In reply to a message from dtrain sent Wed 1 Aug 2012:
Checking blower operation is quite straightforward.
On your '92 model, turn the fan speed to ‘High’ and observe
the blower noise level. Pull fuse A2 in the right fuse box.
If it goes silent, the LH blower is not working (because you
have just switched off the RH blower which was working).
Conversely,if the noise level doesn’t change then the RH
blower is not working. You can confirm that after replacing
fuse A2, by pulling fuse B1 in the right fuse box. If it now
goes silent (having killed the LH blower) the RH is
confirmed as the one that is not working.
BTW, before ripping out the dash, since neither the centre
vents which require vacuum to open and the demist vents
which require vacuum to close appear to be working as they
should, are you sure you have manifold vacuum going to the
vacuum reservoir under the battery and if so, you need to
check the individual vacuum feeds from the solenoid valves
under the base of the climate control unit (CCU) and the
vacuum lines to those vents.
The centre vents have a black vacuum line and the demist
vents have a green vacuum line from their respective
solenoid valves both of which are on the right underside of
the CCU (demist nearest the firewall, centre vents furthest
from the firewall)
You can remove the vacuum line from its solenoid valve and
apply a vacuum to the line manually (Mityvac or similar) to
listen to the operation of the flaps as vacuum is applied or
The original message included these comments:
Thanks for copying that. I’m not sure how to check whether
both blowers are working. I did run through the tests and
it only works properly in defrost mode. Air comes out of
the demist vents all the time and never from the center
vents. So am I pulling this dash to fix this and if so, is
there a list of parts replace while I have it out so I
don’t have to do it again soon?
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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