In reply to a message from Cravo sent Sun 3 Feb 2008:
Tom,
This subject has been covered extensively on the forum in
the past. Here is an extract from the XJ40 archives of a
simple test you can do to determine if the system is
functioning correctly:-
The system relies on electrically operated
blend flaps in the climate control unit (CCU) to adjust the
temperature of the air exiting the vents and vacuum operated
duct flaps to direct the air through the chosen vents.
Sometimes a CCU blend flap gets stuck through lack of use
and the system cannot control the temperature exiting the vents.
You may be able to determine where the problem lies by
conducting this simple initial test :-
With the engine up to normal operating temperature, set the
temperature control knob on the panel to ‘Full Cool’ in
‘Manual’ mode with the fan speed on ‘Defrost’ (nothing else
selected)
You should get:-
- Hot air at full volume out of the DEMIST vents
- Some air out of the SIDE face vents
- NO air out of the CENTRE face vents
- NO air out of the FOOT WELL vents
Turn the fan speed control to ‘High’.
After a delay of, perhaps, 45 seconds, you should get:-
5) NO air out of the DEMIST vents
6) Cold air out of the SIDE face vents
7) Cold air out of the CENTRE face vents
8) Cold air out of the FOOT WELL vents
Turn the temperature control knob to ‘Full Heat’
After a delay of, perhaps, 45 seconds, you should get:-
9) NO air out of the DEMIST vents
10) Hot air out of the SIDE face vents
11) NO air out of the CENTRE face vents
12) Hot air out of the FOOT WELL vents.
NOTES:
- The ‘45 seconds’ delay is to allow the ECU / system to
react to the new selection - and to avoid ‘hunting’.
- You can REDUCE the temperature exiting the face level
vents in relation to that exiting the footwell vents by
moving the slider control from ‘hot’ (temperatures the same)
to cold (face level cooler)
- You can introduce demisting by selecting the ‘AIR’ (or
‘Screen’) button on the panel
- You can alter the dehumidifying effect of the A/C by using
the ‘raindrops’ buttons or cut out the A/C compressor
completely by selecting ‘ECON’
- In ‘Auto’ mode (not ‘Manual’) the ECU varies the fan speed
on ‘Low’ and ‘Medium’ only but not on ‘High’ or ‘Defrost’.
Post the results of 1 to 12.
From your description, it sounds as if the blend flaps in
the CCU are stuck in the ‘full heat’ position. ALL of the
air entering the CCU is at ambient temperature (refrigerated
if the A/C is working) by passing through the A/C
evaporator. If the blend flaps are in the ‘full cool’
position, that refrigerated air will by-pass the heater
matrix and exit the CCU as cold air out of the cabin vents.
Normally you need to select ‘heat’ for those blend flaps to
move in to a position to divert the cold air through the
heater matrix to warm it up - but if one or both flaps is
stuck in the ‘full heat’ position, ALL the air will be
diverted / heated, despite having the A/C selected.–
The original message included these comments:
Thanks, for the help. The car is an 88 model, I ran the test
and the clutch is engaging the air just doesnt seem to be
cold at all.
–
Bryan N, '91 Sovereign 4.0 L, RHD (exiled in US)
Cambridgeshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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