[xj] A/C amplifier questions

Jon Schrock wrote:

 The new amplifier kept the Green wire around 5.5V, but put the Blue

wire at 12V with no variation through the entire traverse of both the
temperature control knob and amplifier adjustment, again resulting in
constant cooling.

I’m also in the throes of trying to diagnose a wacky climate control.
You mention the blue wire to the amplifier. For what it’s worth, for
several days I monitored the voltage on the blue wire and found that the
equilibrium point (neither heating or cooling) is about 7.2 volts on
mine and full heating or cooling being no more than about 1 volt lower
or higher respectively. Never saw anything approaching 12 volts.

I understand that to be proper operation so now I’m monitoring the green
wire voltage waiting for the intermitent problem to rear its ugly head
again.

Good luck.

Tom

Hello everyone,

 This is a plea to Mike Morrin or anyone else out there who has

working knowledge of the '72-'87 Jaguar A/C amplifiers. Mike, thanks
for the excellent post of May 25 on this subject. It took me a step
further, but I’ve still got problems.

 My '85 XJ-S supplies only cold air.  To tackle the problem

initially I followed the flow chart in the Factory Service Manual. When
I checked the amplifier wiring, I found that it was supplying a constant
12V to the servo via the Red wire. When I measured resistance in the
Blue wire from the temperature control switch to the amplifier, I found
that it varied with movement of the control knob as it should. The only
other step suggested in the flow chart was measuring the resistances in
the circuit fo servo feedback (Green-Yellow and Yellow-Orange). Both of
these were appropriate at about 2000 ohms. According to the Manual this
indicated an amplifier problem.

 I purchased a new amplifier and installed it, only to find it did

the same thing - supplied only cold air. I figured I’d blown the
diagnosis, but when Mike posted his letter, I went back to recheck.
What I found was that, although the results were the same, the new and
old amplifiers were doing different things.

 Mike's note indicated that the Blue and Green wires should have

voltages of 5-6V, varying with temperature setting, with relative
voltages determining heating vs. cooling modes (Green > Blue = 12V on
Purple wire = heat; Blue > Green = 12V on Red wire = cold). The old
amplifier produced uniformly low voltages (2-4V) that varied with
temperature setting and amplifier adjustment, but never allowed the
voltage of the Green wire to exceed that of the Blue, resulting in
constant cooling.

 The new amplifier kept the Green wire around 5.5V, but put the Blue

wire at 12V with no variation through the entire traverse of both the
temperature control knob and amplifier adjustment, again resulting in
constant cooling.

 For those of you who've stuck with me this long: Am I missing

something wrong elsewhere in the system, or could my new amplifier be
faulty? Any suggestions would be greatly appreciated.

Thanks,
Jon Schrock
85 XJ-S
77 XJ12L
65 EType Cpe
56 XK140 FHC