[xj] Climate Control doesn't know when to stop

XJ
1

Hi gang,

I could use some advice on a climate control problem. All thoughts
welcome…

Symptom: the system, fundamentally, is operational as intended…it cools,
it heats, the blowers self-adjust, etc. However, quite often (75% of the
time?) it just doesn’t know when to stop. For instance, if cooling is called
for the system will keep cooling long after the desired temperature is
reached. Similarly, when heat is called for, the system just keeps pumping
out heat until my toes roast. In either case only an adjustment of the temp
knob will reverse the action…and sometimes an exaggerated adjustment is
required. From time-to-time I get cold air when I expect warm air. But I
never get warm air when I expect cold.

The only pattern I can discern is this: when I jump into the car and drive
off, the system will stabilize and behaves fine UNTIL it decides the first
adjustment is called for. As soon as it self-adjusts ONCE, the undesired
behavior begins and will continue.

I did a couple of quick tests this morning. Both the ambient temp sensor and
in-car sensors are skewed, both “thinking” the cabin is colder than it
really is. This would perhaps explain why the system would want to pump out
heat for an extended period of time, but wouldn’t explain the
reverse—pumping out cold air long after the desired temperature has been
reached.

What I have not tested yet…silly me…is the resistance of the
temperature control itself. I will do that today. I have thought of
adjusting the potentiometer on the amplifier but have not done so, as it
seems to me that doing so would only address an issue where the system
over-cools or over-heats—but not both.

Thoughts so far?

I have swapped amplifiers, by the way, and it made no difference.

Doug Dwyer
Longview, Washington USA
1987 Ser III XJ6
1988 XJS V12===================================================
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2

Doug, sounds like something with the amplifier, since that looks at the
differences between set and sensed values, so could drive the system too hard
in either direction.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Doug Dwyer wrote:

Hi gang,

I could use some advice on a climate control problem. All thoughts
welcome…

Symptom: the system, fundamentally, is operational as intended…it cools,
it heats, the blowers self-adjust, etc. However, quite often (75% of the
time?) it just doesn’t know when to stop. For instance, if cooling is called
for the system will keep cooling long after the desired temperature is
reached. Similarly, when heat is called for, the system just keeps pumping
out heat until my toes roast. In either case only an adjustment of the temp
knob will reverse the action…and sometimes an exaggerated adjustment is
required. From time-to-time I get cold air when I expect warm air. But I
never get warm air when I expect cold.

The only pattern I can discern is this: when I jump into the car and drive
off, the system will stabilize and behaves fine UNTIL it decides the first
adjustment is called for. As soon as it self-adjusts ONCE, the undesired
behavior begins and will continue.

I did a couple of quick tests this morning. Both the ambient temp sensor and
in-car sensors are skewed, both “thinking” the cabin is colder than it
really is. This would perhaps explain why the system would want to pump out
heat for an extended period of time, but wouldn’t explain the
reverse—pumping out cold air long after the desired temperature has been
reached.

What I have not tested yet…silly me…is the resistance of the
temperature control itself. I will do that today. I have thought of
adjusting the potentiometer on the amplifier but have not done so, as it
seems to me that doing so would only address an issue where the system
over-cools or over-heats—but not both.

Thoughts so far?

I have swapped amplifiers, by the way, and it made no difference.

===================================================
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3

My thoughts exactly ! However, I guess you missed the part of my posting
which said “I have swapped amplifiers, by the way, and it made no
difference.”

Thanks anyhow, Alex :slight_smile:

Doug Dwyer
Longview, Washington USA
1987 Ser III XJ6
1988 XJS V12

Doug, sounds like something with the amplifier, since that looks at the
differences between set and sensed values, so could drive the system too
hardFrom: “Cannara” cannara@attglobal.net
in either direction.

===================================================
The archives and FAQ will answer many queries on the XJ series…
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4

Doug Dwyer wrote:

Hi gang,

I could use some advice on a climate control problem. All thoughts
welcome…

Symptom: the system, fundamentally, is operational as intended…it cools,
it heats, the blowers self-adjust, etc. However, quite often (75% of the
time?) it just doesn’t know when to stop. For instance, if cooling is called
for the system will keep cooling long after the desired temperature is
reached. Similarly, when heat is called for, the system just keeps pumping
out heat until my toes roast. In either case only an adjustment of the temp
knob will reverse the action…and sometimes an exaggerated adjustment is
required. From time-to-time I get cold air when I expect warm air. But I
never get warm air when I expect cold.

The only pattern I can discern is this: when I jump into the car and drive
off, the system will stabilize and behaves fine UNTIL it decides the first
adjustment is called for. As soon as it self-adjusts ONCE, the undesired
behavior begins and will continue.

I did a couple of quick tests this morning. Both the ambient temp sensor and
in-car sensors are skewed, both “thinking” the cabin is colder than it
really is. This would perhaps explain why the system would want to pump out
heat for an extended period of time, but wouldn’t explain the
reverse—pumping out cold air long after the desired temperature has been
reached.

