have it on manual and selected the windscreen vents....climate on my cars left on auto have always vented through the dash vents ....

As an example, sun on the screen means the climate directs additional air to the screen for cooling (thanks to the sun sensor).

No aircon setup will have the condenser temp at less than 4 deg C or it would freeze up, most are about 5-6.

Ok, I get the first bit.....but how can you get frost forming....with a air temp of 5-6C? 

The other thing I struggle to understand is the compressor .....

Compressor job is turn the gas back into liquid.....so cooling can take place as the liquid turns to gas.....correct?

So if the compressor is running at engine idling speed its compressing the gas back to liquid......but if the compressor is running at engine speed of 3k revs for example......does the compressor turn the gas back to liquid at a faster rate and therefore its cooling faster?? 

[Kevin Wood]

The Omega's air con compressor is variable displacement, I believe, so that compensates to some extent for engine speed and how much refrigerant is being let by by the expansion valve.

If the screen really is icing up, then so is the evaporator, and it will eventually block up, hence on a properly working system, the expansion valve keeps the evaporator above freezing. This also means the system only does as much work as it has to, meaning very little impact on fuel consumption.

[Mr Gav]

Clearly, if the system is under pressure a leak can be readily detected, but how can the same be said if the system is evacuated: there surely wouldn't ne any visible signs?

Ron.

You are actually very correct, it is a very flawed method of testing for leaks. Under vacuum the stresses the pressures on the system are the reverse of that which it sees when operating and only a fraction of what they would be under normal operating pressures (particularly on the high side).

To do it correctly you fill with a dry Nitrogen charge but, this clearly takes time and cash so is skipped at the risk of it leaking again.

What it will find is total failures of say the condenser, it wont identify weak seals or valves.

The trouble with testing under vacuum is that it pulls everything in tight so less chance of leaking, the cynic in me says that this is done on purpose as they are not allowed to fill a system they know is leaking and therefore thay don`t get any money for it.
I had the Datsun regassed last year which was ok under vacuum but within a week it wasn`t working again, last week I took it to a local garage and explained it had a leak so needed finding before any re gassing took place, they found a leak in each pipe from the compressor to the condenser and need replacing.

[Lazydocker]

I feel cheated if I pay more than £20... But that is a deal with my mate as he does all the MOTs on all the motors I look after.

Reminds me, I must book the A/C regards at the same time as the MOT

I know you can (in theory) change the rad without disconnecting the AC lines but much easier and, surprisingly, after over 4 years parked up there was still some gas

[Sir Tigger KC]

cheapest here  it's not rocket science


http://www.hotukdeals.com/deals/car-air-con-recharge-28-95-ats-euromaster-groupon-up-43-off-2721076

Just bought a/c recharge for both cars via this link and saved £38.08!  Thanks for sharing!