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is usually where I come in and at this point I start asking questions.
Many of the answers I would really like to know as they may require specialist
knowledge but there are some questions you could ask yourself and make
some judgements upon.
1. Bearing in mind the rule of thumb in the previous page, how long since
it was last charged? If you have owned the car for less than about two
years and have no other evidence then look further.
2. Is there enough air coming through the face-level-vents? Turn the blower
right up, put the air control to face-level and feel how much air is coming
out, insufficient could be the result of blocked pollen/dust filters if
you have them or a dislodged piece of air trunking under the dash or a
vent control that has stuck or even a blower motor not pulling it's weight.
Try pushing the recirculation button (your handbook will show you the
logo for this) - if more air comes out of the face-level vents then suspect
the pollen filters. If the blower motor is not going at all then the AC
will usually not work at all either.
3. The heater may be turned off but is it still working a little and spoiling
the AC? Turn off both heater and AC and with the car running on tickover
for say ten minutes, the bonnet closed and the blower operating, check
that the air from the vents is only at ambient temperature and is not
heated.
4. Is the AC compressor actually running at all? Look under the bonnet
at where the drive belt is running and get a friend to switch the AC on
and off a few times, not too quickly as some systems do not start for
several seconds after the switch has been pushed. You should hear a distinct
click as the clutch operates and you may then be able to identify which
is the compressor, you should then be able to observe that when the AC
is turned off the belt turns the pulley only but when it is switched on,
the outer plate (which is connected to the compressor internals) turns
also. If it does not turn, look first at the fuses - it could be something
really simple. Should an AC fuse have blown, before you replace it, check
that any electro fan on the radiator is able to turn freely - if it is
stiff it may draw excessive current and blow the fuse again. If no fuse
has blown probably the most likely scenario is that the gas pressure is
so low that the safety switch has operated to prevent the compressor turning
and risking damage. Double-check that the interior fan is actually running
- if this fails the AC will not run. Early systems using the large black
cylindrical Harrison or Frigidaire A6 compressor (mostly Jaguars and Rolls
in the UK) frequently used a strange three-legged fuse mounted on the
front end of the compressor, under adverse conditions this blows to protect
the compressor and to ensure that the system is looked at and preferably
recharged before the fuse is replaced - this is one fuse that almost certainly
means that a recharge is necessary, don't be tempted to just replace the
fuse without having the system checked out first.
If the
car is post 2000 and is a German car or a Skoda you may have a system
which uses one of the newer clutchless compressors. These appear to be
working all the time whether the AC is switched on or off and thus require
more equipment to diagnose. If you seem unable to turn it off but it still
underperforms then you need a specialist - its not really suitable for
self diagnosis.
5. Once you have ascertained that the compressor is running you could
try following the path of the thin pipe coming from the bottom of the
condenser (the front radiator). This will often go into a type of metal
bottle (the receiver/dryer) that will occasionally have a small glass
eye set into the top of it or possibly in a separate small block (this
is the sight-glass). Clean the glass and observe it whilst the compressor
is running. Is it virtually completely clear? If you can see a continuous
stream of bubbles or even what looks like foam then almost certainly the
system needs recharging. It is perfectly normal to see a few bubbles each
time the compressor starts and stops and if you have the later R134a refrigerant
a few bubbles may be seen continuously on a very cold day but otherwise
the sight-glass should show only a continuous flow of liquid. These sightglasses
are much less frequently encountered on more modern vehicles, only the
Japanese seem to still have faith in them.
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