[xj40] compresser clutch won`t engage

hi all. I cannot get my compresser clutch to engage . the
compresser turns and I can turn the front by hand .if I pull the
wires off the back of compresser there is no power from these
wires . I have changed the clutch relay with one I no works . and
i have changed the fuse in a5 on drivers side kick plate still no
power . am I missing somthing . I test with engine running . and
all controls set to cold with man control and air selected and
one or to drips lights showing on controls . and not in econ as I
know this turns a/c off any help is appreciated paul–
1990 sovereign 4lt s
northamptonshire, United Kingdom
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In reply to a message from cav sent Sat 17 Feb 2007:

Is the system charged with refrigerant? There’s a low pressure
cut-out switch screwed into the back head of the Sanden compressor
that opens at 35 psig to prevent damage to the compressor when the
charge is low.–
The original message included these comments:

hi all. I cannot get my compresser clutch to engage . the
compresser turns and I can turn the front by hand .if I pull the
wires off the back of compresser there is no power from these
wires . I have changed the clutch relay with one I no works . and
I have changed the fuse in a5 on drivers side kick plate still no
power . am I missing somthing . I test with engine running . and
all controls set to cold with man control and air selected and
one or to drips lights showing on controls . and not in econ as I
know this turns a/c off any help is appreciated paul


Pete 70 XKE (193K) 88 XJ6 (233K) 88 XJ6 (217K) 60 Mini
Severna Park, Maryland, United States
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Hi Paul,

There are several things that might prevent compressor clutch
engagement with the A/C panel controls properly set. One is lack of
ground to the compressor clutch relay due to low system pressure (loss
of refrigerant) or switch/wiring failure. According to the Compressor
Clutch circuit diagram in the JDHT CD, the low pressure switch
completes the ground to the clutch relay via the UB (Blue/Black) wire
to pin 85 of the relay.

So to bypass that switch, place a jumper from pin 85 to ground, with
the ignition on, engine off, and panel controls set to full A/C, and
see if both the relay and clutch click. If they do, you have found your
problem, and low refrigerant pressure rather than a failed switch is
the more likely problem. You can jumper pins 87 & 30 of the clutch
relay socket to “hotwire” the compressor clutch, bypassing both the
relay and low pressure switch.

Obviously you do NOT want to run the compressor if the system is low on
refrigerant, as oil will not circulate, and your compressor will be
damaged. If you have a manifold gauge set, I would suggest attaching
the gauges to the system to see what your system pressure at rest is.
If it is lower than ~ 25 PSIG, the switch will not close and you won’t
get compressor operation. If you have a can of refrigerant and a
charging handle, you should be able to add enough refrigerant (to the
low side) to get system pressure up enough to engage the clutch,
without the compressor running.

George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: pampaulcavaliers@aol.com

hi all. I cannot get my compresser clutch to engage . the
compresser turns and I can turn the front by hand .if I pull the
wires off the back of compresser there is no power from these
wires . I have changed the clutch relay with one I no works . and
i have changed the fuse in a5 on drivers side kick plate still no
power.


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In reply to a message from cav sent Sat 17 Feb 2007:

thanks for advise I will take car to be regassed .i am sure all
will be well after.–
1990 sovereign 4lt s
northamptonshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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