[xj] A/C Compressor Wiring

“The Barkers” <@The_Barkers>

OK ya’ll did so well with the bumper height question, I thought I would get
a little more challenging with question number two. My A/C compressor does
not run although 12V is being send from the clutch fuse. Before taking is to
the A/C shop I thought I would verify that the problem is not electrical (it
seems to also be low on freon but without the compressor I’m not sure how
low). Here’s where it gets interesting. My wiring does not remotely resemble
that shown in the SIII manual. The manual shows the 12V signal and the
superheat switch (wire on back of compressor) going to a thermal fuse. One
lead from the fuse going to the clutch and the other clutch lead going to
ground. When the superheat switch closes and sources energy to ground the
fuse blows a few minutes later. Superheat switch stays open the 12V signal
activates the clutch and life is good.

Well, that makes sense but my wiring is --12V from clutch fuse directly to
the clutch. Wire from the back of compressor (superheat switch?) directly to
the other clutch lead. If I believe the manual, and basic electronic
principles, the wiring I have could have never worked. I have read of
thermal fuse retrofit involving a replacement of the fuse with a “GM Style”
low pressure switch. That is the only way I could justify my current wiring
dilemma but I can’t find the switch and the wire goes straight into the
compressor.

Any help solving the mystery would be most appreciated.

SteveB
Atlanta, GA, USA
87SIII===================================================
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“DOUGLAS DWYER” <@Doug_Dwyer>

Steve,
Hopefully another lister can validate or invalidate what I’m about to say as
I am not 100% certain…but…

I think Jag used two different configurations in production. A) Thermal
limiter with superheat switch OR B) low pressure switch without thermal
limiter. I’m pretty sure you have the type using only a low pressure switch.
These have the wiring directly to the clutch. If the pressure drops the
switch simply opens the circuit.

Interestingly, my '87 has the thermal limiter with superheat switch…

Doug Dwyer
Longview, Washington USA===================================================
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Gregory Wells <@Gregory_Wells3>

DOUGLAS DWYER wrote:

“DOUGLAS DWYER” DWYERD@email.msn.com

Steve,
Hopefully another lister can validate or invalidate what I’m about to say as
I am not 100% certain…but…

I think Jag used two different configurations in production. A) Thermal
limiter with superheat switch OR B) low pressure switch without thermal
limiter. I’m pretty sure you have the type using only a low pressure switch.
These have the wiring directly to the clutch. If the pressure drops the
switch simply opens the circuit.

Interestingly, my '87 has the thermal limiter with superheat switch…

Doug,

You are correct, as far as I know.

The thermal limit fuse was what was originally fitted and some time
later there was a Jaguar TSB which delineated the steps to eliminate the
thermal limit fuse, which evidently would blow during high load
conditions with everything at spec. There is an adapter lead to use when
installing the later compressor with the low pressure switch.

Best regards,

Gregory Wells
Coventry West, Inc.
New, Rebuilt, & Used Jaguar Parts


800-331-2193 x103===================================================
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