Hi

I have a 1997 VW Polo that seems to have an air conditioning fault. Earlier
this year the air conditioning seemed to become less effective i.e. the air
was less cold than we were used to. I reported this at the car's recent
service at a VW dealer, and the dealer re-gassed the air conditioning
system, tested it and said it was ok. Apparently, their test is to put a
temperature sensor down the dashboard vent, turn the air conditioning on and
check that the temperature falls to 2°C.

Following the service, I am still doubtful that the air conditioning is
working properly, the air still does not seem to be very cold. I checked
the performance using a digital thermometer with the sensor in the dashboard
vent, on a warm day while driving the car and got the following results:

1) Switched off all vents except dashboard vent. Tested with the fan only.
Temp fluctuated between 9° and 10°C.

2) Switched on air conditioning - temp went down to 2°C briefly, then went
up to around 6°C. Stayed at 6°C.

3) Switched off air conditioning - temp went up to about 9°C

4) Switched on air conditioning again - went down to 2°C briefly and then up
again to around 6°C

5) Switched off air conditioning and eventually temp went up to 10°C

Please can anyone advise me whether there is a fault and how to fix it?

Thanks

David Aldrich

David

I have recently had a problem with my '96 polo's AC and so I have come
across quite a bit of reading over the last few days.

My problem was a noisy pulley wheel idler bearing on the AC's compressor.
Didn't affect the AC as it was only noisy when it was switched off! VW
wanted around £600 for a new compressor, I have changed the bearing for £30
and all is now quiet.

I read during my research that the AC should cool the inlet air down to
about 5 deg c so yours sounds about right. Have you checked that your pollen
filter isn't blocked? it has been a long dry dusty summer which causes these
filters to block in much less than a year. It sounds like you may not have
enough airflow so the compressor is switching off when it senses that it is
cooling too much. Try the temperature test with the recirculation on.


Vic


"David Aldrich" <aldrich (AT) NOJUNKeurobell (DOT) co.uk> wrote

Hi Vic

Thanks for your reply. I have checked the pollen filter and it looks
clean. Can you tell me:

a) What happens when the recirculation switch is switched on (how is the
internal air recirculated through the air conditioning unit) ?

b) How does the control system work that controls the compressor?

I will retry the temperature test with recirculation on, as you suggested.

Best regards

David

Dave

a) internal air is taken from an inlet high at the back of the passenger
footwell instead of through the pollen filter. the recirc switch causes a
flap to operate in the inlet piping

b) The AC ON switch operates a relay in the fuse box area (you should hear
it click) which provides a current to a large electromagnetic coil housed
in the compressor pulley wheel (the one on the alternator drivebelt) This
pulls the clutch plate at the end of the compressor onto the mating end of
the idler wheel and drives the compressor. There are also various protection
devices which can prevent this happening; If the gas pressure is too low
the relay is prevented from operating (this protects the compressor), and
also if the outside air temperature is below 5 deg C the AC does not
function also (It says this in the cars handbook) I don't know what the
reason for this is, probably to prevent icing.

Vic


"David Aldrich" <aldrich (AT) NOJUNKeurobell (DOT) co.uk> wrote

Hi Vic

Thanks for your reply. Today I tried the recirculation as you suggested. I
turned the fan speed to "1" and switched on the air con and recirculation. I
went for a drive and the temperature in the dash outlet stayed around 20C,
dipping to 17C when I turned the air con off then on. It then rose to 20C
again.

When I got home I fiddled with the fan control and air con switch and
suddenly the temperature plummeted to 0C and stayed there. I continued
fiddling and this time the temperature only fell to around 11C.

This is very odd. I think the gas must be fine but there must be some
control system fault. I wonder if you have any ideas? Perhaps I must
return to the VW dealer.

Best regards

David

"David Aldrich" <aldrich (AT) NOJUNKeurobell (DOT) co.uk> wrote

maybe a silly point but - air con is only fully efficient when a, set to
recirc and b, all windows and sunroof are closed.
you maybe already knew this did you ?

Sounds like it might be a problem with the fan control switch or a relay.
The AC will not be activated until the fan speed is set to '1' or higher.
Perhaps something is not sensing this or is intermittant.