What I have not tested yet…silly me…is the resistance of the
temperature control itself. I will do that today. I have thought of
adjusting the potentiometer on the amplifier but have not done so, as it
seems to me that doing so would only address an issue where the system
over-cools or over-heats—but not both.

Thoughts so far?

I have swapped amplifiers, by the way, and it made no difference.

Only tested components are working components, Doug - which is rather
selfcontradictory in this case as replacement is the only realistic test
option, but…:slight_smile:

A thought experiment; the system is cooling down the car properly, but
sensing that the car is now too cold it correctly turns to full heat.
However; the heater valve remains closed and delivers cold air. The amp
has no way of actually knowing this; it procedes to “heat” at full speed
delivering only more cold air…

In principle; as far as I know, the heater valve controls are the same
as the ones used to activate defrost. But I don’t really KNOW it for a
fact, nor do I positively know if the water valve is either fully open,
fully closed or have a varable setting - but it may be sticky…? So if
the system correctly delivers hot air set to def it may or may not
signal a working water valve/heater core, but…

If cold air is coming out of the fascia side vents adjacent to the
center vent, and the center vent is closed the system is certainly in
full heating mode. Which is the correct one for a too cold car. (If too
hot only the center flap is open, of course…). If the flap settings
are “confused” it is likely an amplifier fault, or, somewhat more
unlikely; the servo is failing in some way. The side window vents is
manually controlled, but usually delivers warm air - if there is any…?

It is, of course also possible that only specific flaps (controls) have
failed, but that should have more “discrete” consequenses? And you are
also probably quite right in suspecting some sensor fault - to be
investigated as you imply. In general, though; erratic or inconsistent
reactions are usually attributed to the amplifier, the servo being
usually reliable - though not infallible…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
The archives and FAQ will answer many queries on the XJ series…
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5

A thought experiment;

That’s what we love about you, Frank :slight_smile:

nor do I positively know if the water valve is either fully open,
fully closed or have a varable setting - but it may be sticky…? So if
the system correctly delivers hot air set to def it may or may not
signal a working water valve/heater core, but…

Hmmm. Foolish of me not to consider the heater valve first. It is worth a
look. It is easy to fall into a trap of anticipating a difficult solution
before checking the easy stuff. I need to follow my own advice, eh ? A
heater valve problem would be easy enough to fix. If that’s the case,
though, and it cures my problem, I am left in an even bigger quandry about
my skewed sensor readings. Nothing that I couldn’t shrug off in, oh, 12
seconds or so, though :slight_smile:

If the flap settings
are “confused” it is likely an amplifier fault, or, somewhat more
unlikely; the servo is failing in some way. The side window vents is
manually controlled, but usually delivers warm air - if there is any…?

Yes, warm air at the side window vents. In fact, in terms of air flow and
distribution, everything seems correct, which tells me the system is trying
to do the right thing. It is just temperature regulation that fails…

It is, of course also possible that only specific flaps (controls) have
failed, but that should have more “discrete” consequenses?

Oh, geez. There’s only about a hundred widgets in the system. I am praying
for something terribly “indescrete”. I am not really interested in becoming
an expert on the system. An easy fix, and continuance of my amatuer
standing, is perfectly OK with
me :slight_smile:

Thanks for the thought starters, Frank

Cheers
Doug DwyerFrom: “Frank Andersen” franksue@xtra.co.nz

===================================================
The archives and FAQ will answer many queries on the XJ series…
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6

In reply to a message from Doug Dwyer sent Sun 31 Oct 2004:

Doug, the water valve could be a possibility if it’s sticking and
how about these options:

ROM pg 82-35; In Car Temp Sensor
ROM pg 82-36; Thermostat (fig 73)
ROM pg 82-36; Water Valve Temp Sw (fig 71)

Or perhaps any/all of the electrical connectors to them?–
The original message included these comments:

Oh, geez. There’s only about a hundred widgets in the system. I am praying
for something terribly ‘‘indescrete’’. I am not really interested in becoming
an expert on the system. An easy fix, and continuance of my amatuer
standing, is perfectly OK with
me :slight_smile:
Thanks for the thought starters, Frank
Cheers
Doug Dwyer

–
Jamie - 88 SIII V12 VdP & 89 XJS Conv
Tulalip, WA, United States
–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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7

Thanks, Jamie. We’re both thinking along the same lines. I have not checked
the ranco thermostat but did get some odd readings at both the in-car and
ambient sensors.

However, I have suspended testing for a couple of days as I may have fixed
the problem already…just want to verify that it is fixed before I
post the embarrassingly simple fault that I overlooked :slight_smile:

No point in looking like a fool unnecessarily, right ? :slight_smile:

Doug Dwyer
Longview, Washington USA
1987 Ser III XJ6
1988 XJS V12From: “NWJag” nwjag@jlduffey.org

In reply to a message from Doug Dwyer sent Sun 31 Oct 2004:

Doug, the water valve could be a possibility if it’s sticking and
how about these options:

ROM pg 82-35; In Car Temp Sensor
ROM pg 82-36; Thermostat (fig 73)
ROM pg 82-36; Water Valve Temp Sw (fig 71)

===================================================
The archives and FAQ will answer many queries on the XJ series…
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