Omega Electronic Climate Control Problem

Hi, I have a 1998 3 litre Omega Elite fitted with the digital climate
control which has started to develop a very annoying problem now that winter
has arrived. On a cold day with the temperature set and the system heater on
no problem on a short journey. However on a longer journey with the cabin
pleasantly warm it suddenly seems to go into rapid cool down mode suddenly
blowing out cold air and if left on automatic the fan speed increases as if
on hot summer day mode. The only way then to get any warm air is to turn the
temperature right to the top on to the "Hi" setting which overrides the
auto settings and of course then becomes very hot. If the vehicle is stopped
for a while the system seems to start working again OK. This problem only
occurs on longer journeys when the heater has been running for some time and
I would suspect this may be a problem with whatever sensor controls the
interior cabin temperature. Its as if its suddenly erroneously telling the
air conditioning system its very hot, which of course then responds by
turning on the air conditioning, not very desirable when its only 3 degrees
outside.
I should be grateful for any advice from anyone with a bit of specialist
knowledge I fear this may be an expensive trip to the main dealer.

Many thanks - Mark

 

The sensor is behind the slotted hole on the climate control panel - they do
get full of dust so give it a blow out - not convinced this is the problem
though but worth trying.

 

my first thoughts also.

clean the sensor

then its time for a paperclip!

mike

 

First please reset ECC by pressing 'Auto' and 'Off' simultaneously for around 5 seconds.
AC compressor is not expected to work below some outside temperature, around +4 Centigrades if I remember.
JaC

 

Many thanks for all your suggestions. I have cleaned the sensor apature with
a vacum cleaner and done an "Auto and Off" reset. The system is presently
working but I suppose the next long journey will tell (normally about 1
hours driving produces the problem). Not entirely sure what you mean by its
time for a paper clip (poked in to unblock the apature intake ?). The other
thing I was wondering is there an air intake sampling fan to draw air in
from the cabin and could this have failed ?

Many thanks again
Mark

 

Paperclip refers to a diagnostic technique of shorting two pins on the
diagnostic connector to obtain a fault code. I've heard that this can be
done with the various computers (including climate control) but have
only actually experienced this with the engine / exhaust management
system. "Paperclip" is the cheap way to short the two pins, personally,
I could never be bothered to buy a paperclip, and always used a piece of
wire.

Back to your problem.

I'm sure that cleaning / etc. is the best place to start. However, from
your clear description of the problem where you suggest an intermittent
fault that results in the a/c failing to recognise the cabin
temperature, this suggests a failure of the signalling between the a/c
management and the sensor. Probable causes off top of my head (in order
of likelyhood) -

1) Dodgy connectors (try unplugging / cleaning / reseating any you can
find between a/c controller and the sensor)
2) Dry-joint or failed solder pad - either at the sensor (if mounted to
a PCB) - requires re-flowing or similar - hard to diagnose until you
find the problem
3) Failed sensor (internal fault) - should be noticable by manipulating
the sensor with the a/c running. If found, then replace with like from
scrappers.
4) Failed loom - real bugger to diagnose, easiest way to take the loom
out of the equation is to bi-wire the sensor to the controller -
duplicate the wire run for each sensor wire (e.g. if the sensor has two
wires in the cable loom going to it then run two parallel wires back to
the controller). This only needs to be a temporary hook up to understand
if the loom has failed. Once diagnosed, then you'd need to look at
making such a repair more permanent.