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. More recent cars present more problems for owners and
are less likely to be detectable without specialised equipment so the following
really applies to older models.
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? This is extremely
important. If you can feel some air but it seems weak, put the air control
to face-level, turn the blower speed to maximum and then feel how much
air is coming out. Insufficient is most likely to be the result of blocked
pollen/cabin filters as most modern cars have them or possibly 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. Cabin filters are usually replaced at
annual services - they last only about 9 to 12 months. 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 you cannot
feel any air, can you hear the blower motor turning? If necessary turn
the engine off, turn the ignition on again without starting the engine
and listen hard for the sound of the blower motor. Try all speeds in turn.
If the blower motor is not going at all then the AC will usually not work
at all either. Often if the blower refuses to work at one speed the AC
may be turned off as well.
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
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.
car is post 2000 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.
it be that cold air is coming out of one vent and hot air out of another.
We meet this occasionally and the distribution of the cooled air is sometimes
quite complex. Occasionally it is the result of a small plastic cog wheel
wearing out on the most commonly used teeth. Sometimes it is the result
of a stepper motor failing.
to the Contents Page
carry on to the next page