From: Duncan Wood on 7 Jul 2010 16:44
On Wed, 07 Jul 2010 21:33:05 +0100, Mike G
> "Mrcheerful" <nbkm57(a)hotmail.co.uk> wrote in message
>> Mike G wrote:
>>> "Mrcheerful" <nbkm57(a)hotmail.co.uk> wrote in message
>>>> mind you one of my customers went to kwik fit for an aircon recharge,
>>>> after about an hour they said they did not know why it would not
>>>> work. I look forward to seeing the car in a month or so for its
>>>> mot, I'll check out the aircon then and see what is really up.
>>> In your earlier post you said there will be some moisture in the
>>> system. I can understand how that can occur if all the gas escapes,
>>> but if the A/C system is still working, allbeit at reduced
>>> efficiency, how does moisture enter a system that must still contains
>>> pressure? Appears illogical. Mike
>> not actually, when the air con runs with a reduced charge it can go into
>> negative pressure on the suction side of the pump, it then draws in
>> air/moisture anywhere it can, through joints and even through the rubber
>> hose itself.
> I can understand how negative pressure could allow moisture to be drawn
> but would the system still work if that were the case?.
> If one accepts that the performance of auto A/C systems usually
> over years because of gradual gas loss, it would seem logical that if one
> adds gas before negative pressure allows moisture into the system, that a
> full purge of the system and refill can be avoided without detriment to
For maximum effeciency the evaporator nearly always works under less than
1 atm of pressure, adding more fluid (short of massively overfilling it)
won't stop that.